LXR linux/drivers/media/usb/gspca/pac

   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
  18static 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
  60static 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}
 120