Update upstream source from tag 'upstream/1.0.28'

Update to upstream version '1.0.28'
with Debian dir ec5bb298266630fc3801ff6dc0c258f6df7ba979

1 files changed, 4415 insertions, 0 deletions

diff --git a/backend/genesys_gl843.cc b/backend/genesys_gl843.cc
new file mode 100644
index 0000000..a72dc5a
--- /dev/null
+++ b/backend/genesys_gl843.cc
@@ -0,0 +1,4415 @@
+/* sane - Scanner Access Now Easy.
+
+   Copyright (C) 2010-2013 Stéphane Voltz <stef.dev@free.fr>
+
+
+   This file is part of the SANE package.
+
+   This program is free software; you can redistribute it and/or
+   modify it under the terms of the GNU General Public License as
+   published by the Free Software Foundation; either version 2 of the
+   License, or (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 59 Temple Place - Suite 330, Boston,
+   MA 02111-1307, USA.
+
+   As a special exception, the authors of SANE give permission for
+   additional uses of the libraries contained in this release of SANE.
+
+   The exception is that, if you link a SANE library with other files
+   to produce an executable, this does not by itself cause the
+   resulting executable to be covered by the GNU General Public
+   License.  Your use of that executable is in no way restricted on
+   account of linking the SANE library code into it.
+
+   This exception does not, however, invalidate any other reasons why
+   the executable file might be covered by the GNU General Public
+   License.
+
+   If you submit changes to SANE to the maintainers to be included in
+   a subsequent release, you agree by submitting the changes that
+   those changes may be distributed with this exception intact.
+
+   If you write modifications of your own for SANE, it is your choice
+   whether to permit this exception to apply to your modifications.
+   If you do not wish that, delete this exception notice.
+*/
+
+#define DEBUG_DECLARE_ONLY
+
+#include "genesys_gl843.h"
+
+#include <string>
+#include <vector>
+
+/****************************************************************************
+ Low level function
+ ****************************************************************************/
+
+/* ------------------------------------------------------------------------ */
+/*                  Read and write RAM, registers and AFE                   */
+/* ------------------------------------------------------------------------ */
+
+/* Set address for writing data */
+static SANE_Status
+gl843_set_buffer_address (Genesys_Device * dev, uint32_t addr)
+{
+  SANE_Status status = SANE_STATUS_GOOD;
+
+  DBG(DBG_io, "%s: setting address to 0x%05x\n", __func__, addr & 0xffff);
+
+  status = sanei_genesys_write_register (dev, 0x5b, ((addr >> 8) & 0xff));
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed while writing high byte: %s\n", __func__, sane_strstatus(status));
+      return status;
+    }
+
+  status = sanei_genesys_write_register (dev, 0x5c, (addr & 0xff));
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed while writing low byte: %s\n", __func__, sane_strstatus(status));
+      return status;
+    }
+
+  DBG(DBG_io, "%s: completed\n", __func__);
+
+  return status;
+}
+
+/**
+ * writes a block of data to RAM
+ * @param dev USB device
+ * @param addr RAM address to write to
+ * @param size size of the chunk of data
+ * @param data pointer to the data to write
+ */
+static SANE_Status
+write_data (Genesys_Device * dev, uint32_t addr, uint32_t size,
+	    uint8_t * data)
+{
+  SANE_Status status = SANE_STATUS_GOOD;
+
+  DBGSTART;
+
+  status = gl843_set_buffer_address (dev, addr);
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed while setting address for bulk write data: %s\n", __func__,
+          sane_strstatus(status));
+      return status;
+    }
+
+  /* write actual data */
+  status = sanei_genesys_bulk_write_data(dev, 0x28, data, size);
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed while writing bulk write data: %s\n", __func__,
+          sane_strstatus(status));
+      return status;
+    }
+
+  /* set back address to 0 */
+  status = gl843_set_buffer_address (dev, 0);
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed setting to default RAM address: %s\n", __func__,
+          sane_strstatus(status));
+      return status;
+    }
+  DBGCOMPLETED;
+  return status;
+}
+
+/****************************************************************************
+ Mid level functions
+ ****************************************************************************/
+
+static SANE_Bool
+gl843_get_fast_feed_bit (Genesys_Register_Set * regs)
+{
+  GenesysRegister *r = NULL;
+
+  r = sanei_genesys_get_address (regs, REG02);
+  if (r && (r->value & REG02_FASTFED))
+    return SANE_TRUE;
+  return SANE_FALSE;
+}
+
+static SANE_Bool
+gl843_get_filter_bit (Genesys_Register_Set * regs)
+{
+  GenesysRegister *r = NULL;
+
+  r = sanei_genesys_get_address (regs, REG04);
+  if (r && (r->value & REG04_FILTER))
+    return SANE_TRUE;
+  return SANE_FALSE;
+}
+
+static SANE_Bool
+gl843_get_lineart_bit (Genesys_Register_Set * regs)
+{
+  GenesysRegister *r = NULL;
+
+  r = sanei_genesys_get_address (regs, REG04);
+  if (r && (r->value & REG04_LINEART))
+    return SANE_TRUE;
+  return SANE_FALSE;
+}
+
+static SANE_Bool
+gl843_get_bitset_bit (Genesys_Register_Set * regs)
+{
+  GenesysRegister *r = NULL;
+
+  r = sanei_genesys_get_address (regs, REG04);
+  if (r && (r->value & REG04_BITSET))
+    return SANE_TRUE;
+  return SANE_FALSE;
+}
+
+static SANE_Bool
+gl843_get_gain4_bit (Genesys_Register_Set * regs)
+{
+  GenesysRegister *r = NULL;
+
+  r = sanei_genesys_get_address (regs, REG06);
+  if (r && (r->value & REG06_GAIN4))
+    return SANE_TRUE;
+  return SANE_FALSE;
+}
+
+/**
+ * compute the step multiplier used
+ */
+static int
+gl843_get_step_multiplier (Genesys_Register_Set * regs)
+{
+  GenesysRegister *r = NULL;
+  int value = 1;
+
+  r = sanei_genesys_get_address (regs, REG9D);
+  if (r != NULL)
+    {
+      switch (r->value & 0x0c)
+	{
+	case 0x04:
+	  value = 2;
+	  break;
+	case 0x08:
+	  value = 4;
+	  break;
+	default:
+	  value = 1;
+	}
+    }
+  DBG(DBG_io, "%s: step multiplier is %d\n", __func__, value);
+  return value;
+}
+
+static SANE_Bool
+gl843_test_buffer_empty_bit (SANE_Byte val)
+{
+  if (val & REG41_BUFEMPTY)
+    return SANE_TRUE;
+  return SANE_FALSE;
+}
+
+static SANE_Bool
+gl843_test_motor_flag_bit (SANE_Byte val)
+{
+  if (val & REG41_MOTORENB)
+    return SANE_TRUE;
+  return SANE_FALSE;
+}
+
+/** copy sensor specific settings */
+static void
+gl843_setup_sensor (Genesys_Device * dev, const Genesys_Sensor& sensor,
+                    Genesys_Register_Set * regs, int dpi,int flags)
+{
+    (void) dpi;
+    (void) flags;
+
+    DBGSTART;
+
+    for (const auto& custom_reg : sensor.custom_regs) {
+        regs->set8(custom_reg.address, custom_reg.value);
+    }
+    if (!(dev->model->flags & GENESYS_FLAG_FULL_HWDPI_MODE)) {
+        regs->set8(0x7d, 0x90);
+    }
+
+    DBGCOMPLETED;
+}
+
+
+/** @brief set all registers to default values .
+ * This function is called only once at the beginning and
+ * fills register startup values for registers reused across scans.
+ * Those that are rarely modified or not modified are written
+ * individually.
+ * @param dev device structure holding register set to initialize
+ */
+static void
+gl843_init_registers (Genesys_Device * dev)
+{
+  // Within this function SENSOR_DEF marker documents that a register is part
+  // of the sensors definition and the actual value is set in
+  // gl843_setup_sensor().
+
+  DBGSTART;
+
+  dev->reg.clear();
+
+  /* default to KV-SS080 */
+  SETREG (0xa2, 0x0f);
+  if (dev->model->model_id == MODEL_CANON_CANOSCAN_8600F)
+    {
+      SETREG(0xa2, 0x1f);
+    }
+  SETREG (0x01, 0x00);
+  SETREG (0x02, 0x78);
+  SETREG (0x03, 0x1f);
+  SETREG (0x04, 0x10);
+
+  // fine tune upon device description
+  SETREG (0x05, 0x80);
+  if (dev->model->model_id == MODEL_HP_SCANJET_G4010 ||
+      dev->model->model_id == MODEL_HP_SCANJET_G4050 ||
+      dev->model->model_id == MODEL_HP_SCANJET_4850C)
+    {
+      SETREG (0x05, 0x08);
+    }
+
+  dev->reg.find_reg(0x05).value &= ~REG05_DPIHW;
+  switch (sanei_genesys_find_sensor_any(dev).optical_res)
+    {
+    case 600:
+      dev->reg.find_reg(0x05).value |= REG05_DPIHW_600;
+      break;
+    case 1200:
+      dev->reg.find_reg(0x05).value |= REG05_DPIHW_1200;
+      break;
+    case 2400:
+      dev->reg.find_reg(0x05).value |= REG05_DPIHW_2400;
+      break;
+    case 4800:
+      dev->reg.find_reg(0x05).value |= REG05_DPIHW_4800;
+      break;
+    }
+
+  // TODO: on 8600F the windows driver turns off GAIN4 which is recommended
+  SETREG (0x06, 0xd8); /* SCANMOD=110, PWRBIT and GAIN4 */
+  SETREG (0x08, 0x00);
+  SETREG (0x09, 0x00);
+  SETREG (0x0a, 0x00);
+
+  // This register controls clock and RAM settings and is further modified in
+  // gl843_boot
+  SETREG (0x0b, 0x6a);
+
+  if (dev->model->model_id == MODEL_CANON_CANOSCAN_8600F)
+    {
+      SETREG(0x0b, 0x89);
+    }
+
+  // EXPR[0:15], EXPG[0:15], EXPB[0:15]: Exposure time settings.
+  SETREG(0x10, 0x00); // SENSOR_DEF
+  SETREG(0x11, 0x00); // SENSOR_DEF
+  SETREG(0x12, 0x00); // SENSOR_DEF
+  SETREG(0x13, 0x00); // SENSOR_DEF
+  SETREG(0x14, 0x00); // SENSOR_DEF
+  SETREG(0x15, 0x00); // SENSOR_DEF
+  if (dev->model->model_id == MODEL_CANON_CANOSCAN_8600F)
+    {
+      dev->reg.set16(REG_EXPR, 0x9c40);
+      dev->reg.set16(REG_EXPG, 0x9c40);
+      dev->reg.set16(REG_EXPB, 0x9c40);
+    }
+  // CCD signal settings.
+  SETREG(0x16, 0x33); // SENSOR_DEF
+  SETREG(0x17, 0x1c); // SENSOR_DEF
+  SETREG(0x18, 0x10); // SENSOR_DEF
+
+  // EXPDMY[0:7]: Exposure time of dummy lines.
+  SETREG(0x19, 0x2a); // SENSOR_DEF
+
+  // Various CCD clock settings.
+  SETREG(0x1a, 0x04); // SENSOR_DEF
+  SETREG(0x1b, 0x00); // SENSOR_DEF
+  SETREG(0x1c, 0x20); // SENSOR_DEF
+  SETREG(0x1d, 0x04); // SENSOR_DEF
+
+  SETREG (0x1e, 0x10);
+  if (dev->model->model_id == MODEL_CANON_CANOSCAN_8600F)
+    {
+      SETREG(0x1e, 0x20);
+    }
+
+  SETREG (0x1f, 0x01);
+  if (dev->model->model_id == MODEL_CANON_CANOSCAN_8600F)
+    {
+      SETREG(0x1f, 0xff);
+    }
+
+  SETREG (0x20, 0x10);
+  SETREG (0x21, 0x04);
+  SETREG (0x22, 0x01);
+  if (dev->model->model_id == MODEL_CANON_CANOSCAN_8600F)
+    {
+      SETREG(0x22, 0xc8);
+    }
+
+  SETREG (0x23, 0x01);
+  if (dev->model->model_id == MODEL_CANON_CANOSCAN_8600F)
+    {
+      SETREG(0x23, 0xc8);
+    }
+
+  SETREG (0x24, 0x04);
+  SETREG (0x25, 0x00);
+  SETREG (0x26, 0x00);
+  SETREG (0x27, 0x00);
+  SETREG (0x2c, 0x02);
+  SETREG (0x2d, 0x58);
+  // BWHI[0:7]: high level of black and white threshold
+  SETREG (0x2e, 0x80);
+  // BWLOW[0:7]: low level of black and white threshold
+  SETREG (0x2f, 0x80);
+  SETREG (0x30, 0x00);
+  SETREG (0x31, 0x14);
+  SETREG (0x32, 0x27);
+  SETREG (0x33, 0xec);
+
+  // DUMMY: CCD dummy and optically black pixel count
+  SETREG (0x34, 0x24);
+  if (dev->model->model_id == MODEL_CANON_CANOSCAN_8600F)
+    {
+      SETREG(0x34, 0x14);
+    }
+
+  // MAXWD: If available buffer size is less than 2*MAXWD words, then
+  // "buffer full" state will be set.
+  SETREG (0x35, 0x00);
+  SETREG (0x36, 0xff);
+  SETREG (0x37, 0xff);
+
+  // LPERIOD: Line period or exposure time for CCD or CIS.
+  SETREG(0x38, 0x55); // SENSOR_DEF
+  SETREG(0x39, 0xf0); // SENSOR_DEF
+
+  // FEEDL[0:24]: The number of steps of motor movement.
+  SETREG(0x3d, 0x00);
+  SETREG (0x3e, 0x00);
+  SETREG (0x3f, 0x01);
+
+  // Latch points for high and low bytes of R, G and B channels of AFE. If
+  // multiple clocks per pixel are consumed, then the setting defines during
+  // which clock the corresponding value will be read.
+  // RHI[0:4]: The latch point for high byte of R channel.
+  // RLOW[0:4]: The latch point for low byte of R channel.
+  // GHI[0:4]: The latch point for high byte of G channel.
+  // GLOW[0:4]: The latch point for low byte of G channel.
+  // BHI[0:4]: The latch point for high byte of B channel.
+  // BLOW[0:4]: The latch point for low byte of B channel.
+  SETREG(0x52, 0x01); // SENSOR_DEF
+  SETREG(0x53, 0x04); // SENSOR_DEF
+  SETREG(0x54, 0x07); // SENSOR_DEF
+  SETREG(0x55, 0x0a); // SENSOR_DEF
+  SETREG(0x56, 0x0d); // SENSOR_DEF
+  SETREG(0x57, 0x10); // SENSOR_DEF
+
+  // VSMP[0:4]: The position of the image sampling pulse for AFE in cycles.
+  // VSMPW[0:2]: The length of the image sampling pulse for AFE in cycles.
+  SETREG(0x58, 0x1b); // SENSOR_DEF
+
+  SETREG(0x59, 0x00); // SENSOR_DEF
+  SETREG(0x5a, 0x40); // SENSOR_DEF
+
+  // 0x5b-0x5c: GMMADDR[0:15] address for gamma or motor tables download
+  // SENSOR_DEF
+
+  // DECSEL[0:2]: The number of deceleratino steps after touching home sensor
+  // STOPTIM[0:4]: The stop duration between change of directions in
+  // backtracking
+  SETREG (0x5e, 0x23);
+  if (dev->model->model_id == MODEL_CANON_CANOSCAN_8600F)
+    {
+      SETREG(0x5e, 0x1f);
+    }
+
+  // FMOVDEC: The number of deceleration steps in table 5 for auto-go-home
+  SETREG (0x5f, 0x01);
+  if (dev->model->model_id == MODEL_CANON_CANOSCAN_8600F)
+    {
+      SETREG(0x5f, 0xf0);
+    }
+
+  // Z1MOD[0:20]
+  SETREG (0x60, 0x00);
+  SETREG (0x61, 0x00);
+  SETREG (0x62, 0x00);
+
+  // Z2MOD[0:20]
+  SETREG (0x63, 0x00);
+  SETREG (0x64, 0x00);
+  SETREG (0x65, 0x00);
+
+  // STEPSEL[0:1]. Motor movement step mode selection for tables 1-3 in
+  // scanning mode.
+  // MTRPWM[0:5]. Motor phase PWM duty cycle setting for tables 1-3
+  SETREG (0x67, 0x7f);
+  // FSTPSEL[0:1]: Motor movement step mode selection for tables 4-5 in
+  // command mode.
+  // FASTPWM[5:0]: Motor phase PWM duty cycle setting for tables 4-5
+  SETREG (0x68, 0x7f);
+
+  // FSHDEC[0:7]: The number of deceleration steps after scanning is finished
+  // (table 3)
+  SETREG (0x69, 0x01);
+  if (dev->model->model_id == MODEL_CANON_CANOSCAN_8600F)
+    {
+      SETREG(0x69, 64);
+    }
+
+  // FMOVNO[0:7] The number of acceleration or deceleration steps for fast
+  // moving (table 4)
+  SETREG (0x6a, 0x04);
+  if (dev->model->model_id == MODEL_CANON_CANOSCAN_8600F)
+    {
+      SETREG(0x69, 64);
+    }
+
+  // GPIO-related register bits
+  SETREG (0x6b, 0x30);
+  if (dev->model->model_id == MODEL_CANON_CANOSCAN_8600F)
+    {
+      SETREG(0x6b, 0x72);
+    }
+
+  // 0x6c, 0x6d, 0x6e, 0x6f are set according to gpio tables. See
+  // gl843_init_gpio.
+
+  // RSH[0:4]: The position of rising edge of CCD RS signal in cycles
+  // RSL[0:4]: The position of falling edge of CCD RS signal in cycles
+  // CPH[0:4]: The position of rising edge of CCD CP signal in cycles.
+  // CPL[0:4]: The position of falling edge of CCD CP signal in cycles
+  SETREG(0x70, 0x01); // SENSOR_DEF
+  SETREG(0x71, 0x03); // SENSOR_DEF
+  SETREG (0x72, 0x04);
+  SETREG (0x73, 0x05);
+
+  if (dev->model->model_id == MODEL_CANON_CANOSCAN_8600F)
+    {
+      SETREG(0x70, 0x00);
+      SETREG(0x71, 0x02);
+      SETREG(0x72, 0x02);
+      SETREG(0x73, 0x04);
+    }
+
+  // CK1MAP[0:17], CK3MAP[0:17], CK4MAP[0:17]: CCD clock bit mapping setting.
+  SETREG(0x74, 0x00); // SENSOR_DEF
+  SETREG(0x75, 0x00); // SENSOR_DEF
+  SETREG(0x76, 0x3c); // SENSOR_DEF
+  SETREG(0x77, 0x00); // SENSOR_DEF
+  SETREG(0x78, 0x00); // SENSOR_DEF
+  SETREG(0x79, 0x9f); // SENSOR_DEF
+  SETREG(0x7a, 0x00); // SENSOR_DEF
+  SETREG(0x7b, 0x00); // SENSOR_DEF
+  SETREG(0x7c, 0x55); // SENSOR_DEF
+
+  // various AFE settings
+  SETREG(0x7d, 0x00);
+
+  // GPOLED[x]: LED vs GPIO settings
+  SETREG(0x7e, 0x00);
+
+  // BSMPDLY, VSMPDLY
+  // LEDCNT[0:1]: Controls led blinking and its period
+  SETREG (0x7f, 0x00);
+
+  // VRHOME, VRMOVE, VRBACK, VRSCAN: Vref settings of the motor driver IC for
+  // moving in various situations.
+  SETREG (0x80, 0x00);
+
+  if (dev->model->model_id != MODEL_CANON_CANOSCAN_4400F)
+    {
+      // NOTE: Historical code. None of the following 6 registers are
+      // documented in the datasheet. Their default value is 0, so probably it's
+      // not a bad idea to leave this here.
+      SETREG (0x81, 0x00);
+      SETREG (0x82, 0x00);
+      SETREG (0x83, 0x00);
+      SETREG (0x84, 0x00);
+      SETREG (0x85, 0x00);
+      SETREG (0x86, 0x00);
+    }
+
+  SETREG (0x87, 0x00);
+  if (dev->model->model_id == MODEL_CANON_CANOSCAN_8600F)
+    {
+      SETREG(0x87, 0x02);
+    }
+
+  // MTRPLS[0:7]: The width of the ADF motor trigger signal pulse.
