drivers/media/usb/gspca/pac_common.h

   1 /* SPDX-License-Identifier: GPL-2.0-or-later */
   2 /*
   3  * Pixart PAC207BCA / PAC73xx common functions
   4  *
   5  * Copyright (C) 2008 Hans de Goede <j.w.r.degoede@hhs.nl>
   6  * Copyright (C) 2005 Thomas Kaiser thomas@kaiser-linux.li
   7  * Copyleft (C) 2005 Michel Xhaard mxhaard@magic.fr
   8  *
   9  * V4L2 by Jean-Francois Moine <http://moinejf.free.fr>
  10  */
  11
  12 /* We calculate the autogain at the end of the transfer of a frame, at this
  13    moment a frame with the old settings is being captured and transmitted. So
  14    if we adjust the gain or exposure we must ignore at least the next frame for
  15    the new settings to come into effect before doing any other adjustments. */
  16 #define PAC_AUTOGAIN_IGNORE_FRAMES      2
  17
  18 static const unsigned char pac_sof_marker[5] =
  19                 { 0xff, 0xff, 0x00, 0xff, 0x96 };
  20
  21 /*
  22    The following state machine finds the SOF marker sequence
  23    0xff, 0xff, 0x00, 0xff, 0x96 in a byte stream.
  24
  25            +----------+
  26            | 0: START |<---------------\
  27            +----------+<-\             |
  28              |       \---/otherwise    |
  29              v 0xff                    |
  30            +----------+ otherwise      |
  31            |     1    |--------------->*
  32            |          |                ^
  33            +----------+                |
  34              |                         |
  35              v 0xff                    |
  36            +----------+<-\0xff         |
  37         /->|          |--/             |
  38         |  |     2    |--------------->*
  39         |  |          | otherwise      ^
  40         |  +----------+                |
  41         |    |                         |
  42         |    v 0x00                    |
  43         |  +----------+                |
  44         |  |     3    |                |
  45         |  |          |--------------->*
  46         |  +----------+ otherwise      ^
  47         |    |                         |
  48    0xff |    v 0xff                    |
  49         |  +----------+                |
  50         \--|     4    |                |
  51            |          |----------------/
  52            +----------+ otherwise
  53              |
  54              v 0x96
  55            +----------+
  56            |  FOUND   |
  57            +----------+
  58 */
  59
  60 static unsigned char *pac_find_sof(struct gspca_dev *gspca_dev, u8 *sof_read,
  61                                         unsigned char *m, int len)
  62 {
  63         int i;
  64
  65         /* Search for the SOF marker (fixed part) in the header */
  66         for (i = 0; i < len; i++) {
  67                 switch (*sof_read) {
  68                 case 0:
  69                         if (m[i] == 0xff)
  70                                 *sof_read = 1;
  71                         break;
  72                 case 1:
  73                         if (m[i] == 0xff)
  74                                 *sof_read = 2;
  75                         else
  76                                 *sof_read = 0;
  77                         break;
  78                 case 2:
  79                         switch (m[i]) {
  80                         case 0x00:
  81                                 *sof_read = 3;
  82                                 break;
  83                         case 0xff:
  84                                 /* stay in this state */
  85                                 break;
  86                         default:
  87                                 *sof_read = 0;
  88                         }
  89                         break;
  90                 case 3:
  91                         if (m[i] == 0xff)
  92                                 *sof_read = 4;
  93                         else
  94                                 *sof_read = 0;
  95                         break;
  96                 case 4:
  97                         switch (m[i]) {
  98                         case 0x96:
  99                                 /* Pattern found */
 100                                 gspca_dbg(gspca_dev, D_FRAM,
 101                                           "SOF found, bytes to analyze: %u - Frame starts at byte #%u\n",
 102                                           len, i + 1);
 103                                 *sof_read = 0;
 104                                 return m + i + 1;
 105                                 break;
 106                         case 0xff:
 107                                 *sof_read = 2;
 108                                 break;
 109                         default:
 110                                 *sof_read = 0;
 111                         }
 112                         break;
 113                 default:
 114                         *sof_read = 0;
 115                 }
 116         }
 117
 118         return NULL;
 119 }