Fixed flipping duplexer initialization

For scanners which potentially have flipping duplexers, only enable
duplexing if there is an ADF present.  This leads to the next problem, that
the flipping duplexers (present only on the HP 8200 series AFAIK) don't
always seem to be properly configured when powered up.  To solve this some
magical values are written to magical memory locations, and some more
magical status is read back, causing an apparent firmware reset which
blocks communication for a short period of time.  See adf_reset() for
details.

backend/avision.c

@@ -3098,10 +3098,63 @@ send_flash_ram_data (Avision_Connection* av_con)
 }
 #endif
 
+
+static SANE_Status
+adf_reset (Avision_Scanner* s)
+{
+  SANE_Status status;
+  Avision_Device* dev = s->hw;
+  struct command_send scmd;
+  struct command_read rcmd;
+  uint8_t payload[4];
+  size_t size;
+  size_t n;
+  int i;
+  DBG (3, "adf_reset\n");
+
+  /* loop twice */
+  for (i=1; i >= 0; i--) {
+    n=i;
+    memset (&scmd, 0, sizeof (scmd));
+    memset (&payload, 0, sizeof (payload));
+    scmd.opc = AVISION_SCSI_SEND;
+    scmd.datatypecode = 0xD0; /* unknown */
+    set_double (scmd.datatypequal, 0);
+    size = 2;
+    set_triple (scmd.transferlen, size);
+    payload[1] = 0x10 * i;  /* write 0x10 the first time, 0x00 the second */
+    status = avision_cmd (&s->av_con, &scmd, sizeof (scmd), payload, size, 0, 0);
+    if (status != SANE_STATUS_GOOD) {
+      DBG (1, "adf_reset: write %d failed (%s)\n", (2-i),
+	 sane_strstatus (status));
+      return (status);
+    }
+    DBG (3, "adf_reset: write %d complete.\n", (2-i));
+
+    memset (&rcmd, 0, sizeof (rcmd));
+    memset (&payload, 0, sizeof (payload));
+    rcmd.opc = AVISION_SCSI_READ;
+    rcmd.datatypecode = 0x69; /* Read NVRAM data */
+    set_double (rcmd.datatypequal, dev->data_dq);
+    size = 4 - i; /* read 3 bytes the first time, 4 the second */
+    set_triple (rcmd.transferlen, size);
+    status = avision_cmd (&s->av_con, &rcmd, sizeof (rcmd), 0, 0, payload, &size);
+    if (status != SANE_STATUS_GOOD || size != (4-n)) {
+      DBG (1, "adf_reset: read %d failed (%s)\n", (2-n),
+	 sane_strstatus (status));
+      return (status);
+    }
+    debug_print_raw (3, "adf_reset: raw data:\n", payload, size);
+  }
+  return SANE_STATUS_GOOD;
+}
+
+
 static SANE_Status
 get_accessories_info (Avision_Scanner* s)
 {
   Avision_Device* dev = s->hw;
+  int try = 3;
   
   /* read stuff */
   struct command_read rcmd;
@@ -3124,6 +3177,9 @@ get_accessories_info (Avision_Scanner* s)
   set_double (rcmd.datatypequal, dev->data_dq);
   set_triple (rcmd.transferlen, size);
  
+  /* after resetting the ADF unit, try reprobing it again */
+  RETRY:
+
   status = avision_cmd (&s->av_con, &rcmd, sizeof (rcmd), 0, 0, result, &size);
   if (status != SANE_STATUS_GOOD || size != sizeof (result)) {
     DBG (1, "get_accessories_info: read failed (%s)\n",
@@ -3144,9 +3200,37 @@ get_accessories_info (Avision_Scanner* s)
 
   if (dev->hw->feature_type2 & AV_ADF_FLIPPING_DUPLEX)
   {
-    dev->inquiry_duplex = 1;
-    dev->inquiry_duplex_interlaced = 0;
-    dev->inquiry_adf_need_mirror_rear = 1;
+    if (result[0] == 1)
+    {
+      dev->inquiry_duplex = 1;
+      dev->inquiry_duplex_interlaced = 0;
+      dev->inquiry_adf_need_mirror_rear = 1;
+    } else if (result[0] == 0 && result[2] != 0) {
+      /* Sometimes the scanner will report that there is no ADF attached, yet
+       * an ADF model number will still be reported.  This happens on the
+       * HP8200 series and possibly others.  In this case we need to reset the
+       * the adf and try reading it again.
+       */
+      DBG (3, "get_accessories_info: Found ADF model number but the ADF-present flag is not set. Trying to recover...\n");
+      status = adf_reset (s);
+      if (status != SANE_STATUS_GOOD) {
+        DBG (3, "get_accessories_info: Failed to reset ADF: %s\n", sane_strstatus (status));
+        return status;
+      }
+      DBG (1, "get_accessories_info: Waiting while ADF firmware resets...\n");
+      sleep(3);
+      status = wait_ready (&s->av_con, 1);
+      if (status != SANE_STATUS_GOOD) {
+        DBG (1, "get_accessories_info: wait_ready() failed: %s\n", sane_strstatus (status));
+        return status;
+      }
+      if (try) {
+        try--;
+        goto RETRY;
+      }
+      DBG (1, "get_accessories_info: Maximum retries attempted, ADF unresponsive.\n");
+      return SANE_STATUS_UNSUPPORTED;
+    }
   }
 
   /* only honor a 1, some scanner without adapter set 0xff */