+  if (dev->model->model_id == MODEL_CANON_CANOSCAN_8600F)
+    {
+      SETREG(0x94, 0xff);
+    }
+
+  // 0x95-0x97: SCANLEN[0:19]: Controls when paper jam bit is set in sheetfed
+  // scanners.
+
+  // ONDUR[0:15]: The duration of PWM ON phase for LAMP control
+  // OFFDUR[0:15]: The duration of PWM OFF phase for LAMP control
+  // both of the above are in system clocks
+  if (dev->model->model_id == MODEL_CANON_CANOSCAN_8600F)
+    {
+      SETREG(0x98, 0x00);
+      SETREG(0x99, 0x00);
+      SETREG(0x9a, 0x00);
+      SETREG(0x9b, 0x00);
+    }
+
+  // RMADLY[0:1], MOTLAG, CMODE, STEPTIM, MULDMYLN, IFRS
+  SETREG(0x9d, 0x04);
+  if (dev->model->model_id == MODEL_CANON_CANOSCAN_8600F)
+    {
+      SETREG(0x9d, 0x08); // additionally sets the multiplier for slope tables
+    }
+
+
+  // SEL3INV, TGSTIME[0:2], TGWTIME[0:2]
+  SETREG (0x9e, 0x00); // SENSOR_DEF
+
+  // RFHSET[0:4]: Refresh time of SDRAM in units of 2us
+  if (dev->model->model_id == MODEL_CANON_CANOSCAN_8600F)
+    {
+      SETREG(0xa2, 0x1f);
+    }
+
+  // 0xa6-0xa9: controls gpio, see gl843_gpio_init
+
+  // GPOM9, MULSTOP[0-2], NODECEL, TB3TB1, TB5TB2, FIX16CLK.
+  if (dev->model->model_id == MODEL_CANON_CANOSCAN_8600F)
+    {
+      SETREG(0xab, 0x00);
+    }
+
+  // VRHOME[3:2], VRMOVE[3:2], VRBACK[3:2]: Vref setting of the motor driver IC
+  // for various situations.
+  if (dev->model->model_id == MODEL_CANON_CANOSCAN_8600F)
+    {
+      SETREG(0xac, 0x00);
+    }
+
+  if (dev->model->model_id != MODEL_CANON_CANOSCAN_8400F)
+    {
+      SETREG (0x0c, 0x00);
+      SETREG (0x94, 0xff);
+      SETREG (0xab, 0x50);
+    }
+
+  if (dev->model->model_id != MODEL_CANON_CANOSCAN_4400F
+   && dev->model->model_id != MODEL_CANON_CANOSCAN_8400F)
+    {
+      SETREG (0xaa, 0x00);
+    }
+
+  /* G4050 values */
+  if (dev->model->model_id == MODEL_HP_SCANJET_G4010 ||
+      dev->model->model_id == MODEL_HP_SCANJET_G4050 ||
+      dev->model->model_id == MODEL_HP_SCANJET_4850C)
+    {
+      SETREG (0x03, 0x1d);
+      SETREG (0x06, 0xd0); /* SCANMOD=110, PWRBIT and no GAIN4 */
+      SETREG (0x06, 0xd8); /* SCANMOD=110, PWRBIT and GAIN4 */
+      SETREG (0x0a, 0x18);
+      SETREG (0x0b, 0x69);
+
+      /* CIS exposure is used for XPA lamp movement */
+      SETREG (0x10, 0x2c);
+      SETREG (0x11, 0x09);
+      SETREG (0x12, 0x22);
+      SETREG (0x13, 0xb8);
+      SETREG (0x14, 0x10);
+      SETREG (0x15, 0xf0);
+
+      SETREG (0x6b, 0xf4);
+
+      SETREG (0x70, 0x00);
+      SETREG (0x71, 0x02);
+      SETREG (0x72, 0x00);
+      SETREG (0x73, 0x00);
+
+      SETREG (0x80, 0x50);
+      SETREG (0x9d, 0x08);
+      SETREG (0xab, 0x40);
+
+      /* XXX STEF XXX TODO move to set for scan */
+      SETREG (0x98, 0x03);
+      SETREG (0x99, 0x30);
+      SETREG (0x9a, 0x01);
+      SETREG (0x9b, 0x80);
+      SETREG (0xac, 0x00);
+    }
+
+  if (dev->model->model_id == MODEL_CANON_CANOSCAN_4400F)
+    {
+      SETREG (0x06, 0xf0); /* SCANMOD=111, PWRBIT and no GAIN4 */
+      SETREG (0x0b, 0x69); /* 16M only */
+      SETREG (0x1e, 0x20);
+      SETREG (0x22, 0xc8);
+      SETREG (0x23, 0xc8);
+      SETREG (0x5e, 0x3f);
+      SETREG (0x5f, 0xf0);
+      SETREG (0x6b, 0x72);
+      SETREG (0x72, 0x01);
+      SETREG (0x73, 0x03);
+      SETREG (0x80, 0x0c);
+      SETREG (0x87, 0x02);      /* MCLOCK -> CK4MAP */
+      SETREG (0x9d, 0x08);      /* STEPTIM=2        */
+      SETREG (0xa2, 0x1f);
+      SETREG (0xab, 0x00);
+      sanei_genesys_set_double(&dev->reg,REG_EXPR,0x9c40);
+      sanei_genesys_set_double(&dev->reg,REG_EXPG,0x9c40);
+      sanei_genesys_set_double(&dev->reg,REG_EXPB,0x9c40);
+    }
+
+  if (dev->model->model_id == MODEL_CANON_CANOSCAN_8400F)
+    {
+      SETREG (0x03, 0x1c);
+      SETREG (0x06, 0xd0); /* SCANMOD=110, PWRBIT and no GAIN4 */
+      SETREG (0x0a, 0x10);
+      SETREG (0x22, 0x50);
+      SETREG (0x23, 0x50);
+      SETREG (0x5e, 0x85);
+      SETREG (0x6b, 0xb1);
+      SETREG (0x1e, 0xa0);
+      SETREG (0x72, 0x03);
+      SETREG (0x73, 0x04);
+      SETREG (0x7d, 0x20);
+      SETREG (0x80, 0x28);
+      SETREG (0x87, 0x02);      /* MCLOCK -> CK4MAP */
+      SETREG (0x9d, 0x08);      /* STEPTIM=2        */
+    }
+
+  dev->calib_reg = dev->reg;
+
+  DBGCOMPLETED;
+}
+
+/* Send slope table for motor movement
+   slope_table in machine byte order
+ */
+static SANE_Status
+gl843_send_slope_table (Genesys_Device * dev, int table_nr,
+			uint16_t * slope_table, int steps)
+{
+  SANE_Status status = SANE_STATUS_GOOD;
+  int i;
+  char msg[10000];
+
+  DBG(DBG_proc, "%s (table_nr = %d, steps = %d)\n", __func__, table_nr, steps);
+
+  std::vector<uint8_t> table(steps * 2);
+  for (i = 0; i < steps; i++)
+    {
+      table[i * 2] = slope_table[i] & 0xff;
+      table[i * 2 + 1] = slope_table[i] >> 8;
+    }
+
+  if (DBG_LEVEL >= DBG_io)
+    {
+      sprintf (msg, "write slope %d (%d)=", table_nr, steps);
+      for (i = 0; i < steps; i++)
+	{
+	  sprintf (msg+strlen(msg), "%d", slope_table[i]);
+	}
+      DBG(DBG_io, "%s: %s\n", __func__, msg);
+    }
+
+
+  /* slope table addresses are fixed : 0x4000,  0x4800,  0x5000,  0x5800,  0x6000 */
+  /* XXX STEF XXX USB 1.1 ? sanei_genesys_write_0x8c (dev, 0x0f, 0x14); */
+  status = write_data (dev, 0x4000 + 0x800 * table_nr, steps * 2, table.data());
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: write data failed writing slope table %d (%s)\n", __func__, table_nr,
+          sane_strstatus(status));
+    }
+
+  DBGCOMPLETED;
+  return status;
+}
+
+
+/* Set values of analog frontend */
+static SANE_Status
+gl843_set_fe (Genesys_Device * dev, const Genesys_Sensor& sensor, uint8_t set)
+{
+    (void) sensor;
+  SANE_Status status = SANE_STATUS_GOOD;
+  uint8_t val;
+  int i;
+
+  DBG(DBG_proc, "%s (%s)\n", __func__, set == AFE_INIT ? "init" : set == AFE_SET ? "set" : set ==
+      AFE_POWER_SAVE ? "powersave" : "huh?");
+
+  if (set == AFE_INIT)
+    {
+      DBG(DBG_proc, "%s(): setting DAC %u\n", __func__, dev->model->dac_type);
+      dev->frontend = dev->frontend_initial;
+    }
+
+  /* check analog frontend type */
+  // FIXME: looks like we write to that register with initial data
+  RIE (sanei_genesys_read_register (dev, REG04, &val));
+  if ((val & REG04_FESET) != 0x00)
+    {
+      /* for now there is no support for AD fe */
+      DBG(DBG_proc, "%s(): unsupported frontend type %d\n", __func__,
+          dev->reg.find_reg(0x04).value & REG04_FESET);
+      return SANE_STATUS_UNSUPPORTED;
+    }
+
+  DBG(DBG_proc, "%s(): frontend reset complete\n", __func__);
+
+  for (i = 1; i <= 3; i++)
+    {
+        // FIXME: BUG: we should initialize dev->frontend before first use. Right now it's
+        // initialized during genesys_coarse_calibration()
+        if (dev->frontend.regs.empty()) {
+            status = sanei_genesys_fe_write_data(dev, i, 0x00);
+        } else {
+            status = sanei_genesys_fe_write_data(dev, i, dev->frontend.regs.get_value(0x00 + i));
+        }
+      if (status != SANE_STATUS_GOOD)
+	{
+	  DBG(DBG_error, "%s: writing reg[%d] failed: %s\n", __func__, i, sane_strstatus(status));
+	  return status;
+	}
+    }
+    for (const auto& reg : sensor.custom_fe_regs) {
+        status = sanei_genesys_fe_write_data(dev, reg.address, reg.value);
+        if (status != SANE_STATUS_GOOD) {
+            DBG(DBG_error, "%s: writing reg[%d] failed: %s\n", __func__, i, sane_strstatus(status));
+            return status;
+        }
+    }
+
+  for (i = 0; i < 3; i++)
+    {
+        // FIXME: BUG: see above
+        if (dev->frontend.regs.empty()) {
+            status = sanei_genesys_fe_write_data(dev, 0x20 + i, 0x00);
+        } else {
+            status = sanei_genesys_fe_write_data(dev, 0x20 + i, dev->frontend.get_offset(i));
+        }
+      if (status != SANE_STATUS_GOOD)
+	{
+	  DBG(DBG_error, "%s: writing offset[%d] failed: %s\n", __func__, i,
+	      sane_strstatus(status));
+	  return status;
+	}
+    }
+
+  if (dev->model->ccd_type == CCD_KVSS080)
+    {
+      for (i = 0; i < 3; i++)
+	{
+            // FIXME: BUG: see above
+            if (dev->frontend.regs.empty()) {
+                status = sanei_genesys_fe_write_data(dev, 0x24 + i, 0x00);
+            } else {
+                status = sanei_genesys_fe_write_data(dev, 0x24 + i,
+                                                     dev->frontend.regs.get_value(0x24 + i));
+            }
+	  if (status != SANE_STATUS_GOOD)
+	    {
+	      DBG(DBG_error, "%s: writing sign[%d] failed: %s\n", __func__, i,
+		  sane_strstatus(status));
+	      return status;
+	    }
+	}
+    }
+
+  for (i = 0; i < 3; i++)
+    {
+        // FIXME: BUG: see above
+        if (dev->frontend.regs.empty()) {
+            status = sanei_genesys_fe_write_data(dev, 0x28 + i, 0x00);
+        } else {
+            status = sanei_genesys_fe_write_data(dev, 0x28 + i, dev->frontend.get_gain(i));
+        }
+      if (status != SANE_STATUS_GOOD)
+	{
+	  DBG(DBG_error, "%s: writing gain[%d] failed: %s\n", __func__, i, sane_strstatus(status));
+	  return status;
+	}
+    }
+
+  DBGCOMPLETED;
+  return SANE_STATUS_GOOD;
+}
+
+
+static SANE_Status
+gl843_init_motor_regs_scan (Genesys_Device * dev,
+                            const Genesys_Sensor& sensor,
+                            Genesys_Register_Set * reg,
+                            unsigned int exposure,
+			    float scan_yres,
+			    int scan_step_type,
+			    unsigned int scan_lines,
+			    unsigned int scan_dummy,
+			    unsigned int feed_steps,
+			    int scan_power_mode,
+                            unsigned int flags)
+{
+  SANE_Status status = SANE_STATUS_GOOD;
+  int use_fast_fed, coeff;
+  unsigned int lincnt;
+  uint16_t scan_table[1024];
+  uint16_t fast_table[1024];
+  int scan_steps,fast_steps, fast_step_type;
+  unsigned int feedl,factor,dist;
+  GenesysRegister *r;
+  uint32_t z1, z2;
+
+  DBGSTART;
+  DBG(DBG_info, "%s : exposure=%d, scan_yres=%g, scan_step_type=%d, scan_lines=%d, scan_dummy=%d, "
+      "feed_steps=%d, scan_power_mode=%d, flags=%x\n", __func__, exposure, scan_yres,
+      scan_step_type, scan_lines, scan_dummy, feed_steps, scan_power_mode, flags);
+
+  /* get step multiplier */
+  factor = gl843_get_step_multiplier (reg);
+
+  use_fast_fed = 0;
+
+  if((scan_yres>=300 && feed_steps>900) || (flags & MOTOR_FLAG_FEED))
+    use_fast_fed=1;
+
+  lincnt=scan_lines;
+  sanei_genesys_set_triple(reg,REG_LINCNT,lincnt);
+  DBG(DBG_io, "%s: lincnt=%d\n", __func__, lincnt);
+
+  /* compute register 02 value */
+  r = sanei_genesys_get_address (reg, REG02);
+  r->value = 0x00;
+  sanei_genesys_set_motor_power(*reg, true);
+
+  if (use_fast_fed)
+    r->value |= REG02_FASTFED;
+  else
+    r->value &= ~REG02_FASTFED;
+
+  /* in case of automatic go home, move until home sensor */
+  if (flags & MOTOR_FLAG_AUTO_GO_HOME)
+    r->value |= REG02_AGOHOME | REG02_NOTHOME;
+
+  /* disable backtracking */
+  if ((flags & MOTOR_FLAG_DISABLE_BUFFER_FULL_MOVE)
+      ||(scan_yres>=2400)
+      ||(scan_yres>=sensor.optical_res))
+    r->value |= REG02_ACDCDIS;
+
+  /* scan and backtracking slope table */
+  sanei_genesys_slope_table(scan_table,
+                            &scan_steps,
+                            scan_yres,
+                            exposure,
+                            dev->motor.base_ydpi,
+                            scan_step_type,
+                            factor,
+                            dev->model->motor_type,
+                            gl843_motors);
+  RIE(gl843_send_slope_table (dev, SCAN_TABLE, scan_table, scan_steps*factor));
+  RIE(gl843_send_slope_table (dev, BACKTRACK_TABLE, scan_table, scan_steps*factor));
+
+  /* STEPNO */
+  r = sanei_genesys_get_address (reg, REG_STEPNO);
+  r->value = scan_steps;
+
+  /* FSHDEC */
+  r = sanei_genesys_get_address (reg, REG_FSHDEC);
+  r->value = scan_steps;
+
+  /* fast table */
+  fast_step_type=0;
+  if(scan_step_type<=fast_step_type)
+    {
+      fast_step_type=scan_step_type;
+    }
+  sanei_genesys_slope_table(fast_table,
+                            &fast_steps,
+                            sanei_genesys_get_lowest_ydpi(dev),
+                            exposure,
+                            dev->motor.base_ydpi,
+                            fast_step_type,
+                            factor,
+                            dev->model->motor_type,
+                            gl843_motors);
+  RIE(gl843_send_slope_table (dev, STOP_TABLE, fast_table, fast_steps*factor));
+  RIE(gl843_send_slope_table (dev, FAST_TABLE, fast_table, fast_steps*factor));
+  RIE(gl843_send_slope_table (dev, HOME_TABLE, fast_table, fast_steps*factor));
+
+  /* FASTNO */
+  r = sanei_genesys_get_address (reg, REG_FASTNO);
+  r->value = fast_steps;
+
+  /* FMOVNO */
+  r = sanei_genesys_get_address (reg, REG_FMOVNO);
+  r->value = fast_steps;
+
+  /* substract acceleration distance from feedl */
+  feedl=feed_steps;
+  feedl<<=scan_step_type;
+
+  dist = scan_steps;
+  if (use_fast_fed)
+    {
+        dist += fast_steps*2;
+    }
+  DBG(DBG_io2, "%s: acceleration distance=%d\n", __func__, dist);
+
+  /* get sure when don't insane value : XXX STEF XXX in this case we should
+   * fall back to single table move */
+  if(dist<feedl)
+    feedl -= dist;
+  else
+    feedl = 1;
+
+  sanei_genesys_set_triple(reg,REG_FEEDL,feedl);
+  DBG(DBG_io, "%s: feedl=%d\n", __func__, feedl);
+
+  /* doesn't seem to matter that much */
+  sanei_genesys_calculate_zmode2 (use_fast_fed,
+				  exposure,
+				  scan_table,
+				  scan_steps,
+				  feedl,
+                                  scan_steps,
+                                  &z1,
+                                  &z2);
+  if(scan_yres>600)
+    {
+      z1=0;
+      z2=0;
+    }
+
+  sanei_genesys_set_triple(reg,REG_Z1MOD,z1);
+  DBG(DBG_info, "%s: z1 = %d\n", __func__, z1);
+
+  sanei_genesys_set_triple(reg,REG_Z2MOD,z2);
+  DBG(DBG_info, "%s: z2 = %d\n", __func__, z2);
+
+  r = sanei_genesys_get_address (reg, REG1E);
+  r->value &= 0xf0;		/* 0 dummy lines */
+  r->value |= scan_dummy;	/* dummy lines */
+
+  r = sanei_genesys_get_address (reg, REG67);
+  r->value = 0x3f | (scan_step_type << REG67S_STEPSEL);
+
+  r = sanei_genesys_get_address (reg, REG68);
+  r->value = 0x3f | (scan_step_type << REG68S_FSTPSEL);
+
+  /* steps for STOP table */
+  r = sanei_genesys_get_address (reg, REG_FMOVDEC);
+  r->value = fast_steps;
+
+  /* Vref XXX STEF XXX : optical divider or step type ? */
+  r = sanei_genesys_get_address (reg, 0x80);
+  if (!(dev->model->flags & GENESYS_FLAG_FULL_HWDPI_MODE))
+    {
+      r->value = 0x50;
+      coeff=sensor.optical_res/sanei_genesys_compute_dpihw(dev, sensor, scan_yres);
+      if (dev->model->motor_type == MOTOR_KVSS080)
+        {
+          if(coeff>=1)
+            {
+              r->value |= 0x05;
+            }
+        }
+      else {
+        switch(coeff)
+          {
+          case 4:
+              r->value |= 0x0a;
+              break;
+          case 2:
+              r->value |= 0x0f;
+              break;
+          case 1:
+              r->value |= 0x0f;
+              break;
+          }
+        }
+    }
+
+  DBGCOMPLETED;
+  return SANE_STATUS_GOOD;
+}
+
+
+/** @brief setup optical related registers
+ * start and pixels are expressed in optical sensor resolution coordinate
+ * space.
+ * @param dev device to use
+ * @param reg registers to set up
+ * @param exposure exposure time to use
+ * @param used_res scanning resolution used, may differ from
+ *        scan's one
+ * @param start logical start pixel coordinate
+ * @param pixels logical number of pixels to use
+ * @param channels number of color channles used (1 or 3)
+ * @param depth bit depth of the scan (1, 8 or 16 bits)
+ * @param ccd_size_divisor SANE_TRUE specifies how much x coordinates must be shrunk
+ * @param color_filter to choose the color channel used in gray scans
+ * @param flags to drive specific settings such no calibration, XPA use ...
+ * @return SANE_STATUS_GOOD if OK
+ */
+static SANE_Status
+gl843_init_optical_regs_scan (Genesys_Device * dev,
+                              const Genesys_Sensor& sensor,
+			      Genesys_Register_Set * reg,
+			      unsigned int exposure,
+			      int used_res,
+			      unsigned int start,
+			      unsigned int pixels,
+			      int channels,
+			      int depth,
+                              unsigned ccd_size_divisor,
+                              ColorFilter color_filter,
+                              int flags)
+{
+  unsigned int words_per_line;
+  unsigned int startx, endx, used_pixels;
+  unsigned int dpiset, dpihw, factor;
+  unsigned int bytes;
+  unsigned int tgtime;          /**> exposure time multiplier */
+  unsigned int cksel;           /**> clock per system pixel time in capturing image */
+  GenesysRegister *r;
+  SANE_Status status = SANE_STATUS_GOOD;
+
+  DBG(DBG_proc, "%s :  exposure=%d, used_res=%d, start=%d, pixels=%d, channels=%d, depth=%d, "
+      "ccd_size_divisor=%d, flags=%x\n", __func__, exposure, used_res, start, pixels, channels,
+      depth, ccd_size_divisor, flags);
+
+  /* tgtime */
+  tgtime = exposure / 65536 + 1;
+  DBG(DBG_io2, "%s: tgtime=%d\n", __func__, tgtime);
+
+  /* to manage high resolution device while keeping good
+   * low resolution scanning speed, we make hardware dpi vary */
+  dpihw=sanei_genesys_compute_dpihw(dev, sensor, used_res);
+  factor=sensor.optical_res/dpihw;
+  DBG(DBG_io2, "%s: dpihw=%d (factor=%d)\n", __func__, dpihw, factor);
+
+  /* sensor parameters */
+  gl843_setup_sensor (dev, sensor, reg, dpihw, flags);
+
+  /* resolution is divided according to CKSEL which is known once sensor is set up */
+  r = sanei_genesys_get_address (reg, REG18);
+  cksel= (r->value & REG18_CKSEL)+1;
+  DBG(DBG_io2, "%s: cksel=%d\n", __func__, cksel);
+  dpiset = used_res * cksel;
+
+  /* start and end coordinate in optical dpi coordinates */
+  startx = (start + sensor.dummy_pixel)/cksel;
+
+  used_pixels=pixels/cksel;
+  endx = startx + used_pixels;
+
+  /* pixel coordinate factor correction when used dpihw is not maximal one */
+  startx/=factor;
+  endx/=factor;
+  used_pixels=endx-startx;
+
+  /* in case of stagger we have to start at an odd coordinate */
+  if ((flags & OPTICAL_FLAG_STAGGER)
+      &&((startx & 1)==0))
+    {
+      startx++;
+      endx++;
+    }
+
+  status = gl843_set_fe(dev, sensor, AFE_SET);
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed to set frontend: %s\n", __func__, sane_strstatus(status));
+      return status;
+    }
+
+  /* enable shading */
+  r = sanei_genesys_get_address (reg, REG01);
+  r->value &= ~REG01_SCAN;
+  if ((flags & OPTICAL_FLAG_DISABLE_SHADING) || (dev->model->flags & GENESYS_FLAG_NO_CALIBRATION))
+    {
+      r->value &= ~REG01_DVDSET;
+    }
+  else
+    {
+      r->value |= REG01_DVDSET;
+    }
+  if(dpihw>600)
+    {
+      r->value |= REG01_SHDAREA;
+    }
+  else
+    {
+      r->value &= ~REG01_SHDAREA;
+    }
+
+  r = sanei_genesys_get_address (reg, REG03);
+  if (dev->model->model_id == MODEL_CANON_CANOSCAN_8600F)
+    r->value |= REG03_AVEENB;
+  else {
+    r->value &= ~REG03_AVEENB;
+  }
+
+    // FIXME: we probably don't need to set exposure to registers at this point. It was this way
+    // before a refactor.
+    sanei_genesys_set_lamp_power(dev, sensor, *reg, !(flags & OPTICAL_FLAG_DISABLE_LAMP));
+
+  /* select XPA */
+  r->value &= ~REG03_XPASEL;
+  if (flags & OPTICAL_FLAG_USE_XPA)
+    {
+      r->value |= REG03_XPASEL;
+    }
+    reg->state.is_xpa_on = flags & OPTICAL_FLAG_USE_XPA;
+
+  /* BW threshold */
+  r = sanei_genesys_get_address (reg, REG2E);
+  r->value = dev->settings.threshold;
+  r = sanei_genesys_get_address (reg, REG2F);
+  r->value = dev->settings.threshold;
+
+  /* monochrome / color scan */
+  r = sanei_genesys_get_address (reg, REG04);
+  switch (depth)
+    {
+    case 1:
+      r->value &= ~REG04_BITSET;
+      r->value |= REG04_LINEART;
+      break;
+    case 8:
+      r->value &= ~(REG04_LINEART | REG04_BITSET);
+      break;
+    case 16:
+      r->value &= ~REG04_LINEART;
+      r->value |= REG04_BITSET;
+      break;
+    }
+
+  r->value &= ~(REG04_FILTER | REG04_AFEMOD);
+  if (channels == 1)
+    {
+      switch (color_filter)
+	{
+            case ColorFilter::RED:
+                r->value |= 0x14;
+                break;
+            case ColorFilter::BLUE:
+                r->value |= 0x1c;
+                break;
+            case ColorFilter::GREEN:
+                r->value |= 0x18;
+                break;
+            default:
+                break; // should not happen
+	}
+    }
+  else
+    r->value |= 0x10;		/* mono */
+
+  /* register 05 */
+  r = sanei_genesys_get_address (reg, REG05);
+
+  /* set up dpihw */
+  r->value &= ~REG05_DPIHW;
+  switch(dpihw)
+    {
+      case 600:
+        r->value |= REG05_DPIHW_600;
+        break;
+      case 1200:
+        r->value |= REG05_DPIHW_1200;
+        break;
+      case 2400:
+        r->value |= REG05_DPIHW_2400;
+        break;
+      case 4800:
+        r->value |= REG05_DPIHW_4800;
+        break;
+    }
+
+  /* enable gamma tables */
+  if (flags & OPTICAL_FLAG_DISABLE_GAMMA)
+    r->value &= ~REG05_GMMENB;
+  else
+    r->value |= REG05_GMMENB;
+
+  sanei_genesys_set_double(reg, REG_DPISET, dpiset * ccd_size_divisor);
+  DBG(DBG_io2, "%s: dpiset used=%d\n", __func__, dpiset * ccd_size_divisor);
+
+  sanei_genesys_set_double(reg, REG_STRPIXEL, startx);
+  sanei_genesys_set_double(reg, REG_ENDPIXEL, endx);
+
+  /* words(16bit) before gamma, conversion to 8 bit or lineart */
+  words_per_line = (used_pixels * dpiset) / dpihw;
+  bytes = depth / 8;
+  if (depth == 1)
+    {
+      words_per_line = (words_per_line >> 3) + ((words_per_line & 7) ? 1 : 0);
+    }
+  else
+    {
+      words_per_line *= bytes;
+    }
+
+  dev->wpl = words_per_line;
+  dev->bpl = words_per_line;
+
+  DBG(DBG_io2, "%s: used_pixels=%d\n", __func__, used_pixels);
+  DBG(DBG_io2, "%s: pixels     =%d\n", __func__, pixels);
+  DBG(DBG_io2, "%s: depth      =%d\n", __func__, depth);
+  DBG(DBG_io2, "%s: dev->bpl   =%lu\n", __func__, (unsigned long) dev->bpl);
+  DBG(DBG_io2, "%s: dev->len   =%lu\n", __func__, (unsigned long)dev->len);
+  DBG(DBG_io2, "%s: dev->dist  =%lu\n", __func__, (unsigned long)dev->dist);
+
+  words_per_line *= channels;
+
+  /* MAXWD is expressed in 2 words unit */
+  /* nousedspace = (mem_bank_range * 1024 / 256 -1 ) * 4; */
+  sanei_genesys_set_triple(reg,REG_MAXWD,(words_per_line)>>1);
+  DBG(DBG_io2, "%s: words_per_line used=%d\n", __func__, words_per_line);
+
+  sanei_genesys_set_double(reg,REG_LPERIOD,exposure/tgtime);
+  DBG(DBG_io2, "%s: exposure used=%d\n", __func__, exposure/tgtime);
+
+  r = sanei_genesys_get_address (reg, REG_DUMMY);
+  r->value = sensor.dummy_pixel;
+
+  DBGCOMPLETED;
+  return SANE_STATUS_GOOD;
+}
+
+struct ScanSession {
+    SetupParams params;
+
+    // whether the session setup has been computed via gl843_compute_session()
+    bool computed = false;
+
+    // whether CCD operates as half-resolution or full resolution at a specific resolution
+    unsigned ccd_size_divisor = 1;
+
+    // the optical resolution of the scanner.
+    unsigned optical_resolution = 0;
+
+    // the number of pixels at the optical resolution.
+    unsigned optical_pixels = 0;
+
+    // the number of bytes in the output of a single line directly from scanner
+    unsigned optical_line_bytes = 0;
+
+    // the resolution of the output data.
+    unsigned output_resolution = 0;
+
+    // the number of pixels in output data
+    unsigned output_pixels = 0;
+
+    // the number of bytes in the output of a single line
+    unsigned output_line_bytes = 0;
+
+    // the number of lines in the output of the scanner. This must be larger than the user
+    // requested number due to line staggering and color channel shifting.
+    unsigned output_line_count = 0;
+
+    // the number of staggered lines (i.e. lines that overlap during scanning due to line being
+    // thinner than the CCD element)
+    unsigned num_staggered_lines = 0;
+
+    // the number of lines that color channels shift due to different physical positions of
+    // different color channels
+    unsigned max_color_shift_lines = 0;
+
+    void assert_computed() const
+    {
+        if (!computed) {
+            throw std::runtime_error("ScanSession is not computed");
+        }
+    }
+};
+
+static unsigned align_int_up(unsigned num, unsigned alignment)
+{
+    unsigned mask = alignment - 1;
+    if (num & mask)
+        num = (num & ~mask) + alignment;
+    return num;
+}
+
+// computes physical parameters for specific scan setup
+static void gl843_compute_session(Genesys_Device* dev, ScanSession& s,
+                                  const Genesys_Sensor& sensor)
+{
+    s.params.assert_valid();
+    s.ccd_size_divisor = sensor.get_ccd_size_divisor_for_dpi(s.params.xres);
+
+    s.optical_resolution = sensor.optical_res / s.ccd_size_divisor;
+
+    if (s.params.flags & SCAN_FLAG_USE_OPTICAL_RES) {
+        s.output_resolution = s.optical_resolution;
+    } else {
+        // resolution is choosen from a fixed list and can be used directly
+        // unless we have ydpi higher than sensor's maximum one
+        if (s.params.xres > s.optical_resolution)
+            s.output_resolution = s.optical_resolution;
+        else
+            s.output_resolution = s.params.xres;
+    }
+
+    // compute rounded up number of optical pixels
+    s.optical_pixels = (s.params.pixels * s.optical_resolution) / s.params.xres;
+    if (s.optical_pixels * s.params.xres < s.params.pixels * s.optical_resolution)
+        s.optical_pixels++;
+
+    // ensure the number of optical pixels is divisible by 2.
+    // In quarter-CCD mode optical_pixels is 4x larger than the actual physical number
+    s.optical_pixels = align_int_up(s.optical_pixels, 2 * s.ccd_size_divisor);
+
+    s.output_pixels =
+        (s.optical_pixels * s.output_resolution) / s.optical_resolution;
+
+    // Note: staggering is not applied for calibration. Staggering starts at 2400 dpi
+    s.num_staggered_lines = 0;
+    if ((s.params.yres > 1200) &&
+        ((s.params.flags & SCAN_FLAG_IGNORE_LINE_DISTANCE) == 0) &&
+        (dev->model->flags & GENESYS_FLAG_STAGGERED_LINE))
+    {
+        s.num_staggered_lines = (4 * s.params.yres) / dev->motor.base_ydpi;
+    }
+
+    s.max_color_shift_lines = sanei_genesys_compute_max_shift(dev, s.params.channels,
+                                                              s.params.yres, s.params.flags);
+
+    s.output_line_count = s.params.lines + s.max_color_shift_lines + s.num_staggered_lines;
+
+    s.optical_line_bytes = (s.optical_pixels * s.params.channels * s.params.depth) / 8;
+    s.output_line_bytes = (s.output_pixels * s.params.channels * s.params.depth) / 8;
+    s.computed = true;
+}
+
+/* set up registers for an actual scan
+ *
+ * this function sets up the scanner to scan in normal or single line mode
+ */
+static SANE_Status gl843_init_scan_regs(Genesys_Device* dev, const Genesys_Sensor& sensor,
+                                        Genesys_Register_Set* reg,
+                                        ScanSession& session)
+{
+    session.assert_computed();
+
+  int start;
+  int move;
+  unsigned int oflags, mflags;  /**> optical and motor flags */
+  int exposure;
+
+  int slope_dpi = 0;
+  int dummy = 0;
+  int scan_step_type = 1;
+  int scan_power_mode = 0;
+  size_t requested_buffer_size, read_buffer_size;
+
+  SANE_Status status = SANE_STATUS_GOOD;
+
+    DBG(DBG_info, "%s ", __func__);
+    debug_dump(DBG_info, session.params);
+
+  DBG(DBG_info, "%s : stagger=%d lines\n", __func__, session.num_staggered_lines);
+
+  /* we enable true gray for cis scanners only, and just when doing
+   * scan since color calibration is OK for this mode
+   */
+  oflags = 0;
+  if (session.params.flags & SCAN_FLAG_DISABLE_SHADING)
+    oflags |= OPTICAL_FLAG_DISABLE_SHADING;
+  if (session.params.flags & SCAN_FLAG_DISABLE_GAMMA)
+    oflags |= OPTICAL_FLAG_DISABLE_GAMMA;
+  if (session.params.flags & SCAN_FLAG_DISABLE_LAMP)
+    oflags |= OPTICAL_FLAG_DISABLE_LAMP;
+  if (session.params.flags & SCAN_FLAG_CALIBRATION)
+    oflags |= OPTICAL_FLAG_DISABLE_DOUBLE;
+  if (session.num_staggered_lines)
+    oflags |= OPTICAL_FLAG_STAGGER;
+  if (session.params.flags & SCAN_FLAG_USE_XPA)
+    oflags |= OPTICAL_FLAG_USE_XPA;
+
+
+  /* compute scan parameters values */
+  /* pixels are allways given at full optical resolution */
+  /* use detected left margin and fixed value */
+  /* start */
+  start = session.params.startx;
+
+  dummy = 0;
+  /* dummy = 1;  XXX STEF XXX */
+
+  /* slope_dpi */
+  /* cis color scan is effectively a gray scan with 3 gray lines per color line and a FILTER of 0 */
+  if (dev->model->is_cis)
+    slope_dpi = session.params.yres * session.params.channels;
+  else
+    slope_dpi = session.params.yres;
+  slope_dpi = slope_dpi * (1 + dummy);
+
+  /* scan_step_type */
+  exposure = sensor.exposure_lperiod;
+  if (exposure < 0) {
+      throw std::runtime_error("Exposure not defined in sensor definition");
+  }
+  scan_step_type = sanei_genesys_compute_step_type(gl843_motors, dev->model->motor_type, exposure);
+
+  DBG(DBG_info, "%s : exposure=%d pixels\n", __func__, exposure);
+  DBG(DBG_info, "%s : scan_step_type=%d\n", __func__, scan_step_type);
+
+  /*** optical parameters ***/
+  /* in case of dynamic lineart, we use an internal 8 bit gray scan
+   * to generate 1 lineart data */
+    if (session.params.flags & SCAN_FLAG_DYNAMIC_LINEART) {
+        session.params.depth = 8;
+    }
+
+  /* no 16 bit gamma for this ASIC */
+  if (session.params.depth == 16)
+    {
+      session.params.flags |= SCAN_FLAG_DISABLE_GAMMA;
+      oflags |= OPTICAL_FLAG_DISABLE_GAMMA;
+    }
+
+  /* now _LOGICAL_ optical values used are known, setup registers */
+  status = gl843_init_optical_regs_scan (dev, sensor,
+                                         reg,
+					 exposure,
+                                         session.output_resolution,
+					 start,
+                                         session.optical_pixels,
+                                         session.params.channels,
+                                         session.params.depth,
+                                         session.ccd_size_divisor,
+                                         session.params.color_filter,
+                                         oflags);
+  if (status != SANE_STATUS_GOOD)
+    return status;
+
+  /*** motor parameters ***/
+
+  /* it seems base_dpi of the G4050 motor is changed above 600 dpi*/
+  if (dev->model->motor_type == MOTOR_G4050 && session.params.yres>600)
+    {
+      dev->ld_shift_r = (dev->model->ld_shift_r*3800)/dev->motor.base_ydpi;
+      dev->ld_shift_g = (dev->model->ld_shift_g*3800)/dev->motor.base_ydpi;
+      dev->ld_shift_b = (dev->model->ld_shift_b*3800)/dev->motor.base_ydpi;
+    }
+  else
+    {
+      dev->ld_shift_r = dev->model->ld_shift_r;
+      dev->ld_shift_g = dev->model->ld_shift_g;
+      dev->ld_shift_b = dev->model->ld_shift_b;
+    }
+
+  /* add tl_y to base movement */
+  move = session.params.starty;
+  DBG(DBG_info, "%s: move=%d steps\n", __func__, move);
+
+
+  mflags=0;
+  if(session.params.flags & SCAN_FLAG_DISABLE_BUFFER_FULL_MOVE)
+    mflags|=MOTOR_FLAG_DISABLE_BUFFER_FULL_MOVE;
+  if(session.params.flags & SCAN_FLAG_FEEDING)
+    mflags|=MOTOR_FLAG_FEED;
+  if (session.params.flags & SCAN_FLAG_USE_XPA)
+    mflags |= MOTOR_FLAG_USE_XPA;
+
+  status = gl843_init_motor_regs_scan (dev, sensor,
+                                       reg,
+                                       exposure,
+                                       slope_dpi,
+                                       scan_step_type,
+                                       dev->model->is_cis ? session.output_line_count * session.params.channels
+                                                          : session.output_line_count,
+                                       dummy,
+                                       move,
+                                       scan_power_mode,
+                                       mflags);
+  if (status != SANE_STATUS_GOOD)
+    return status;
+
+  /* since we don't have sheetfed scanners to handle,
+   * use huge read buffer */
+  /* TODO find the best size according to settings */
+  requested_buffer_size = 16 * session.output_line_bytes;
+
+  read_buffer_size =
+    2 * requested_buffer_size +
+    (session.max_color_shift_lines + session.num_staggered_lines) * session.optical_line_bytes;
+
+    dev->read_buffer.clear();
+    dev->read_buffer.alloc(read_buffer_size);
+
+    dev->lines_buffer.clear();
+    dev->lines_buffer.alloc(read_buffer_size);
+
+    dev->shrink_buffer.clear();
+    dev->shrink_buffer.alloc(requested_buffer_size);
+
+    dev->out_buffer.clear();
+    dev->out_buffer.alloc((8 * session.params.pixels * session.params.channels *
+                           session.params.depth) / 8);
+
+  dev->read_bytes_left = session.output_line_bytes * session.output_line_count;
+
+  DBG(DBG_info, "%s: physical bytes to read = %lu\n", __func__, (u_long) dev->read_bytes_left);
+  dev->read_active = SANE_TRUE;
+
+  dev->current_setup.params = session.params;
+  dev->current_setup.pixels = session.output_pixels;
+  DBG(DBG_info, "%s: current_setup.pixels=%d\n", __func__, dev->current_setup.pixels);
+  dev->current_setup.lines = session.output_line_count;
+  dev->current_setup.depth = session.params.depth;
+  dev->current_setup.channels = session.params.channels;
+  dev->current_setup.exposure_time = exposure;
+  dev->current_setup.xres = session.output_resolution;
+  dev->current_setup.yres = session.params.yres;
+  dev->current_setup.ccd_size_divisor = session.ccd_size_divisor;
+  dev->current_setup.stagger = session.num_staggered_lines;
+  dev->current_setup.max_shift = session.max_color_shift_lines + session.num_staggered_lines;
+
+  dev->total_bytes_read = 0;
+    if (session.params.depth == 1) {
+        dev->total_bytes_to_read = ((session.params.pixels * session.params.lines) / 8 +
+            (((session.params.pixels * session.params.lines) % 8) ? 1 : 0)) *
+                session.params.channels;
+    } else {
+        dev->total_bytes_to_read = session.params.pixels * session.params.lines *
+                session.params.channels * (session.params.depth / 8);
+    }
+
+  DBG(DBG_info, "%s: total bytes to send = %lu\n", __func__, (u_long) dev->total_bytes_to_read);
+
+  DBG(DBG_proc, "%s: completed\n", __func__);
+  return SANE_STATUS_GOOD;
+}
+
+static void
+gl843_calculate_current_setup(Genesys_Device * dev, const Genesys_Sensor& sensor)
+{
+  int channels;
+  int depth;
+  int start;
+
+  int used_res;
+  int used_pixels;
+  unsigned int lincnt;
+  int exposure;
+  int stagger;
+
+  int max_shift;
+
+  int optical_res;
+
+    DBG(DBG_info, "%s ", __func__);
+    debug_dump(DBG_info, dev->settings);
+
+  /* we have 2 domains for ccd: xres below or above half ccd max dpi */
+  unsigned ccd_size_divisor = sensor.get_ccd_size_divisor_for_dpi(dev->settings.xres);
+
+  /* channels */
+  if (dev->settings.scan_mode == ScanColorMode::COLOR_SINGLE_PASS)
+    channels = 3;
+  else
+    channels = 1;
+
+  /* depth */
+  depth = dev->settings.depth;
+  if (dev->settings.scan_mode == ScanColorMode::LINEART)
+    depth = 1;
+
+  /* start */
+  if(dev->settings.scan_method==ScanMethod::TRANSPARENCY)
+      start = SANE_UNFIX (dev->model->x_offset_ta);
+  else
+      start = SANE_UNFIX (dev->model->x_offset);
+
+  start /= ccd_size_divisor;
+
+  start += dev->settings.tl_x;
+  start = (start * sensor.optical_res) / MM_PER_INCH;
+
+    SetupParams params;
+    params.xres = dev->settings.xres;
+    params.yres = dev->settings.yres;
+    params.startx = start; // not used
+    params.starty = 0; // not used
+    params.pixels = dev->settings.pixels;
+    params.lines = dev->settings.lines;
+    params.depth = depth;
+    params.channels = channels;
+    params.scan_method = dev->settings.scan_method;
+    params.scan_mode = dev->settings.scan_mode;
+    params.color_filter = dev->settings.color_filter;
+    params.flags = 0;
+
+    DBG(DBG_info, "%s ", __func__);
+    debug_dump(DBG_info, params);
+
+  /* optical_res */
+  optical_res = sensor.optical_res / ccd_size_divisor;
+
+  /* stagger */
+  if (ccd_size_divisor == 1 && (dev->model->flags & GENESYS_FLAG_STAGGERED_LINE))
+    stagger = (4 * params.yres) / dev->motor.base_ydpi;
+  else
+    stagger = 0;
+  DBG(DBG_info, "%s: stagger=%d lines\n", __func__, stagger);
+
+    if (params.xres <= (unsigned) optical_res) {
+        used_res = params.xres;
+    } else {
+        used_res = optical_res;
+    }
+
+  /* compute scan parameters values */
+  /* pixels are allways given at half or full CCD optical resolution */
+  /* use detected left margin  and fixed value */
+
+  /* compute correct pixels number */
+  used_pixels = (params.pixels * optical_res) / params.xres;
+  DBG(DBG_info, "%s: used_pixels=%d\n", __func__, used_pixels);
+
+  /* exposure */
+  exposure = sensor.exposure_lperiod;
+  if (exposure < 0) {
+      throw std::runtime_error("Exposure not defined in sensor definition");
+  }
+  DBG(DBG_info, "%s : exposure=%d pixels\n", __func__, exposure);
+
+  /* it seems base_dpi of the G4050 motor is changed above 600 dpi*/
+  if (dev->model->motor_type == MOTOR_G4050 && params.yres>600)
+    {
+      dev->ld_shift_r = (dev->model->ld_shift_r*3800)/dev->motor.base_ydpi;
+      dev->ld_shift_g = (dev->model->ld_shift_g*3800)/dev->motor.base_ydpi;
+      dev->ld_shift_b = (dev->model->ld_shift_b*3800)/dev->motor.base_ydpi;
+    }
+  else
+    {
+      dev->ld_shift_r = dev->model->ld_shift_r;
+      dev->ld_shift_g = dev->model->ld_shift_g;
+      dev->ld_shift_b = dev->model->ld_shift_b;
+    }
+
+  /* scanned area must be enlarged by max color shift needed */
+    max_shift = sanei_genesys_compute_max_shift(dev, params.channels, params.yres, 0);
+
+  /* lincnt */
+  lincnt = params.lines + max_shift + stagger;
+
+  dev->current_setup.params = params;
+  dev->current_setup.pixels = (used_pixels * used_res) / optical_res;
+  DBG(DBG_info, "%s: current_setup.pixels=%d\n", __func__, dev->current_setup.pixels);
+  dev->current_setup.lines = lincnt;
+  dev->current_setup.depth = params.depth;
+  dev->current_setup.channels = params.channels;
+  dev->current_setup.exposure_time = exposure;
+  dev->current_setup.xres = used_res;
+  dev->current_setup.yres = params.yres;
+  dev->current_setup.ccd_size_divisor = ccd_size_divisor;
+  dev->current_setup.stagger = stagger;
+  dev->current_setup.max_shift = max_shift + stagger;
+
+  DBG(DBG_proc, "%s: completed\n", __func__);
+}
+
+/**
+ * for fast power saving methods only, like disabling certain amplifiers
+ * @param dev device to use
+ * @param enable true to set inot powersaving
+ * */
+static SANE_Status
+gl843_save_power (Genesys_Device * dev, SANE_Bool enable)
+{
+  uint8_t val;
+  SANE_Status status = SANE_STATUS_GOOD;
+
+  DBG(DBG_proc, "%s: enable = %d\n", __func__, enable);
+  if (dev == NULL)
+    return SANE_STATUS_INVAL;
+
+  /* switch KV-SS080 lamp off */
+  if (dev->model->gpo_type == GPO_KVSS080)
+    {
+      RIE(sanei_genesys_read_register (dev, REG6C, &val));
+      if(enable)
+        val &= 0xef;
+      else
+        val |= 0x10;
+      RIE(sanei_genesys_write_register(dev,REG6C,val));
+    }
+
+  DBGCOMPLETED;
+  return SANE_STATUS_GOOD;
+}
+
+static SANE_Status
+gl843_set_powersaving (Genesys_Device * dev, int delay /* in minutes */ )
+{
+  SANE_Status status = SANE_STATUS_GOOD;
+
+  DBG(DBG_proc, "%s (delay = %d)\n", __func__, delay);
+  if (dev == NULL)
+    return SANE_STATUS_INVAL;
+
+  DBGCOMPLETED;
+  return status;
+}
+
+static SANE_Status
+gl843_start_action (Genesys_Device * dev)
+{
+  return sanei_genesys_write_register (dev, 0x0f, 0x01);
+}
+
+static SANE_Status
+gl843_stop_action_no_move(Genesys_Device* dev, Genesys_Register_Set* reg)
+{
+    uint8_t val = sanei_genesys_read_reg_from_set(reg, REG01);
+    val &= ~REG01_SCAN;
+    sanei_genesys_set_reg_from_set(reg, REG01, val);
+    SANE_Status ret = sanei_genesys_write_register(dev, REG01, val);
+    sanei_genesys_sleep_ms(100);
+    return ret;
+}
+
+static SANE_Status
+gl843_stop_action (Genesys_Device * dev)
+{
+  SANE_Status status = SANE_STATUS_GOOD;
+  uint8_t val40, val;
+  unsigned int loop;
+
+  DBG(DBG_proc, "%s\n", __func__);
+
+  status = sanei_genesys_get_status (dev, &val);
+  if (DBG_LEVEL >= DBG_io)
+    {
+      sanei_genesys_print_status (val);
+    }
+
+  val40 = 0;
+  status = sanei_genesys_read_register (dev, REG40, &val40);
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed to read home sensor: %s\n", __func__, sane_strstatus(status));
+      DBG(DBG_proc, "%s: completed\n", __func__);
+      return status;
+    }
+
+  /* only stop action if needed */
+  if (!(val40 & REG40_DATAENB) && !(val40 & REG40_MOTMFLG))
+    {
+      DBG(DBG_info, "%s: already stopped\n", __func__);
+      DBG(DBG_proc, "%s: completed\n", __func__);
+      return SANE_STATUS_GOOD;
+    }
+
+  /* ends scan 646  */
+  val = dev->reg.get8(REG01);
+  val &= ~REG01_SCAN;
+  dev->reg.set8(REG01, val);
+  status = sanei_genesys_write_register (dev, REG01, val);
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed to write register 01: %s\n", __func__, sane_strstatus(status));
+      return status;
+    }
+  sanei_genesys_sleep_ms(100);
+
+  loop = 10;
+  while (loop > 0)
+    {
+      status = sanei_genesys_get_status (dev, &val);
+      if (DBG_LEVEL >= DBG_io)
+	{
+	  sanei_genesys_print_status (val);
+	}
+      val40 = 0;
+      status = sanei_genesys_read_register (dev, 0x40, &val40);
+      if (status != SANE_STATUS_GOOD)
+	{
+	  DBG(DBG_error, "%s: failed to read home sensor: %s\n", __func__, sane_strstatus(status));
+	  DBGCOMPLETED;
+	  return status;
+	}
+
+      /* if scanner is in command mode, we are done */
+      if (!(val40 & REG40_DATAENB) && !(val40 & REG40_MOTMFLG)
+	  && !(val & REG41_MOTORENB))
+	{
+	  DBGCOMPLETED;
+	  return SANE_STATUS_GOOD;
+	}
+
+      sanei_genesys_sleep_ms(100);
+      loop--;
+    }
+
+  DBGCOMPLETED;
+  return SANE_STATUS_IO_ERROR;
+}
+
+static SANE_Status
+gl843_get_paper_sensor (Genesys_Device * dev, SANE_Bool * paper_loaded)
+{
+  SANE_Status status = SANE_STATUS_GOOD;
+  uint8_t val;
+
+  status = sanei_genesys_read_register (dev, REG6D, &val);
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed to read gpio: %s\n", __func__, sane_strstatus(status));
+      return status;
+    }
+  *paper_loaded = (val & 0x1) == 0;
+  return SANE_STATUS_GOOD;
+
+  return SANE_STATUS_INVAL;
+}
+
+static SANE_Status
+gl843_eject_document (Genesys_Device * dev)
+{
+  DBG(DBG_proc, "%s: not implemented \n", __func__);
+  if (dev == NULL)
+    return SANE_STATUS_INVAL;
+  return SANE_STATUS_GOOD;
+}
+
+
+static SANE_Status
+gl843_load_document (Genesys_Device * dev)
+{
+  DBG(DBG_proc, "%s: not implemented \n", __func__);
+  if (dev == NULL)
+    return SANE_STATUS_INVAL;
+  return SANE_STATUS_GOOD;
+}
+
+/**
+ * detects end of document and adjust current scan
+ * to take it into account
+ * used by sheetfed scanners
+ */
+static SANE_Status
+gl843_detect_document_end (Genesys_Device * dev)
+{
+  SANE_Status status = SANE_STATUS_GOOD;
+  SANE_Bool paper_loaded;
+  unsigned int scancnt = 0;
+  int flines, channels, depth, bytes_remain, sublines,
+    bytes_to_flush, lines, sub_bytes, tmp, read_bytes_left;
+  DBG(DBG_proc, "%s: begin\n", __func__);
+
+  RIE (gl843_get_paper_sensor (dev, &paper_loaded));
+
+  /* sheetfed scanner uses home sensor as paper present */
+  if ((dev->document == SANE_TRUE) && !paper_loaded)
+    {
+      DBG(DBG_info, "%s: no more document\n", __func__);
+      dev->document = SANE_FALSE;
+
+      channels = dev->current_setup.channels;
+      depth = dev->current_setup.depth;
+      read_bytes_left = (int) dev->read_bytes_left;
+      DBG(DBG_io, "%s: read_bytes_left=%d\n", __func__, read_bytes_left);
+
+      /* get lines read */
+        try {
+            status = sanei_genesys_read_scancnt(dev, &scancnt);
+        } catch (...) {
+            flines = 0;
+        }
+      if (status != SANE_STATUS_GOOD)
+	{
+	  flines = 0;
+	}
+      else
+	{
+	  /* compute number of line read */
+	  tmp = (int) dev->total_bytes_read;
+          if (depth == 1 || dev->settings.scan_mode == ScanColorMode::LINEART)
+	    flines = tmp * 8 / dev->settings.pixels / channels;
+	  else
+	    flines = tmp / (depth / 8) / dev->settings.pixels / channels;
+
+	  /* number of scanned lines, but no read yet */
+	  flines = scancnt - flines;
+
+	  DBG(DBG_io, "%s: %d scanned but not read lines\n", __func__, flines);
+	}
+
+      /* adjust number of bytes to read
+       * we need to read the final bytes which are word per line * number of last lines
+       * to have doc leaving feeder */
+      lines =
+	(SANE_UNFIX (dev->model->post_scan) * dev->current_setup.yres) /
+	MM_PER_INCH + flines;
+      DBG(DBG_io, "%s: adding %d line to flush\n", __func__, lines);
+
+      /* number of bytes to read from scanner to get document out of it after
+       * end of document dectected by hardware sensor */
+      bytes_to_flush = lines * dev->wpl;
+
+      /* if we are already close to end of scan, flushing isn't needed */
+      if (bytes_to_flush < read_bytes_left)
+	{
+	  /* we take all these step to work around an overflow on some plateforms */
+	  tmp = (int) dev->total_bytes_read;
+	  DBG (DBG_io, "%s: tmp=%d\n", __func__, tmp);
+	  bytes_remain = (int) dev->total_bytes_to_read;
+	  DBG(DBG_io, "%s: bytes_remain=%d\n", __func__, bytes_remain);
+	  bytes_remain = bytes_remain - tmp;
+	  DBG(DBG_io, "%s: bytes_remain=%d\n", __func__, bytes_remain);
+
+	  /* remaining lines to read by frontend for the current scan */
+          if (depth == 1 || dev->settings.scan_mode == ScanColorMode::LINEART)
+	    {
+	      flines = bytes_remain * 8 / dev->settings.pixels / channels;
+	    }
+	  else
+	    flines = bytes_remain / (depth / 8)
+	      / dev->settings.pixels / channels;
+	  DBG(DBG_io, "%s: flines=%d\n", __func__, flines);
+
+	  if (flines > lines)
+	    {
+	      /* change the value controlling communication with the frontend :
+	       * total bytes to read is current value plus the number of remaining lines
+	       * multiplied by bytes per line */
+	      sublines = flines - lines;
+
+              if (depth == 1 || dev->settings.scan_mode == ScanColorMode::LINEART)
+		sub_bytes =
+		  ((dev->settings.pixels * sublines) / 8 +
+		   (((dev->settings.pixels * sublines) % 8) ? 1 : 0)) *
+		  channels;
+	      else
+		sub_bytes =
+		  dev->settings.pixels * sublines * channels * (depth / 8);
+
+	      dev->total_bytes_to_read -= sub_bytes;
+
+	      /* then adjust the physical bytes to read */
+	      if (read_bytes_left > sub_bytes)
+		{
+		  dev->read_bytes_left -= sub_bytes;
+		}
+	      else
+		{
+		  dev->total_bytes_to_read = dev->total_bytes_read;
+		  dev->read_bytes_left = 0;
+		}
+
+	      DBG(DBG_io, "%s: sublines=%d\n", __func__, sublines);
+	      DBG(DBG_io, "%s: subbytes=%d\n", __func__, sub_bytes);
+	      DBG(DBG_io, "%s: total_bytes_to_read=%lu\n", __func__,
+		  (unsigned long) dev->total_bytes_to_read);
+	      DBG(DBG_io, "%s: read_bytes_left=%d\n", __func__, read_bytes_left);
+	    }
+	}
+      else
+	{
+	  DBG(DBG_io, "%s: no flushing needed\n", __func__);
+	}
+    }
+
+  DBG(DBG_proc, "%s: finished\n", __func__);
+  return SANE_STATUS_GOOD;
+}
+
+// enables or disables XPA slider motor
+static SANE_Status gl843_set_xpa_motor_power(Genesys_Device *dev, bool set)
+{
+    uint8_t val;
+    SANE_Status status=SANE_STATUS_GOOD;
+
+    DBGSTART;
+
+    if (dev->model->model_id == MODEL_CANON_CANOSCAN_8600F) {
+
+        if (set) {
+            RIE(sanei_genesys_read_register(dev, REG6C, &val));
+            val &= ~REG6C_GPIO14;
+            if (dev->current_setup.xres >= 2400) {
+                val |= REG6C_GPIO10;
+            }
+            RIE(sanei_genesys_write_register(dev, REG6C, val));
+
+            RIE(sanei_genesys_read_register(dev, REGA6, &val));
+            val |= REGA6_GPIO17;
+            RIE(sanei_genesys_write_register(dev, REGA6,val));
+        } else {
+            RIE(sanei_genesys_read_register(dev, REG6C, &val));
+            val |= REG6C_GPIO14;
+            val &= ~REG6C_GPIO10;
+            RIE(sanei_genesys_write_register(dev, REG6C, val));
+
+            RIE(sanei_genesys_read_register(dev, REGA6, &val));
+            val &= ~REGA6_GPIO17;
+            RIE(sanei_genesys_write_register(dev, REGA6,val));
+        }
+        DBGCOMPLETED;
+        return status;
+    }
+
+    if (dev->model->model_id == MODEL_HP_SCANJET_G4050) {
+
+        if (set) {
+            /* set MULTFILM et GPOADF */
+            RIE (sanei_genesys_read_register (dev, REG6B, &val));
+            val |=REG6B_MULTFILM|REG6B_GPOADF;
+            RIE (sanei_genesys_write_register (dev, REG6B, val));
+
+            RIE (sanei_genesys_read_register (dev, REG6C, &val));
+            val &= ~REG6C_GPIO15;
+            RIE (sanei_genesys_write_register (dev, REG6C, val));
+
+            /* Motor power ? No move at all without this one */
+            RIE (sanei_genesys_read_register (dev, REGA6, &val));
+            val |= REGA6_GPIO20;
+            RIE (sanei_genesys_write_register(dev,REGA6,val));
+
+            RIE (sanei_genesys_read_register (dev, REGA8, &val));
+            val &= ~REGA8_GPO27;
+            RIE (sanei_genesys_write_register (dev, REGA8, val));
+
+            RIE (sanei_genesys_read_register (dev, REGA9, &val));
+            val |= REGA9_GPO32|REGA9_GPO31;
+            RIE (sanei_genesys_write_register (dev, REGA9, val));
+        } else {
+            /* unset GPOADF */
+            RIE (sanei_genesys_read_register (dev, REG6B, &val));
+            val &= ~REG6B_GPOADF;
+            RIE (sanei_genesys_write_register (dev, REG6B, val));
+
+            RIE (sanei_genesys_read_register (dev, REGA8, &val));
+            val |= REGA8_GPO27;
+            RIE (sanei_genesys_write_register (dev, REGA8, val));
+
+            RIE (sanei_genesys_read_register (dev, REGA9, &val));
+            val &= ~REGA9_GPO31;
+            RIE (sanei_genesys_write_register (dev, REGA9, val));
+        }
+        DBGCOMPLETED;
+        return status;
+    }
+
+    DBGCOMPLETED;
+    return status;
+}
+
+
+/** @brief light XPA lamp
+ * toggle gpios to switch off regular lamp and light on the
+ * XPA light
+ * @param dev device to set up
+ */
+static SANE_Status gl843_set_xpa_lamp_power(Genesys_Device *dev, bool set)
+{
+    SANE_Status status = SANE_STATUS_GOOD;
+    uint8_t val = 0;
+    DBGSTART;
+
+    if (set) {
+        RIE(sanei_genesys_read_register(dev, REGA6, &val));
+
+        // cut regular lamp power
+        val &= ~(REGA6_GPIO24 | REGA6_GPIO23);
+
+        // set XPA lamp power
+        val |= REGA6_GPIO22 | REGA6_GPIO21 | REGA6_GPIO19;
+
+        RIE(sanei_genesys_write_register(dev, REGA6, val));
+
+        RIE(sanei_genesys_read_register(dev, REGA7, &val));
+        val|=REGA7_GPOE24; /* lamp 1 off GPOE 24 */
+        val|=REGA7_GPOE23; /* lamp 2 off GPOE 23 */
+        val|=REGA7_GPOE22; /* full XPA lamp power */
+        RIE(sanei_genesys_write_register(dev, REGA7, val));
+    } else {
+        RIE(sanei_genesys_read_register(dev, REGA6, &val));
+
+        // switch on regular lamp
+        val |= REGA6_GPIO23;
+
+        // no XPA lamp power (2 bits for level: __11 ____)
+        val &= ~(REGA6_GPIO22 | REGA6_GPIO21);
+
+        RIE(sanei_genesys_write_register(dev, REGA6, val));
+    }
+
+    DBGCOMPLETED;
+    return status;
+}
+
+/* Send the low-level scan command */
+static SANE_Status
+gl843_begin_scan (Genesys_Device * dev, const Genesys_Sensor& sensor, Genesys_Register_Set * reg,
+		  SANE_Bool start_motor)
+{
+  SANE_Status status = SANE_STATUS_GOOD;
+  uint8_t val;
+  uint16_t dpiset, dpihw;
+
+  DBGSTART;
+
+  /* get back the target dpihw */
+  sanei_genesys_get_double (reg, REG_DPISET, &dpiset);
+  dpihw = sanei_genesys_compute_dpihw(dev, sensor, dpiset);
+
+  /* set up GPIO for scan */
+  switch(dev->model->gpo_type)
+    {
+      /* KV case */
+      case GPO_KVSS080:
+        RIE (sanei_genesys_write_register (dev, REGA9, 0x00));
+        RIE (sanei_genesys_write_register (dev, REGA6, 0xf6));
+        /* blinking led */
+        RIE (sanei_genesys_write_register (dev, 0x7e, 0x04));
+        break;
+      case GPO_G4050:
+        RIE (sanei_genesys_write_register (dev, REGA7, 0xfe));
+        RIE (sanei_genesys_write_register (dev, REGA8, 0x3e));
+        RIE (sanei_genesys_write_register (dev, REGA9, 0x06));
+        switch (dpihw)
+	  {
+	   case 1200:
+	   case 2400:
+	   case 4800:
+	     RIE (sanei_genesys_write_register (dev, REG6C, 0x60));
+	     RIE (sanei_genesys_write_register (dev, REGA6, 0x46));
+	     break;
+	   default:		/* 600 dpi  case */
+	     RIE (sanei_genesys_write_register (dev, REG6C, 0x20));
+	     RIE (sanei_genesys_write_register (dev, REGA6, 0x44));
+	  }
+
+            if (reg->state.is_xpa_on && reg->state.is_lamp_on) {
+                RIE(gl843_set_xpa_lamp_power(dev, true));
+            }
+
+            if (reg->state.is_xpa_on) {
+                dev->needs_home_ta = SANE_TRUE;
+                RIE(gl843_set_xpa_motor_power(dev, true));
+            }
+
+        /* blinking led */
+        RIE (sanei_genesys_write_register (dev, REG7E, 0x01));
+        break;
+      case GPO_CS8600F:
+            if (reg->state.is_xpa_on) {
+                dev->needs_home_ta = SANE_TRUE;
+                RIE(gl843_set_xpa_motor_power(dev, true));
+            }
+        break;
+      case GPO_CS4400F:
+      case GPO_CS8400F:
+      default:
+        break;
+    }
+
+  /* clear scan and feed count */
+  RIE (sanei_genesys_write_register
+       (dev, REG0D, REG0D_CLRLNCNT | REG0D_CLRMCNT));
+
+  /* enable scan and motor */
+  RIE (sanei_genesys_read_register (dev, REG01, &val));
+  val |= REG01_SCAN;
+  RIE (sanei_genesys_write_register (dev, REG01, val));
+
+  if (start_motor)
+    {
+      RIE (sanei_genesys_write_register (dev, REG0F, 1));
+    }
+  else
+    {
+      RIE (sanei_genesys_write_register (dev, REG0F, 0));
+    }
+
+  DBGCOMPLETED;
+  return status;
+}
+
+
+/* Send the stop scan command */
+static SANE_Status
+gl843_end_scan (Genesys_Device * dev, Genesys_Register_Set * reg,
+		SANE_Bool check_stop)
+{
+  SANE_Status status = SANE_STATUS_GOOD;
+
+  DBG(DBG_proc, "%s (check_stop = %d)\n", __func__, check_stop);
+  if (reg == NULL)
+    return SANE_STATUS_INVAL;
+
+  /* post scan gpio */
+  RIE(sanei_genesys_write_register(dev,0x7e,0x00));
+
+    // turn off XPA lamp if needed
+    // BUG: the if condition below probably shouldn't be enabled when XPA is off
+    if (reg->state.is_xpa_on || reg->state.is_lamp_on) {
+        gl843_set_xpa_lamp_power(dev, false);
+    }
+
+  if (dev->model->is_sheetfed == SANE_TRUE)
+    {
+      status = SANE_STATUS_GOOD;
+    }
+  else				/* flat bed scanners */
+    {
+      status = gl843_stop_action (dev);
+      if (status != SANE_STATUS_GOOD)
+	{
+	  DBG(DBG_error, "%s: failed to stop: %s\n", __func__, sane_strstatus(status));
+	  return status;
+	}
+    }
+
+  DBGCOMPLETED;
+  return status;
+}
+
+/** @brief park XPA lamp
+ * park the XPA lamp if needed
+ */
+static SANE_Status gl843_park_xpa_lamp (Genesys_Device * dev)
+{
+  Genesys_Register_Set local_reg;
+  SANE_Status status = SANE_STATUS_GOOD;
+  GenesysRegister *r;
+  uint8_t val;
+  int loop = 0;
+
+  DBGSTART;
+
+  /* copy scan settings */
+  local_reg = dev->reg;
+
+  /* set a huge feedl and reverse direction */
+  sanei_genesys_set_triple(&local_reg,REG_FEEDL,0xbdcd);
+
+  /* clear scan and feed count */
+  RIE (sanei_genesys_write_register (dev, REG0D, REG0D_CLRLNCNT | REG0D_CLRMCNT));
+
+  /* set up for reverse and no scan */
+  r = sanei_genesys_get_address (&local_reg, REG02);
+  r->value |= REG02_MTRREV;
+  r = sanei_genesys_get_address (&local_reg, REG01);
+  r->value &= ~REG01_SCAN;
+
+  /* write to scanner and start action */
+  RIE (dev->model->cmd_set->bulk_write_register(dev, local_reg));
+  RIE(gl843_set_xpa_motor_power(dev, true));
+    try {
+        status = gl843_start_action (dev);
+    } catch (...) {
+        DBG(DBG_error, "%s: failed to start motor: %s\n", __func__, sane_strstatus(status));
+        try {
+            gl843_stop_action(dev);
+        } catch (...) {}
+        try {
+            // restore original registers
+            dev->model->cmd_set->bulk_write_register(dev, dev->reg);
+        } catch (...) {}
+        throw;
+    }
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed to start motor: %s\n", __func__, sane_strstatus(status));
+      gl843_stop_action (dev);
+      /* restore original registers */
+      dev->model->cmd_set->bulk_write_register(dev, dev->reg);
+      return status;
+    }
+
+      while (loop < 600)	/* do not wait longer then 60 seconds */
+	{
+	  status = sanei_genesys_get_status (dev, &val);
+	  if (status != SANE_STATUS_GOOD)
+	    {
+	      DBG(DBG_error, "%s: failed to read home sensor: %s\n", __func__,
+		  sane_strstatus(status));
+	      return status;
+	    }
+          if (DBG_LEVEL >= DBG_io2)
+            {
+              sanei_genesys_print_status (val);
+            }
+
+	  if (val & REG41_HOMESNR)	/* home sensor */
+	    {
+	      DBG(DBG_info, "%s: reached home position\n", __func__);
+	      DBG(DBG_proc, "%s: finished\n", __func__);
+
+            gl843_set_xpa_motor_power(dev, false);
+            dev->needs_home_ta = SANE_FALSE;
+
+          return SANE_STATUS_GOOD;
+	    }
+          sanei_genesys_sleep_ms(100);
+	  ++loop;
+	}
+
+  /* we are not parked here.... should we fail ? */
+  DBG(DBG_info, "%s: XPA lamp is not parked\n", __func__);
+  DBGCOMPLETED;
+  return SANE_STATUS_GOOD;
+}
+
+/** @brief Moves the slider to the home (top) position slowly
+ * */
+static SANE_Status
+gl843_slow_back_home (Genesys_Device * dev, SANE_Bool wait_until_home)
+{
+  Genesys_Register_Set local_reg;
+  SANE_Status status = SANE_STATUS_GOOD;
+  GenesysRegister *r;
+  uint8_t val;
+  float resolution;
+  int loop = 0;
+
+  DBG(DBG_proc, "%s (wait_until_home = %d)\n", __func__, wait_until_home);
+
+  if (dev->needs_home_ta) {
+    RIE(gl843_park_xpa_lamp(dev));
+  }
+
+  /* regular slow back home */
+  dev->scanhead_position_in_steps = 0;
+
+  /* first read gives HOME_SENSOR true */
+  status = sanei_genesys_get_status (dev, &val);
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed to read home sensor: %s\n", __func__, sane_strstatus(status));
+      return status;
+    }
+  sanei_genesys_sleep_ms(100);
+
+  /* second is reliable */
+  status = sanei_genesys_get_status (dev, &val);
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed to read home sensor: %s\n", __func__, sane_strstatus(status));
+      return status;
+    }
+  if (DBG_LEVEL >= DBG_io)
+    {
+      sanei_genesys_print_status (val);
+    }
+  if (val & HOMESNR)	/* is sensor at home? */
+    {
+      DBGCOMPLETED;
+      return SANE_STATUS_GOOD;
+    }
+
+  local_reg = dev->reg;
+  resolution=sanei_genesys_get_lowest_ydpi(dev);
+
+    const auto& sensor = sanei_genesys_find_sensor(dev, resolution);
+
+    ScanSession session;
+    session.params.xres = resolution;
+    session.params.yres = resolution;
+    session.params.startx = 100;
+    session.params.starty = 40000;
+    session.params.pixels = 100;
+    session.params.lines = 100;
+    session.params.depth = 8;
+    session.params.channels = 1;
+    session.params.scan_method = dev->settings.scan_method;
+    session.params.scan_mode = ScanColorMode::LINEART;
+    session.params.color_filter = dev->settings.color_filter;
+    session.params.flags =  SCAN_FLAG_DISABLE_SHADING |
+                            SCAN_FLAG_DISABLE_GAMMA |
+                            SCAN_FLAG_DISABLE_BUFFER_FULL_MOVE |
+                            SCAN_FLAG_IGNORE_LINE_DISTANCE;
+    gl843_compute_session(dev, session, sensor);
+
+    status = gl843_init_scan_regs(dev, sensor, &local_reg, session);
+
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed to set up registers: %s\n", __func__, sane_strstatus(status));
+      DBGCOMPLETED;
+      return status;
+    }
+
+  /* clear scan and feed count */
+  RIE (sanei_genesys_write_register (dev, REG0D, REG0D_CLRLNCNT | REG0D_CLRMCNT));
+
+  /* set up for reverse and no scan */
+  r = sanei_genesys_get_address(&local_reg, REG02);
+  r->value |= REG02_MTRREV;
+  r = sanei_genesys_get_address(&local_reg, REG01);
+  r->value &= ~REG01_SCAN;
+
+  RIE (dev->model->cmd_set->bulk_write_register(dev, local_reg));
+
+    try {
+        status = gl843_start_action (dev);
+    } catch (...) {
+        DBG(DBG_error, "%s: failed to start motor: %s\n", __func__, sane_strstatus(status));
+        try {
+            gl843_stop_action(dev);
+        } catch (...) {}
+        try {
+            // restore original registers
+            dev->model->cmd_set->bulk_write_register(dev, dev->reg);
+        } catch (...) {}
+        throw;
+    }
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed to start motor: %s\n", __func__, sane_strstatus(status));
+      gl843_stop_action (dev);
+      /* restore original registers */
+      dev->model->cmd_set->bulk_write_register(dev, dev->reg);
+      return status;
+    }
+
+  if (wait_until_home)
+    {
+
+      while (loop < 300)	/* do not wait longer then 30 seconds */
+	{
+	  status = sanei_genesys_get_status (dev, &val);
+	  if (status != SANE_STATUS_GOOD)
+	    {
+	      DBG(DBG_error, "%s: failed to read home sensor: %s\n", __func__,
+		  sane_strstatus(status));
+	      return status;
+	    }
+          if (DBG_LEVEL >= DBG_io2)
+            {
+              sanei_genesys_print_status (val);
+            }
+
+	  if (val & REG41_HOMESNR)	/* home sensor */
+	    {
+	      DBG(DBG_info, "%s: reached home position\n", __func__);
+	      DBG(DBG_proc, "%s: finished\n", __func__);
+	      return SANE_STATUS_GOOD;
+	    }
+          sanei_genesys_sleep_ms(100);
+	  ++loop;
+	}
+
+      /* when we come here then the scanner needed too much time for this, so we better stop the motor */
+      gl843_stop_action (dev);
+      DBG(DBG_error, "%s: timeout while waiting for scanhead to go home\n", __func__);
+      return SANE_STATUS_IO_ERROR;
+    }
+
+  DBG(DBG_info, "%s: scanhead is still moving\n", __func__);
+  DBGCOMPLETED;
+  return SANE_STATUS_GOOD;
+}
+
+/* Automatically set top-left edge of the scan area by scanning a 200x200 pixels
+   area at 600 dpi from very top of scanner */
+static SANE_Status
+gl843_search_start_position (Genesys_Device * dev)
+{
+  int size;
+  SANE_Status status = SANE_STATUS_GOOD;
+  Genesys_Register_Set local_reg;
+  int steps;
+
+  int pixels = 600;
+  int dpi = 300;
+
+  DBG(DBG_proc, "%s\n", __func__);
+
+  local_reg = dev->reg;
+
+  /* sets for a 200 lines * 600 pixels */
+  /* normal scan with no shading */
+
+    // FIXME: the current approach of doing search only for one resolution does not work on scanners
+    // whith employ different sensors with potentially different settings.
+    auto& sensor = sanei_genesys_find_sensor_for_write(dev, dpi);
+
+    ScanSession session;
+    session.params.xres = dpi;
+    session.params.yres = dpi;
+    session.params.startx = 0;
+    session.params.starty = 0; // we should give a small offset here - ~60 steps
+    session.params.pixels = 600;
+    session.params.lines = dev->model->search_lines;
+    session.params.depth = 8;
+    session.params.channels = 1;
+    session.params.scan_method = dev->settings.scan_method;
+    session.params.scan_mode = ScanColorMode::GRAY;
+    session.params.color_filter = ColorFilter::GREEN;
+    session.params.flags =  SCAN_FLAG_DISABLE_SHADING |
+                            SCAN_FLAG_DISABLE_GAMMA |
+                            SCAN_FLAG_IGNORE_LINE_DISTANCE |
+                            SCAN_FLAG_DISABLE_BUFFER_FULL_MOVE;
+    gl843_compute_session(dev, session, sensor);
+
+    status = gl843_init_scan_regs(dev, sensor, &local_reg, session);
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed to bulk setup registers: %s\n", __func__, sane_strstatus(status));
+      return status;
+    }
+
+  /* send to scanner */
+  status = dev->model->cmd_set->bulk_write_register(dev, local_reg);
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed to bulk write registers: %s\n", __func__, sane_strstatus(status));
+      return status;
+    }
+
+  size = dev->read_bytes_left;
+
+  std::vector<uint8_t> data(size);
+
+  status = gl843_begin_scan(dev, sensor, &local_reg, SANE_TRUE);
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed to begin scan: %s\n", __func__, sane_strstatus(status));
+      return status;
+    }
+
+  /* waits for valid data */
+  do
+    sanei_genesys_test_buffer_empty (dev, &steps);
+  while (steps);
+
+  /* now we're on target, we can read data */
+  status = sanei_genesys_read_data_from_scanner(dev, data.data(), size);
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed to read data: %s\n", __func__, sane_strstatus(status));
+      return status;
+    }
+  RIE(gl843_stop_action_no_move(dev, &local_reg));
+
+  if (DBG_LEVEL >= DBG_data)
+    sanei_genesys_write_pnm_file("gl843_search_position.pnm", data.data(), 8, 1, pixels,
+                                 dev->model->search_lines);
+
+  status = gl843_end_scan(dev, &local_reg, SANE_TRUE);
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed to end scan: %s\n", __func__, sane_strstatus(status));
+      return status;
+    }
+
+  /* update regs to copy ASIC internal state */
+  dev->reg = local_reg;
+
+  status =
+    sanei_genesys_search_reference_point (dev, sensor, data.data(), 0, dpi, pixels,
+					  dev->model->search_lines);
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed to set search reference point: %s\n", __func__,
+          sane_strstatus(status));
+      return status;
+    }
+
+  return SANE_STATUS_GOOD;
+}
+
+/*
+ * sets up register for coarse gain calibration
+ * todo: check it for scanners using it */
+static SANE_Status
+gl843_init_regs_for_coarse_calibration(Genesys_Device * dev, const Genesys_Sensor& sensor,
+                                       Genesys_Register_Set& regs)
+{
+  SANE_Status status = SANE_STATUS_GOOD;
+  uint8_t channels;
+  uint8_t cksel;
+
+  DBGSTART;
+  cksel = (regs.find_reg(0x18).value & REG18_CKSEL) + 1;	/* clock speed = 1..4 clocks */
+
+  /* set line size */
+  if (dev->settings.scan_mode == ScanColorMode::COLOR_SINGLE_PASS)
+    channels = 3;
+  else
+    channels = 1;
+
+  int flags = SCAN_FLAG_DISABLE_SHADING |
+              SCAN_FLAG_DISABLE_GAMMA |
+              SCAN_FLAG_SINGLE_LINE |
+              SCAN_FLAG_IGNORE_LINE_DISTANCE;
+
+    if (dev->settings.scan_method == ScanMethod::TRANSPARENCY) {
+        flags |= SCAN_FLAG_USE_XPA;
+    }
+
+    ScanSession session;
+    session.params.xres = dev->settings.xres;
+    session.params.yres = dev->settings.yres;
+    session.params.startx = 0;
+    session.params.starty = 0;
+    session.params.pixels = sensor.optical_res / cksel; // XXX STEF XXX dpi instead of pixels!
+    session.params.lines = 20;
+    session.params.depth = 16;
+    session.params.channels = channels;
+    session.params.scan_method = dev->settings.scan_method;
+    session.params.scan_mode = dev->settings.scan_mode;
+    session.params.color_filter = dev->settings.color_filter;
+    session.params.flags = flags;
+    gl843_compute_session(dev, session, sensor);
+
+    status = gl843_init_scan_regs(dev, sensor, &regs, session);
+
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed to setup scan: %s\n", __func__, sane_strstatus(status));
+      return status;
+    }
+  sanei_genesys_set_motor_power(regs, false);
+
+  DBG(DBG_info, "%s: optical sensor res: %d dpi, actual res: %d\n", __func__,
+      sensor.optical_res / cksel, dev->settings.xres);
+
+  status = dev->model->cmd_set->bulk_write_register(dev, regs);
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed to bulk write registers: %s\n", __func__, sane_strstatus(status));
+      return status;
+    }
+
+  DBGCOMPLETED;
+  return SANE_STATUS_GOOD;
+}
+
+/** @brief moves the slider to steps at motor base dpi
+ * @param dev device to work on
+ * @param steps number of steps to move
+ * */
+static SANE_Status
+gl843_feed (Genesys_Device * dev, unsigned int steps)
+{
+  Genesys_Register_Set local_reg;
+  SANE_Status status = SANE_STATUS_GOOD;
+  GenesysRegister *r;
+  float resolution;
+  uint8_t val;
+
+  DBGSTART;
+
+  /* prepare local registers */
+  local_reg = dev->reg;
+
+  resolution=sanei_genesys_get_lowest_ydpi(dev);
+
+    const auto& sensor = sanei_genesys_find_sensor(dev, resolution);
+
+    ScanSession session;
+    session.params.xres = resolution;
+    session.params.yres = resolution;
+    session.params.startx = 0;
+    session.params.starty = steps;
+    session.params.pixels = 100;
+    session.params.lines = 3;
+    session.params.depth = 8;
+    session.params.channels = 3;
+    session.params.scan_method = dev->settings.scan_method;
+    session.params.scan_mode = ScanColorMode::COLOR_SINGLE_PASS;
+    session.params.color_filter = ColorFilter::RED;
+    session.params.flags =  SCAN_FLAG_DISABLE_SHADING |
+                            SCAN_FLAG_DISABLE_GAMMA |
+                            SCAN_FLAG_FEEDING |
+                            SCAN_FLAG_IGNORE_LINE_DISTANCE;
+    gl843_compute_session(dev, session, sensor);
+
+    status = gl843_init_scan_regs(dev, sensor, &local_reg, session);
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed to set up registers: %s\n", __func__, sane_strstatus(status));
+      DBGCOMPLETED;
+      return status;
+    }
+
+  /* clear scan and feed count */
+  RIE (sanei_genesys_write_register (dev, REG0D, REG0D_CLRLNCNT));
+  RIE (sanei_genesys_write_register (dev, REG0D, REG0D_CLRMCNT));
+
+  /* set up for no scan */
+  r = sanei_genesys_get_address(&local_reg, REG01);
+  r->value &= ~REG01_SCAN;
+
+  /* send registers */
+  RIE (dev->model->cmd_set->bulk_write_register(dev, local_reg));
+
+    try {
+        status = gl843_start_action (dev);
+    } catch (...) {
+        DBG(DBG_error, "%s: failed to start motor: %s\n", __func__, sane_strstatus(status));
+        try {
+            gl843_stop_action(dev);
+        } catch (...) {}
+        try {
+            // restore original registers
+            dev->model->cmd_set->bulk_write_register(dev, dev->reg);
+        } catch (...) {}
+        throw;
+    }
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed to start motor: %s\n", __func__, sane_strstatus(status));
+      gl843_stop_action (dev);
+
+      /* restore original registers */
+      dev->model->cmd_set->bulk_write_register(dev, dev->reg);
+      return status;
+    }
+
+  /* wait until feed count reaches the required value, but do not
+   * exceed 30s */
+  do
+    {
+          status = sanei_genesys_get_status (dev, &val);
+    }
+  while (status == SANE_STATUS_GOOD && !(val & FEEDFSH));
+
+  // looks like the scanner locks up if we scan immediately after feeding
+  sanei_genesys_sleep_ms(100);
+
+  DBGCOMPLETED;
+  return SANE_STATUS_GOOD;
+}
+
+static SANE_Status gl843_move_to_ta (Genesys_Device * dev);
+
+/* init registers for shading calibration */
+/* shading calibration is done at dpihw */
+static SANE_Status
+gl843_init_regs_for_shading(Genesys_Device * dev, const Genesys_Sensor& sensor,
+                            Genesys_Register_Set& regs)
+{
+  SANE_Status status = SANE_STATUS_GOOD;
+  int move, resolution, dpihw, factor;
+  uint16_t strpixel;
+
+  DBGSTART;
+
+  /* initial calibration reg values */
+  regs = dev->reg;
+
+  dev->calib_channels = 3;
+  if (dev->settings.scan_method == ScanMethod::TRANSPARENCY)
+    dev->calib_lines = dev->model->shading_ta_lines;
+  else
+    dev->calib_lines = dev->model->shading_lines;
+  dpihw = sanei_genesys_compute_dpihw_calibration(dev, sensor, dev->settings.xres);
+  factor=sensor.optical_res/dpihw;
+  resolution=dpihw;
+
+  const auto& calib_sensor = sanei_genesys_find_sensor(dev, resolution,
+                                                       dev->settings.scan_method);
+
+    if (dev->settings.scan_method == ScanMethod::TRANSPARENCY &&
+        dev->model->model_id == MODEL_CANON_CANOSCAN_8600F &&
+        dev->settings.xres == 4800)
+    {
+        float offset = SANE_UNFIX(dev->model->x_offset_ta);
+        offset /= calib_sensor.get_ccd_size_divisor_for_dpi(resolution);
+        offset = (offset * calib_sensor.optical_res) / MM_PER_INCH;
+
+        unsigned size = SANE_UNFIX(dev->model->x_size_ta);
+        size /= calib_sensor.get_ccd_size_divisor_for_dpi(resolution);
+        size = (size * calib_sensor.optical_res) / MM_PER_INCH;
+
+        dev->calib_pixels_offset = offset;
+        dev->calib_pixels = size;
+    }
+    else
+    {
+        dev->calib_pixels_offset = 0;
+        dev->calib_pixels = calib_sensor.sensor_pixels / factor;
+    }
+
+  dev->calib_resolution = resolution;
+
+  int flags = SCAN_FLAG_DISABLE_SHADING |
+              SCAN_FLAG_DISABLE_GAMMA |
+              SCAN_FLAG_DISABLE_BUFFER_FULL_MOVE |
+              SCAN_FLAG_IGNORE_LINE_DISTANCE;
+
+  if (dev->settings.scan_method == ScanMethod::TRANSPARENCY)
+  {
+        // note: move_to_ta() function has already been called and the sensor is at the
+        // transparency adapter
+    move = 0; // already at dev->model->y_offset_calib_ta implicitly
+    flags |= SCAN_FLAG_USE_XPA;
+  }
+  else
+    move = SANE_UNFIX(dev->model->y_offset_calib);
+
+  move = (move * resolution) / MM_PER_INCH;
+
+    ScanSession session;
+    session.params.xres = resolution;
+    session.params.yres = resolution;
+    session.params.startx = dev->calib_pixels_offset;
+    session.params.starty = move;
+    session.params.pixels = dev->calib_pixels;
+    session.params.lines = dev->calib_lines;
+    session.params.depth = 16;
+    session.params.channels = dev->calib_channels;
+    session.params.scan_method = dev->settings.scan_method;
+    session.params.scan_mode = dev->settings.scan_mode;
+    session.params.color_filter = dev->settings.color_filter;
+    session.params.flags = flags;
+    gl843_compute_session(dev, session, calib_sensor);
+
+    status = gl843_init_scan_regs(dev, calib_sensor, &regs, session);
+
+  // the pixel number may be updated to conform to scanner constraints
+  dev->calib_pixels = dev->current_setup.pixels;
+
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed to setup scan: %s\n", __func__, sane_strstatus(status));
+      return status;
+    }
+
+  dev->calib_total_bytes_to_read = dev->read_bytes_left;
+
+  dev->scanhead_position_in_steps += dev->calib_lines + move;
+  sanei_genesys_get_double(&regs,REG_STRPIXEL,&strpixel);
+  DBG(DBG_info, "%s: STRPIXEL=%d\n", __func__, strpixel);
+
+  status = dev->model->cmd_set->bulk_write_register(dev, regs);
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed to bulk write registers: %s\n", __func__, sane_strstatus(status));
+      return status;
+    }
+
+  DBGCOMPLETED;
+  return SANE_STATUS_GOOD;
+}
+
+/** @brief set up registers for the actual scan
+ */
+static SANE_Status
+gl843_init_regs_for_scan (Genesys_Device * dev, const Genesys_Sensor& sensor)
+{
+  int channels;
+  int flags;
+  int depth;
+  float move;
+  int move_dpi;
+  float start;
+
+  SANE_Status status = SANE_STATUS_GOOD;
+
+    DBG(DBG_info, "%s ", __func__);
+    debug_dump(DBG_info, dev->settings);
+
+  /* channels */
+  if (dev->settings.scan_mode == ScanColorMode::COLOR_SINGLE_PASS)
+    channels = 3;
+  else
+    channels = 1;
+
+  /* depth */
+  depth = dev->settings.depth;
+  if (dev->settings.scan_mode == ScanColorMode::LINEART)
+    depth = 1;
+
+  move_dpi = dev->motor.base_ydpi;
+
+  flags = 0;
+  if (dev->settings.scan_method == ScanMethod::TRANSPARENCY)
+  {
+        // note: move_to_ta() function has already been called and the sensor is at the
+        // transparency adapter
+    move = SANE_UNFIX(dev->model->y_offset_ta) - SANE_UNFIX(dev->model->y_offset_calib_ta);
+    flags |= SCAN_FLAG_USE_XPA;
+  }
+  else
+    move = SANE_UNFIX(dev->model->y_offset);
+
+  move += dev->settings.tl_y;
+  move = (move * move_dpi) / MM_PER_INCH;
+  DBG(DBG_info, "%s: move=%f steps\n", __func__, move);
+
+  /* start */
+  if(dev->settings.scan_method==ScanMethod::TRANSPARENCY)
+      start = SANE_UNFIX (dev->model->x_offset_ta);
+  else
+      start = SANE_UNFIX (dev->model->x_offset);
+
+  start /= sensor.get_ccd_size_divisor_for_dpi(dev->settings.xres);
+  start += dev->settings.tl_x;
+  start = (start * sensor.optical_res) / MM_PER_INCH;
+
+  /* enable emulated lineart from gray data */
+  if(dev->settings.scan_mode == ScanColorMode::LINEART
+     && dev->settings.dynamic_lineart)
+    {
+      flags |= SCAN_FLAG_DYNAMIC_LINEART;
+    }
+
+    ScanSession session;
+    session.params.xres = dev->settings.xres;
+    session.params.yres = dev->settings.yres;
+    session.params.startx = start;
+    session.params.starty = move;
+    session.params.pixels = dev->settings.pixels;
+    session.params.lines = dev->settings.lines;
+    session.params.depth = depth;
+    session.params.channels = channels;
+    session.params.scan_method = dev->settings.scan_method;
+    session.params.scan_mode = dev->settings.scan_mode;
+    session.params.color_filter = dev->settings.color_filter;
+    session.params.flags = flags;
+    gl843_compute_session(dev, session, sensor);
+
+    status = gl843_init_scan_regs(dev, sensor, &dev->reg, session);
+
+  if (status != SANE_STATUS_GOOD)
+    return status;
+
+  DBGCOMPLETED;
+  return SANE_STATUS_GOOD;
+}
+
+/**
+ * This function sends gamma tables to ASIC
+ */
+static SANE_Status
+gl843_send_gamma_table(Genesys_Device* dev, const Genesys_Sensor& sensor)
+{
+  int size;
+  SANE_Status status = SANE_STATUS_GOOD;
+  int i;
+
+  DBGSTART;
+
+  size = 256;
+
+  /* allocate temporary gamma tables: 16 bits words, 3 channels */
+  std::vector<uint8_t> gamma(size * 2 * 3);
+
+    std::vector<uint16_t> rgamma = get_gamma_table(dev, sensor, GENESYS_RED);
+    std::vector<uint16_t> ggamma = get_gamma_table(dev, sensor, GENESYS_GREEN);
+    std::vector<uint16_t> bgamma = get_gamma_table(dev, sensor, GENESYS_BLUE);
+
+    // copy sensor specific's gamma tables
+    for (i = 0; i < size; i++) {
+        gamma[i * 2 + size * 0 + 0] = rgamma[i] & 0xff;
+        gamma[i * 2 + size * 0 + 1] = (rgamma[i] >> 8) & 0xff;
+        gamma[i * 2 + size * 2 + 0] = ggamma[i] & 0xff;
+        gamma[i * 2 + size * 2 + 1] = (ggamma[i] >> 8) & 0xff;
+        gamma[i * 2 + size * 4 + 0] = bgamma[i] & 0xff;
+        gamma[i * 2 + size * 4 + 1] = (bgamma[i] >> 8) & 0xff;
+    }
+
+  /* send address */
+  status = gl843_set_buffer_address (dev, 0x0000);
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed to set buffer address: %s\n", __func__, sane_strstatus(status));
+      return status;
+    }
+
+  /* send data */
+  status = sanei_genesys_bulk_write_data(dev, 0x28, gamma.data(), size * 2 * 3);
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed to send gamma table: %s\n", __func__, sane_strstatus(status));
+      return status;
+    }
+
+  DBG(DBG_proc, "%s: completed\n", __func__);
+  return SANE_STATUS_GOOD;
+}
+
+/* this function does the led calibration by scanning one line of the calibration
+   area below scanner's top on white strip.
+
+-needs working coarse/gain
+*/
+static SANE_Status
+gl843_led_calibration (Genesys_Device * dev, Genesys_Sensor& sensor, Genesys_Register_Set& regs)
+{
+  int num_pixels;
+  int total_size;
+  int used_res;
+  int i, j;
+  SANE_Status status = SANE_STATUS_GOOD;
+  int val;
+  int channels, depth;
+  int avg[3], avga, avge;
+  int turn;
+  uint16_t expr, expg, expb;
+
+  SANE_Bool acceptable = SANE_FALSE;
+
+  DBG(DBG_proc, "%s\n", __func__);
+
+  /* offset calibration is always done in color mode */
+  channels = 3;
+  depth = 16;
+  used_res = sensor.optical_res;
+
+  auto& calib_sensor = sanei_genesys_find_sensor_for_write(dev, used_res,
+                                                           dev->settings.scan_method);
+  num_pixels =
+    (calib_sensor.sensor_pixels * used_res) / calib_sensor.optical_res;
+
+  /* initial calibration reg values */
+  regs = dev->reg;
+
+    ScanSession session;
+    session.params.xres = used_res;
+    session.params.yres = dev->motor.base_ydpi;
+    session.params.startx = 0;
+    session.params.starty = 0;
+    session.params.pixels = num_pixels;
+    session.params.lines = 1;
+    session.params.depth = depth;
+    session.params.channels = channels;
+    session.params.scan_method = dev->settings.scan_method;
+    session.params.scan_mode = ScanColorMode::COLOR_SINGLE_PASS;
+    session.params.color_filter = dev->settings.color_filter;
+    session.params.flags =  SCAN_FLAG_DISABLE_SHADING |
+                            SCAN_FLAG_DISABLE_GAMMA |
+                            SCAN_FLAG_SINGLE_LINE |
+                            SCAN_FLAG_IGNORE_LINE_DISTANCE;
+    gl843_compute_session(dev, session, calib_sensor);
+
+    status = gl843_init_scan_regs(dev, calib_sensor, &regs, session);
+
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed to setup scan: %s\n", __func__, sane_strstatus(status));
+      return status;
+    }
+
+  RIE(dev->model->cmd_set->bulk_write_register(dev, regs));
+
+  total_size = dev->read_bytes_left;
+
+  std::vector<uint8_t> line(total_size);
+
+/*
+   we try to get equal bright leds here:
+
+   loop:
+     average per color
+     adjust exposure times
+ */
+
+  expr = calib_sensor.exposure.red;
+  expg = calib_sensor.exposure.green;
+  expb = calib_sensor.exposure.blue;
+
+  turn = 0;
+
+  do
+    {
+
+      calib_sensor.exposure.red = expr;
+      calib_sensor.exposure.green = expg;
+      calib_sensor.exposure.blue = expb;
+
+      sanei_genesys_set_exposure(regs, calib_sensor.exposure);
+
+      RIE(dev->model->cmd_set->bulk_write_register(dev, regs));
+
+      DBG(DBG_info, "%s: starting first line reading\n", __func__);
+      RIE (gl843_begin_scan(dev, calib_sensor, &regs, SANE_TRUE));
+      RIE (sanei_genesys_read_data_from_scanner(dev, line.data(), total_size));
+      RIE(gl843_stop_action_no_move(dev, &regs));
+
+      if (DBG_LEVEL >= DBG_data)
+	{
+          char fn[30];
+          snprintf(fn, 30, "gl843_led_%02d.pnm", turn);
+          sanei_genesys_write_pnm_file(fn, line.data(), depth, channels, num_pixels, 1);
+	}
+
+      acceptable = SANE_TRUE;
+
+      for (j = 0; j < channels; j++)
+	{
+	  avg[j] = 0;
+	  for (i = 0; i < num_pixels; i++)
+	    {
+	      if (dev->model->is_cis)
+		val =
+		  line[i * 2 + j * 2 * num_pixels + 1] * 256 +
+		  line[i * 2 + j * 2 * num_pixels];
+	      else
+		val =
+		  line[i * 2 * channels + 2 * j + 1] * 256 +
+		  line[i * 2 * channels + 2 * j];
+	      avg[j] += val;
+	    }
+
+	  avg[j] /= num_pixels;
+	}
+
+      DBG(DBG_info, "%s: average: %d,%d,%d\n", __func__, avg[0], avg[1], avg[2]);
+
+      acceptable = SANE_TRUE;
+
+      if (avg[0] < avg[1] * 0.95 || avg[1] < avg[0] * 0.95 ||
+	  avg[0] < avg[2] * 0.95 || avg[2] < avg[0] * 0.95 ||
+	  avg[1] < avg[2] * 0.95 || avg[2] < avg[1] * 0.95)
+	acceptable = SANE_FALSE;
+
+      if (!acceptable)
+	{
+	  avga = (avg[0] + avg[1] + avg[2]) / 3;
+	  expr = (expr * avga) / avg[0];
+	  expg = (expg * avga) / avg[1];
+	  expb = (expb * avga) / avg[2];
+/*
+  keep the resulting exposures below this value.
+  too long exposure drives the ccd into saturation.
+  we may fix this by relying on the fact that
+  we get a striped scan without shading, by means of
+  statistical calculation
+*/
+	  avge = (expr + expg + expb) / 3;
+
+	  /* don't overflow max exposure */
+	  if (avge > 3000)
+	    {
+	      expr = (expr * 2000) / avge;
+	      expg = (expg * 2000) / avge;
+	      expb = (expb * 2000) / avge;
+	    }
+	  if (avge < 50)
+	    {
+	      expr = (expr * 50) / avge;
+	      expg = (expg * 50) / avge;
+	      expb = (expb * 50) / avge;
+	    }
+
+	}
+
+      RIE (gl843_stop_action (dev));
+
+      turn++;
+
+    }
+  while (!acceptable && turn < 100);
+
+  DBG(DBG_info, "%s: acceptable exposure: %d,%d,%d\n", __func__, expr, expg, expb);
+
+  sensor.exposure = calib_sensor.exposure;
+
+  gl843_slow_back_home (dev, SANE_TRUE);
+
+  DBG(DBG_proc, "%s: completed\n", __func__);
+  return status;
+}
+
+
+
+/**
+ * average dark pixels of a 8 bits scan of a given channel
+ */
+static int
+dark_average_channel (uint8_t * data, unsigned int pixels, unsigned int lines,
+	      unsigned int channels, unsigned int black, int channel)
+{
+  unsigned int i, j, k, count;
+  unsigned int avg[3];
+  uint8_t val;
+
+  /* computes average values on black margin */
+  for (k = 0; k < channels; k++)
+    {
+      avg[k] = 0;
+      count = 0;
+      // FIXME: start with the second line because the black pixels often have noise on the first
+      // line; the cause is probably incorrectly cleaned up previous scan
+      for (i = 1; i < lines; i++)
+	{
+	  for (j = 0; j < black; j++)
+	    {
+	      val = data[i * channels * pixels + j*channels + k];
+	      avg[k] += val;
+	      count++;
+	    }
+	}
+      if (count)
+	avg[k] /= count;
+      DBG(DBG_info, "%s: avg[%d] = %d\n", __func__, k, avg[k]);
+    }
+  DBG(DBG_info, "%s: average = %d\n", __func__, avg[channel]);
+  return avg[channel];
+}
+
+/** @brief calibrate AFE offset
+ * Iterate doing scans at target dpi until AFE offset if correct. One
+ * color line is scanned at a time. Scanning head doesn't move.
+ * @param dev device to calibrate
+ */
+static SANE_Status
+gl843_offset_calibration(Genesys_Device * dev, const Genesys_Sensor& sensor,
+                         Genesys_Register_Set& regs)
+{
+  SANE_Status status = SANE_STATUS_GOOD;
+  unsigned int channels, bpp;
+  int pass, total_size, i, resolution, lines;
+  int topavg[3], bottomavg[3], avg[3];
+  int top[3], bottom[3], black_pixels, pixels, factor, dpihw;
+
+  DBGSTART;
+
+  /* offset calibration is always done in color mode */
+  channels = 3;
+  lines = 8;
+  bpp = 8;
+
+  /* compute divider factor to compute final pixels number */
+  dpihw = sanei_genesys_compute_dpihw_calibration(dev, sensor, dev->settings.xres);
+  factor = sensor.optical_res / dpihw;
+  resolution = dpihw;
+
+  const auto& calib_sensor = sanei_genesys_find_sensor(dev, resolution,
+                                                       dev->settings.scan_method);
+
+  int target_pixels = calib_sensor.sensor_pixels / factor;
+  int start_pixel = 0;
+  black_pixels = calib_sensor.black_pixels / factor;
+
+    if (dev->settings.scan_method == ScanMethod::TRANSPARENCY &&
+        dev->model->model_id == MODEL_CANON_CANOSCAN_8600F &&
+        dev->settings.xres == 4800)
+    {
+        start_pixel = SANE_UNFIX(dev->model->x_offset_ta);
+        start_pixel /= calib_sensor.get_ccd_size_divisor_for_dpi(resolution);
+        start_pixel = (start_pixel * calib_sensor.optical_res) / MM_PER_INCH;
+
+        target_pixels = SANE_UNFIX(dev->model->x_size_ta);
+        target_pixels /= calib_sensor.get_ccd_size_divisor_for_dpi(resolution);
+        target_pixels = (target_pixels * calib_sensor.optical_res) / MM_PER_INCH;
+    }
+
+  int flags = SCAN_FLAG_DISABLE_SHADING |
+              SCAN_FLAG_DISABLE_GAMMA |
+              SCAN_FLAG_SINGLE_LINE |
+              SCAN_FLAG_IGNORE_LINE_DISTANCE;
+
+  if (dev->settings.scan_method == ScanMethod::TRANSPARENCY)
+  {
+    flags |= SCAN_FLAG_USE_XPA;
+  }
+
+    ScanSession session;
+    session.params.xres = resolution;
+    session.params.yres = resolution;
+    session.params.startx = start_pixel;
+    session.params.starty = 0;
+    session.params.pixels = target_pixels;
+    session.params.lines = lines;
+    session.params.depth = bpp;
+    session.params.channels = channels;
+    session.params.scan_method = dev->settings.scan_method;
+    session.params.scan_mode = ScanColorMode::COLOR_SINGLE_PASS;
+    session.params.color_filter = ColorFilter::RED;
+    session.params.flags = flags;
+    gl843_compute_session(dev, session, calib_sensor);
+    pixels = session.output_pixels;
+
+    DBG(DBG_io, "%s: dpihw       =%d\n", __func__, dpihw);
+    DBG(DBG_io, "%s: factor      =%d\n", __func__, factor);
+    DBG(DBG_io, "%s: resolution  =%d\n", __func__, resolution);
+    DBG(DBG_io, "%s: pixels      =%d\n", __func__, pixels);
+    DBG(DBG_io, "%s: black_pixels=%d\n", __func__, black_pixels);
+    status = gl843_init_scan_regs(dev, calib_sensor, &regs, session);
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed to setup scan: %s\n", __func__, sane_strstatus(status));
+      return status;
+    }
+  sanei_genesys_set_motor_power(regs, false);
+
+  /* allocate memory for scans */
+  total_size = dev->read_bytes_left;
+
+  std::vector<uint8_t> first_line(total_size);
+  std::vector<uint8_t> second_line(total_size);
+
+  /* init gain and offset */
+  for (i = 0; i < 3; i++)
+    {
+      bottom[i] = 10;
+      dev->frontend.set_offset(i, bottom[i]);
+      dev->frontend.set_gain(i, 0);
+    }
+  RIE(gl843_set_fe(dev, calib_sensor, AFE_SET));
+
+  /* scan with obttom AFE settings */
+  RIE(dev->model->cmd_set->bulk_write_register(dev, regs));
+  DBG(DBG_info, "%s: starting first line reading\n", __func__);
+  RIE(gl843_begin_scan(dev, calib_sensor, &regs, SANE_TRUE));
+  RIE(sanei_genesys_read_data_from_scanner(dev, first_line.data(), total_size));
+  RIE(gl843_stop_action_no_move(dev, &regs));
+
+  if (DBG_LEVEL >= DBG_data)
+    {
+      char fn[40];
+      snprintf(fn, 40, "gl843_bottom_offset_%03d_%03d_%03d.pnm",
+               bottom[0], bottom[1], bottom[2]);
+      sanei_genesys_write_pnm_file(fn, first_line.data(), bpp, channels, pixels, lines);
+    }
+
+  for (i = 0; i < 3; i++)
+    {
+      bottomavg[i] = dark_average_channel(first_line.data(), pixels, lines, channels, black_pixels, i);
+      DBG(DBG_io2, "%s: bottom avg %d=%d\n", __func__, i, bottomavg[i]);
+    }
+
+  /* now top value */
+  for (i = 0; i < 3; i++)
+    {
+      top[i] = 255;
+      dev->frontend.set_offset(i, top[i]);
+    }
+  RIE(gl843_set_fe(dev, calib_sensor, AFE_SET));
+
+  /* scan with top AFE values */
+  RIE(dev->model->cmd_set->bulk_write_register(dev, regs));
+  DBG(DBG_info, "%s: starting second line reading\n", __func__);
+  RIE(gl843_begin_scan(dev, calib_sensor, &regs, SANE_TRUE));
+  RIE(sanei_genesys_read_data_from_scanner(dev, second_line.data(), total_size));
+  RIE(gl843_stop_action_no_move(dev, &regs));
+
+  for (i = 0; i < 3; i++)
+    {
+      topavg[i] = dark_average_channel(second_line.data(), pixels, lines, channels, black_pixels, i);
+      DBG(DBG_io2, "%s: top avg %d=%d\n", __func__, i, topavg[i]);
+    }
+
+  pass = 0;
+
+  std::vector<uint8_t> debug_image;
+  size_t debug_image_lines = 0;
+  std::string debug_image_info;
+
+  /* loop until acceptable level */
+  while ((pass < 32)
+	 && ((top[0] - bottom[0] > 1)
+	     || (top[1] - bottom[1] > 1) || (top[2] - bottom[2] > 1)))
+    {
+      pass++;
+
+      /* settings for new scan */
+      for (i = 0; i < 3; i++)
+	{
+	  if (top[i] - bottom[i] > 1)
+	    {
+              dev->frontend.set_offset(i, (top[i] + bottom[i]) / 2);
+	    }
+	}
+      RIE(gl843_set_fe(dev, calib_sensor, AFE_SET));
+
+      /* scan with no move */
+      RIE(dev->model->cmd_set->bulk_write_register(dev, regs));
+      DBG(DBG_info, "%s: starting second line reading\n", __func__);
+      RIE(gl843_begin_scan(dev, calib_sensor, &regs, SANE_TRUE));
+      RIE(sanei_genesys_read_data_from_scanner(dev, second_line.data(), total_size));
+      RIE(gl843_stop_action_no_move(dev, &regs));
+
+      if (DBG_LEVEL >= DBG_data)
+	{
+          char title[100];
+          snprintf(title, 100, "lines: %d pixels_per_line: %d offsets[0..2]: %d %d %d\n",
+                   lines, pixels,
+                   dev->frontend.get_offset(0),
+                   dev->frontend.get_offset(1),
+                   dev->frontend.get_offset(2));
+          debug_image_info += title;
+          std::copy(second_line.begin(), second_line.end(), std::back_inserter(debug_image));
+          debug_image_lines += lines;
+	}
+
+      for (i = 0; i < 3; i++)
+	{
+          avg[i] = dark_average_channel(second_line.data(), pixels, lines, channels, black_pixels, i);
+          DBG(DBG_info, "%s: avg[%d]=%d offset=%d\n", __func__, i, avg[i],
+              dev->frontend.get_offset(i));
+	}
+
+      /* compute new boundaries */
+      for (i = 0; i < 3; i++)
+	{
+	  if (topavg[i] >= avg[i])
+	    {
+	      topavg[i] = avg[i];
+              top[i] = dev->frontend.get_offset(i);
+	    }
+	  else
+	    {
+	      bottomavg[i] = avg[i];
+              bottom[i] = dev->frontend.get_offset(i);
+	    }
+	}
+    }
+
+  if (DBG_LEVEL >= DBG_data)
+    {
+      sanei_genesys_write_file("gl843_offset_all_desc.txt",
+                               (uint8_t*) debug_image_info.data(), debug_image_info.size());
+      sanei_genesys_write_pnm_file("gl843_offset_all.pnm",
+                                   debug_image.data(), bpp, channels, pixels, debug_image_lines);
+    }
+
+  DBG(DBG_info, "%s: offset=(%d,%d,%d)\n", __func__,
+      dev->frontend.get_offset(0),
+      dev->frontend.get_offset(1),
+      dev->frontend.get_offset(2));
+
+  DBGCOMPLETED;
+  return SANE_STATUS_GOOD;
+}
+
+
+/* alternative coarse gain calibration
+   this on uses the settings from offset_calibration and
+   uses only one scanline
+ */
+/*
+  with offset and coarse calibration we only want to get our input range into
+  a reasonable shape. the fine calibration of the upper and lower bounds will
+  be done with shading.
+ */
+static SANE_Status
+gl843_coarse_gain_calibration(Genesys_Device * dev, const Genesys_Sensor& sensor,
+                              Genesys_Register_Set& regs, int dpi)
+{
+  int pixels, factor, dpihw;
+  int total_size;
+  int i, j, channels;
+  SANE_Status status = SANE_STATUS_GOOD;
+  int max[3];
+  float coeff;
+  int val, lines;
+  int resolution;
+  int bpp;
+
+  DBG(DBG_proc, "%s: dpi = %d\n", __func__, dpi);
+  dpihw=sanei_genesys_compute_dpihw_calibration(dev, sensor, dpi);
+  factor=sensor.optical_res/dpihw;
+
+  /* coarse gain calibration is always done in color mode */
+  channels = 3;
+
+  /* follow CKSEL */
+  if (dev->model->ccd_type == CCD_KVSS080)
+    {
+      if(dev->settings.xres<sensor.optical_res)
+        {
+          coeff=0.9;
+        }
+      else
+        {
+          coeff=1.0;
+        }
+    }
+  else
+    {
+      coeff=1.0;
+    }
+  resolution=dpihw;
+  lines=10;
+  bpp=8;
+  int target_pixels = sensor.sensor_pixels / factor;
+
+  int flags = SCAN_FLAG_DISABLE_SHADING |
+              SCAN_FLAG_DISABLE_GAMMA |
+              SCAN_FLAG_SINGLE_LINE |
+              SCAN_FLAG_IGNORE_LINE_DISTANCE;
+
+  if (dev->settings.scan_method == ScanMethod::TRANSPARENCY)
+  {
+    flags |= SCAN_FLAG_USE_XPA;
+  }
+
+    const auto& calib_sensor = sanei_genesys_find_sensor(dev, resolution,
+                                                         dev->settings.scan_method);
+
+    ScanSession session;
+    session.params.xres = resolution;
+    session.params.yres = resolution;
+    session.params.startx = 0;
+    session.params.starty = 0;
+    session.params.pixels = target_pixels;
+    session.params.lines = lines;
+    session.params.depth = bpp;
+    session.params.channels = channels;
+    session.params.scan_method = dev->settings.scan_method;
+    session.params.scan_mode = ScanColorMode::COLOR_SINGLE_PASS;
+    session.params.color_filter = dev->settings.color_filter;
+    session.params.flags = flags;
+    gl843_compute_session(dev, session, calib_sensor);
+    pixels = session.output_pixels;
+
+    try {
+        status = gl843_init_scan_regs(dev, calib_sensor, &regs, session);
+    } catch (...) {
+        try {
+            sanei_genesys_set_motor_power(regs, false);
+        } catch (...) {}
+        throw;
+    }
+
+    sanei_genesys_set_motor_power(regs, false);
+
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed to setup scan: %s\n", __func__, sane_strstatus(status));
+      return status;
+    }
+
+  RIE(dev->model->cmd_set->bulk_write_register(dev, regs));
+
+  total_size = dev->read_bytes_left;
+
+  std::vector<uint8_t> line(total_size);
+
+  RIE(gl843_set_fe(dev, calib_sensor, AFE_SET));
+  RIE(gl843_begin_scan(dev, calib_sensor, &regs, SANE_TRUE));
+  RIE(sanei_genesys_read_data_from_scanner (dev, line.data(), total_size));
+  RIE(gl843_stop_action_no_move(dev, &regs));
+
+  if (DBG_LEVEL >= DBG_data)
+    sanei_genesys_write_pnm_file("gl843_gain.pnm", line.data(), bpp, channels, pixels, lines);
+
+  /* average value on each channel */
+  for (j = 0; j < channels; j++)
+    {
+      max[j] = 0;
+      // FIXME: start from the second line because the first line often has artifacts. Probably
+      // caused by unclean cleanup of previous scans
+      for (i = pixels/4 + pixels; i < (pixels*3/4) + pixels; i++)
+	{
+          if(bpp==16)
+            {
+	  if (dev->model->is_cis)
+	    val =
+	      line[i * 2 + j * 2 * pixels + 1] * 256 +
+	      line[i * 2 + j * 2 * pixels];
+	  else
+	    val =
+	      line[i * 2 * channels + 2 * j + 1] * 256 +
+	      line[i * 2 * channels + 2 * j];
+            }
+          else
+            {
+	  if (dev->model->is_cis)
+	    val = line[i + j * pixels];
+	  else
+	    val = line[i * channels + j];
+            }
+
+	    max[j] += val;
+	}
+      max[j] = max[j] / (pixels/2);
+
+      /*  the flow of data through the frontend ADC is as follows (see e.g. VM8192 datasheet)
+          input
+          -> apply offset (o = i + 260mV * (DAC[7:0]-127.5)/127.5) ->
+          -> apply gain (o = i * 208/(283-PGA[7:0])
+          -> ADC
+
+          Here we have some input data that was acquired with zero gain (PGA==0).
+          We want to compute gain such that the output would approach full ADC range (controlled by
+          gain_white_ref).
+
+          We want to solve the following for {PGA}:
+
+          {input} * 208 / (283 - 0) = {output}
+          {input} * 208 / (283 - {PGA}) = {target output}
+
+          The solution is the following equation:
+
+          {PGA} = 283 * (1 - {output} / {target output})
+      */
+      float gain = ((float) max[j] / (calib_sensor.gain_white_ref*coeff));
+      int code = 283 * (1 - gain);
+      if (code > 255)
+	code = 255;
+      else if (code < 0)
+	code = 0;
+      dev->frontend.set_gain(j, code);
+
+      DBG(DBG_proc, "%s: channel %d, max=%d, gain = %f, setting:%d\n", __func__, j, max[j], gain,
+          code);
+    }
+
+    if (dev->model->is_cis) {
+        uint8_t gain0 = dev->frontend.get_gain(0);
+        if (gain0 > dev->frontend.get_gain(1)) {
+            gain0 = dev->frontend.get_gain(1);
+        }
+        if (gain0 > dev->frontend.get_gain(2)) {
+            gain0 = dev->frontend.get_gain(2);
+        }
+        dev->frontend.set_gain(0, gain0);
+        dev->frontend.set_gain(1, gain0);
+        dev->frontend.set_gain(2, gain0);
+    }
+
+    if (channels == 1) {
+        dev->frontend.set_gain(0, dev->frontend.get_gain(1));
+        dev->frontend.set_gain(2, dev->frontend.get_gain(1));
+    }
+
+  RIE (gl843_stop_action (dev));
+
+  status=gl843_slow_back_home (dev, SANE_TRUE);
+
+  DBGCOMPLETED;
+  return status;
+}
+
+/*
+ * wait for lamp warmup by scanning the same line until difference
+ * between 2 scans is below a threshold
+ */
+static SANE_Status
+gl843_init_regs_for_warmup (Genesys_Device * dev,
+                            const Genesys_Sensor& sensor,
+			    Genesys_Register_Set * reg,
+			    int *channels, int *total_size)
+{
+  int num_pixels;
+  SANE_Status status = SANE_STATUS_GOOD;
+  int dpihw;
+  int resolution;
+  int factor;
+
+  DBGSTART;
+  if (dev == NULL || reg == NULL || channels == NULL || total_size == NULL)
+    return SANE_STATUS_INVAL;
+
+  /* setup scan */
+  *channels=3;
+  resolution=600;
+  dpihw=sanei_genesys_compute_dpihw_calibration(dev, sensor, resolution);
+  resolution=dpihw;
+
+  const auto& calib_sensor = sanei_genesys_find_sensor(dev, resolution,
+                                                       dev->settings.scan_method);
+  factor = calib_sensor.optical_res/dpihw;
+  num_pixels = calib_sensor.sensor_pixels/(factor*2);
+  *total_size = num_pixels * 3 * 1;
+
+  *reg = dev->reg;
+
+    ScanSession session;
+    session.params.xres = resolution;
+    session.params.yres = resolution;
+    session.params.startx = num_pixels/2;
+    session.params.starty = 0;
+    session.params.pixels = num_pixels;
+    session.params.lines = 1;
+    session.params.depth = 8;
+    session.params.channels = *channels;
+    session.params.scan_method = dev->settings.scan_method;
+    session.params.scan_mode = ScanColorMode::COLOR_SINGLE_PASS;
+    session.params.color_filter = dev->settings.color_filter;
+    session.params.flags =  SCAN_FLAG_DISABLE_SHADING |
+                            SCAN_FLAG_DISABLE_GAMMA |
+                            SCAN_FLAG_SINGLE_LINE |
+                            SCAN_FLAG_IGNORE_LINE_DISTANCE;
+    gl843_compute_session(dev, session, calib_sensor);
+
+    status = gl843_init_scan_regs(dev, calib_sensor, reg, session);
+
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed to setup scan: %s\n", __func__, sane_strstatus(status));
+      return status;
+    }
+
+  sanei_genesys_set_motor_power(*reg, false);
+  RIE(dev->model->cmd_set->bulk_write_register(dev, *reg));
+
+  DBGCOMPLETED;
+  return SANE_STATUS_GOOD;
+}
+
+/**
+ * set up GPIO/GPOE for idle state
+WRITE GPIO[17-21]= GPIO19
+WRITE GPOE[17-21]= GPOE21 GPOE20 GPOE19 GPOE18
+genesys_write_register(0xa8,0x3e)
+GPIO(0xa8)=0x3e
+ */
+static SANE_Status
+gl843_init_gpio (Genesys_Device * dev)
+{
+  SANE_Status status = SANE_STATUS_GOOD;
+  int idx;
+
+  DBGSTART;
+
+  RIE (sanei_genesys_write_register (dev, REG6E, dev->gpo.enable[0]));
+  RIE (sanei_genesys_write_register (dev, REG6F, dev->gpo.enable[1]));
+  RIE (sanei_genesys_write_register (dev, REG6C, dev->gpo.value[0]));
+  RIE (sanei_genesys_write_register (dev, REG6D, dev->gpo.value[1]));
+
+  idx=0;
+  while(dev->model->gpo_type != gpios[idx].gpo_type && gpios[idx].gpo_type!=0)
+    {
+      idx++;
+    }
+  if (gpios[idx].gpo_type!=0)
+    {
+      RIE (sanei_genesys_write_register (dev, REGA6, gpios[idx].ra6));
+      RIE (sanei_genesys_write_register (dev, REGA7, gpios[idx].ra7));
+      RIE (sanei_genesys_write_register (dev, REGA8, gpios[idx].ra8));
+      RIE (sanei_genesys_write_register (dev, REGA9, gpios[idx].ra9));
+    }
+  else
+    {
+      status=SANE_STATUS_INVAL;
+    }
+
+  DBGCOMPLETED;
+  return status;
+}
+
+
+/* *
+ * initialize ASIC from power on condition
+ */
+static SANE_Status
+gl843_boot (Genesys_Device * dev, SANE_Bool cold)
+{
+  SANE_Status status = SANE_STATUS_GOOD;
+  uint8_t val;
+
+  DBGSTART;
+
+  if(cold)
+    {
+      RIE (sanei_genesys_write_register (dev, 0x0e, 0x01));
+      RIE (sanei_genesys_write_register (dev, 0x0e, 0x00));
+    }
+
+  if(dev->usb_mode == 1)
+    {
+      val = 0x14;
+    }
+  else
+    {
+      val = 0x11;
+    }
+  RIE (sanei_genesys_write_0x8c (dev, 0x0f, val));
+
+  /* test CHKVER */
+  RIE (sanei_genesys_read_register (dev, REG40, &val));
+  if (val & REG40_CHKVER)
+    {
+      RIE (sanei_genesys_read_register (dev, 0x00, &val));
+      DBG(DBG_info, "%s: reported version for genesys chip is 0x%02x\n", __func__, val);
+    }
+
+  /* Set default values for registers */
+  gl843_init_registers (dev);
+
+  if (dev->model->model_id == MODEL_CANON_CANOSCAN_8600F)
+    {
+      // turns on vref control for maximum current of the motor driver
+      RIE(sanei_genesys_write_register (dev, REG6B, 0x72));
+    }
+  else
+    {
+      RIE(sanei_genesys_write_register (dev, REG6B, 0x02));
+    }
+
+  /* Write initial registers */
+  RIE (dev->model->cmd_set->bulk_write_register(dev, dev->reg));
+
+  // Enable DRAM by setting a rising edge on bit 3 of reg 0x0b
+  val = dev->reg.find_reg(0x0b).value & REG0B_DRAMSEL;
+  val = (val | REG0B_ENBDRAM);
+  RIE (sanei_genesys_write_register (dev, REG0B, val));
+  dev->reg.find_reg(0x0b).value = val;
+
+  if (dev->model->model_id == MODEL_CANON_CANOSCAN_8600F)
+    {
+      RIE (sanei_genesys_write_0x8c (dev, 0x10, 0xc8));
+    }
+  else
+    {
+      RIE (sanei_genesys_write_0x8c (dev, 0x10, 0xb4));
+    }
+
+  /* CLKSET */
+  int clock_freq = REG0B_48MHZ;
+  if (dev->model->model_id == MODEL_CANON_CANOSCAN_8600F)
+    clock_freq = REG0B_60MHZ;
+
+  val = (dev->reg.find_reg(0x0b).value & ~REG0B_CLKSET) | clock_freq;
+
+  RIE (sanei_genesys_write_register (dev, REG0B, val));
+  dev->reg.find_reg(0x0b).value = val;
+
+  /* prevent further writings by bulk write register */
+  dev->reg.remove_reg(0x0b);
+
+  if (dev->model->model_id != MODEL_CANON_CANOSCAN_8600F)
+    {
+      // set up end access
+      // FIXME: this is overwritten in gl843_init_gpio
+      sanei_genesys_write_register(dev, REGA7, 0x04);
+      sanei_genesys_write_register(dev, REGA9, 0x00);
+    }
+
+  /* set RAM read address */
+  RIE (sanei_genesys_write_register (dev, REG29, 0x00));
+  RIE (sanei_genesys_write_register (dev, REG2A, 0x00));
+  RIE (sanei_genesys_write_register (dev, REG2B, 0x00));
+
+  /* setup gpio */
+  RIE (gl843_init_gpio (dev));
+
+  gl843_feed (dev, 300);
+  sanei_genesys_sleep_ms(100);
+
+  DBGCOMPLETED;
+  return SANE_STATUS_GOOD;
+}
+
+/* *
+ * initialize backend and ASIC : registers, motor tables, and gamma tables
+ * then ensure scanner's head is at home
+ */
+static SANE_Status
+gl843_init (Genesys_Device * dev)
+{
+  SANE_Status status = SANE_STATUS_GOOD;
+
+  DBG_INIT ();
+  DBGSTART;
+
+  status=sanei_genesys_asic_init(dev, 0);
+
+  DBGCOMPLETED;
+  return status;
+}
+
+static SANE_Status
+gl843_update_hardware_sensors (Genesys_Scanner * s)
+{
+  /* do what is needed to get a new set of events, but try to not lose
+     any of them.
+   */
+  SANE_Status status = SANE_STATUS_GOOD;
+  uint8_t val;
+
+  RIE (sanei_genesys_read_register (s->dev, REG6D, &val));
+
+  switch (s->dev->model->gpo_type)
+    {
+        case GPO_KVSS080:
+            s->buttons[BUTTON_SCAN_SW].write((val & 0x04) == 0);
+            break;
+        case GPO_G4050:
+            s->buttons[BUTTON_SCAN_SW].write((val & 0x01) == 0);
+            s->buttons[BUTTON_FILE_SW].write((val & 0x02) == 0);
+            s->buttons[BUTTON_EMAIL_SW].write((val & 0x04) == 0);
+            s->buttons[BUTTON_COPY_SW].write((val & 0x08) == 0);
+            break;
+        case GPO_CS4400F:
+        case GPO_CS8400F:
+        default:
+            break;
+    }
+
+  return status;
+}
+
+/** @brief move sensor to transparency adaptor
+ * Move sensor to the calibration of the transparency adapator (XPA).
+ * @param dev device to use
+ */
+static SANE_Status
+gl843_move_to_ta (Genesys_Device * dev)
+{
+  SANE_Status status = SANE_STATUS_GOOD;
+  float resolution;
+  unsigned int feed;
+
+  DBGSTART;
+
+  resolution=sanei_genesys_get_lowest_ydpi(dev);
+  feed = 16*(SANE_UNFIX (dev->model->y_offset_calib_ta) * resolution) / MM_PER_INCH;
+  status = gl843_feed (dev, feed);
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed to move to XPA calibration area\n", __func__);
+      return status;
+    }
+
+  DBGCOMPLETED;
+  return status;
+}
+
+
+/** @brief search for a full width black or white strip.
+ * This function searches for a black or white stripe across the scanning area.
+ * When searching backward, the searched area must completely be of the desired
+ * color since this area will be used for calibration which scans forward.
+ * @param dev scanner device
+ * @param forward SANE_TRUE if searching forward, SANE_FALSE if searching backward
+ * @param black SANE_TRUE if searching for a black strip, SANE_FALSE for a white strip
+ * @return SANE_STATUS_GOOD if a matching strip is found, SANE_STATUS_UNSUPPORTED if not
+ */
+static SANE_Status
+gl843_search_strip (Genesys_Device * dev, const Genesys_Sensor& sensor,
+                    SANE_Bool forward, SANE_Bool black)
+{
+  unsigned int pixels, lines, channels;
+  SANE_Status status = SANE_STATUS_GOOD;
+  Genesys_Register_Set local_reg;
+  size_t size;
+  int steps, depth, dpi;
+  unsigned int pass, count, found, x, y;
+  GenesysRegister *r;
+
+  DBG(DBG_proc, "%s %s %s\n", __func__, black ? "black" : "white", forward ? "forward" : "reverse");
+
+  gl843_set_fe(dev, sensor, AFE_SET);
+  status = gl843_stop_action (dev);
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed to stop: %s\n", __func__, sane_strstatus(status));
+      return status;
+    }
+
+  /* set up for a gray scan at lowest dpi */
+  dpi = sanei_genesys_get_lowest_dpi(dev);
+  channels = 1;
+
+  const auto& calib_sensor = sanei_genesys_find_sensor(dev, dpi, dev->settings.scan_method);
+
+  /* 10 MM */
+  /* lines = (10 * dpi) / MM_PER_INCH; */
+  /* shading calibation is done with dev->motor.base_ydpi */
+  lines = (dev->model->shading_lines * dpi) / dev->motor.base_ydpi;
+  depth = 8;
+  pixels = (calib_sensor.sensor_pixels * dpi) / calib_sensor.optical_res;
+
+  dev->scanhead_position_in_steps = 0;
+
+  local_reg = dev->reg;
+
+    ScanSession session;
+    session.params.xres = dpi;
+    session.params.yres = dpi;
+    session.params.startx = 0;
+    session.params.starty = 0;
+    session.params.pixels = pixels;
+    session.params.lines = lines;
+    session.params.depth = depth;
+    session.params.channels = channels;
+    session.params.scan_method = dev->settings.scan_method;
+    session.params.scan_mode = ScanColorMode::GRAY;
+    session.params.color_filter = ColorFilter::RED;
+    session.params.flags = SCAN_FLAG_DISABLE_SHADING | SCAN_FLAG_DISABLE_SHADING;
+    gl843_compute_session(dev, session, calib_sensor);
+
+    status = gl843_init_scan_regs(dev, calib_sensor, &local_reg, session);
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed to setup for scan: %s\n", __func__, sane_strstatus(status));
+      return status;
+    }
+
+  size = dev->read_bytes_left;
+  std::vector<uint8_t> data(size);
+
+  /* set up for reverse or forward */
+  r = sanei_genesys_get_address(&local_reg, REG02);
+  if (forward)
+    r->value &= ~REG02_MTRREV;
+  else
+    r->value |= REG02_MTRREV;
+
+
+  status = dev->model->cmd_set->bulk_write_register(dev, local_reg);
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed to bulk write registers: %s\n", __func__, sane_strstatus(status));
+      return status;
+    }
+
+  status = gl843_begin_scan(dev, calib_sensor, &local_reg, SANE_TRUE);
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed to begin scan: %s\n", __func__, sane_strstatus(status));
+      return status;
+    }
+
+  /* waits for valid data */
+  do
+    sanei_genesys_test_buffer_empty (dev, &steps);
+  while (steps);
+
+  /* now we're on target, we can read data */
+  status = sanei_genesys_read_data_from_scanner(dev, data.data(), size);
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed to read data: %s\n", __func__, sane_strstatus(status));
+      return status;
+    }
+
+  status = gl843_stop_action (dev);
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: gl843_stop_action failed\n", __func__);
+      return status;
+    }
+
+  pass = 0;
+  if (DBG_LEVEL >= DBG_data)
+    {
+      char fn[40];
+      snprintf(fn, 40, "gl843_search_strip_%s_%s%02d.pnm",
+               black ? "black" : "white", forward ? "fwd" : "bwd", (int)pass);
+      sanei_genesys_write_pnm_file(fn, data.data(), depth, channels, pixels, lines);
+    }
+
+  /* loop until strip is found or maximum pass number done */
+  found = 0;
+  while (pass < 20 && !found)
+    {
+      status =
+        dev->model->cmd_set->bulk_write_register(dev, local_reg);
+      if (status != SANE_STATUS_GOOD)
+	{
+	  DBG(DBG_error, "%s: failed to bulk write registers: %s\n", __func__,
+	      sane_strstatus(status));
+	  return status;
+	}
+
+      /* now start scan */
+      status = gl843_begin_scan(dev, calib_sensor, &local_reg, SANE_TRUE);
+      if (status != SANE_STATUS_GOOD)
+	{
+          DBG(DBG_error, "%s: failed to begin scan: %s\n", __func__, sane_strstatus(status));
+	  return status;
+	}
+
+      /* waits for valid data */
+      do
+	sanei_genesys_test_buffer_empty (dev, &steps);
+      while (steps);
+
+      /* now we're on target, we can read data */
+      status = sanei_genesys_read_data_from_scanner(dev, data.data(), size);
+      if (status != SANE_STATUS_GOOD)
+	{
+          DBG(DBG_error, "%s: failed to read data: %s\n", __func__, sane_strstatus(status));
+	  return status;
+	}
+
+      status = gl843_stop_action (dev);
+      if (status != SANE_STATUS_GOOD)
+	{
+	  DBG(DBG_error, "%s: gl843_stop_action failed\n", __func__);
+	  return status;
+	}
+
+      if (DBG_LEVEL >= DBG_data)
+	{
+          char fn[40];
+          snprintf(fn, 40, "gl843_search_strip_%s_%s%02d.pnm",
+                   black ? "black" : "white", forward ? "fwd" : "bwd", (int)pass);
+          sanei_genesys_write_pnm_file(fn, data.data(), depth, channels, pixels, lines);
+	}
+
+      /* search data to find black strip */
+      /* when searching forward, we only need one line of the searched color since we
+       * will scan forward. But when doing backward search, we need all the area of the
+       * same color */
+      if (forward)
+	{
+	  for (y = 0; y < lines && !found; y++)
+	    {
+	      count = 0;
+	      /* count of white/black pixels depending on the color searched */
+	      for (x = 0; x < pixels; x++)
+		{
+		  /* when searching for black, detect white pixels */
+		  if (black && data[y * pixels + x] > 90)
+		    {
+		      count++;
+		    }
+		  /* when searching for white, detect black pixels */
+		  if (!black && data[y * pixels + x] < 60)
+		    {
+		      count++;
+		    }
+		}
+
+	      /* at end of line, if count >= 3%, line is not fully of the desired color
+	       * so we must go to next line of the buffer */
+	      /* count*100/pixels < 3 */
+	      if ((count * 100) / pixels < 3)
+		{
+		  found = 1;
+		  DBG(DBG_data, "%s: strip found forward during pass %d at line %d\n", __func__,
+		      pass, y);
+		}
+	      else
+		{
+		  DBG(DBG_data, "%s: pixels=%d, count=%d (%d%%)\n", __func__, pixels, count,
+		      (100 * count) / pixels);
+		}
+	    }
+	}
+      else			/* since calibration scans are done forward, we need the whole area
+				   to be of the required color when searching backward */
+	{
+	  count = 0;
+	  for (y = 0; y < lines; y++)
+	    {
+	      /* count of white/black pixels depending on the color searched */
+	      for (x = 0; x < pixels; x++)
+		{
+		  /* when searching for black, detect white pixels */
+		  if (black && data[y * pixels + x] > 90)
+		    {
+		      count++;
+		    }
+		  /* when searching for white, detect black pixels */
+		  if (!black && data[y * pixels + x] < 60)
+		    {
+		      count++;
+		    }
+		}
+	    }
+
+	  /* at end of area, if count >= 3%, area is not fully of the desired color
+	   * so we must go to next buffer */
+	  if ((count * 100) / (pixels * lines) < 3)
+	    {
+	      found = 1;
+	      DBG(DBG_data, "%s: strip found backward during pass %d \n", __func__, pass);
+	    }
+	  else
+	    {
+	      DBG(DBG_data, "%s: pixels=%d, count=%d (%d%%)\n", __func__, pixels, count,
+		  (100 * count) / pixels);
+	    }
+	}
+      pass++;
+    }
+  if (found)
+    {
+      status = SANE_STATUS_GOOD;
+      DBG(DBG_info, "%s: %s strip found\n", __func__, black ? "black" : "white");
+    }
+  else
+    {
+      status = SANE_STATUS_UNSUPPORTED;
+      DBG(DBG_info, "%s: %s strip not found\n", __func__, black ? "black" : "white");
+    }
+
+  DBG(DBG_proc, "%s: completed\n", __func__);
+  return status;
+}
+
+/**
+ * Send shading calibration data. The buffer is considered to always hold values
+ * for all the channels.
+ */
+static SANE_Status
+gl843_send_shading_data (Genesys_Device * dev, const Genesys_Sensor& sensor,
+                         uint8_t * data, int size)
+{
+  SANE_Status status = SANE_STATUS_GOOD;
+  uint32_t final_size, length, i;
+  uint8_t *buffer;
+  int count,offset;
+  unsigned int cksel;
+  GenesysRegister *r;
+  uint16_t dpiset, strpixel, endpixel, startx, factor;
+
+  DBGSTART;
+
+  offset=0;
+  length=size;
+  r = sanei_genesys_get_address(&dev->reg, REG01);
+  if(r->value & REG01_SHDAREA)
+    {
+      /* recompute STRPIXEL used shading calibration so we can
+       * compute offset within data for SHDAREA case */
+      r = sanei_genesys_get_address(&dev->reg, REG18);
+      cksel= (r->value & REG18_CKSEL)+1;
+      sanei_genesys_get_double(&dev->reg,REG_DPISET,&strpixel);
+      sanei_genesys_get_double(&dev->reg,REG_DPISET,&dpiset);
+      factor=sensor.optical_res/sanei_genesys_compute_dpihw(dev, sensor, dpiset);
+
+      /* start coordinate in optical dpi coordinates */
+      startx = (sensor.dummy_pixel / cksel) / factor;
+
+      /* current scan coordinates */
+      sanei_genesys_get_double(&dev->reg,REG_STRPIXEL,&strpixel);
+      sanei_genesys_get_double(&dev->reg,REG_ENDPIXEL,&endpixel);
+
+      if (dev->model->model_id == MODEL_CANON_CANOSCAN_8600F)
+        {
+          int optical_res = sensor.optical_res / dev->current_setup.ccd_size_divisor;
+          int dpiset_real = dpiset / dev->current_setup.ccd_size_divisor;
+          int half_ccd_factor = optical_res /
+              sanei_genesys_compute_dpihw_calibration(dev, sensor, dpiset_real);
+          strpixel /= half_ccd_factor;
+          endpixel /= half_ccd_factor;
+        }
+
+      /* 16 bit words, 2 words per color, 3 color channels */
+      offset=(strpixel-startx)*2*2*3;
+      length=(endpixel-strpixel)*2*2*3;
+      DBG(DBG_info, "%s: STRPIXEL=%d, ENDPIXEL=%d, startx=%d\n", __func__, strpixel, endpixel,
+          startx);
+    }
+
+  /* compute and allocate size for final data */
+  final_size = ((length+251) / 252) * 256;
+  DBG(DBG_io, "%s: final shading size=%04x (length=%d)\n", __func__, final_size, length);
+  std::vector<uint8_t> final_data(final_size, 0);
+
+  /* copy regular shading data to the expected layout */
+  buffer = final_data.data();
+  count = 0;
+
+  /* loop over calibration data */
+  for (i = 0; i < length; i++)
+    {
+      buffer[count] = data[offset+i];
+      count++;
+      if ((count % (256*2)) == (252*2))
+	{
+	  count += 4*2;
+	}
+    }
+
+  /* send data */
+  status = sanei_genesys_set_buffer_address (dev, 0);
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed to set buffer address: %s\n", __func__, sane_strstatus(status));
+      return status;
+    }
+
+  status = dev->model->cmd_set->bulk_write_data (dev, 0x3c, final_data.data(), count);
+  if (status != SANE_STATUS_GOOD)
+    {
+      DBG(DBG_error, "%s: failed to send shading table: %s\n", __func__, sane_strstatus(status));
+    }
+
+  DBGCOMPLETED;
+  return status;
+}
+
+
+/** the gl843 command set */
+static Genesys_Command_Set gl843_cmd_set = {
+  "gl843-generic",		/* the name of this set */
+
+  [](Genesys_Device* dev) -> bool { (void) dev; return true; },
+
+  gl843_init,
+  gl843_init_regs_for_warmup,
+  gl843_init_regs_for_coarse_calibration,
+  gl843_init_regs_for_shading,
+  gl843_init_regs_for_scan,
+
+  gl843_get_filter_bit,
+  gl843_get_lineart_bit,
+  gl843_get_bitset_bit,
+  gl843_get_gain4_bit,
+  gl843_get_fast_feed_bit,
+  gl843_test_buffer_empty_bit,
+  gl843_test_motor_flag_bit,
+
+  gl843_set_fe,
+  gl843_set_powersaving,
+  gl843_save_power,
+
+  gl843_begin_scan,
+  gl843_end_scan,
+
+  gl843_send_gamma_table,
+
+  gl843_search_start_position,
+
+  gl843_offset_calibration,
+  gl843_coarse_gain_calibration,
+  gl843_led_calibration,
+
+  NULL,
+  gl843_slow_back_home,
+  NULL,
+
+  sanei_genesys_bulk_write_register,
+  sanei_genesys_bulk_write_data,
+  sanei_genesys_bulk_read_data,
+
+  gl843_update_hardware_sensors,
+
+  gl843_load_document,
+  gl843_detect_document_end,
+  gl843_eject_document,
+  gl843_search_strip,
+
+  sanei_genesys_is_compatible_calibration,
+  gl843_move_to_ta,
+  gl843_send_shading_data,
+  gl843_calculate_current_setup,
+  gl843_boot
+};
+
+SANE_Status
+sanei_gl843_init_cmd_set (Genesys_Device * dev)
+{
+  dev->model->cmd_set = &gl843_cmd_set;
+  return SANE_STATUS_GOOD;
+}