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

   1/*
   2 * Pixart PAC207BCA / PAC73xx common functions
   3 *
   4 * Copyright (C) 2008 Hans de Goede <j.w.r.degoede@hhs.nl>
   5 * Copyright (C) 2005 Thomas Kaiser thomas@kaiser-linux.li
   6 * Copyleft (C) 2005 Michel Xhaard mxhaard@magic.fr
   7 *
   8 * V4L2 by Jean-Francois Moine <http://moinejf.free.fr>
   9 *
  10 * This program is free software; you can redistribute it and/or modify
  11 * it under the terms of the GNU General Public License as published by
  12 * the Free Software Foundation; either version 2 of the License, or
  13 * (at your option) any later version.
  14 *
  15 * This program is distributed in the hope that it will be useful,
  16 * but WITHOUT ANY WARRANTY; without even the implied warranty of
  17 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18 * GNU General Public License for more details.
  19 *
  20 */
  21
  22/* We calculate the autogain at the end of the transfer of a frame, at this
  23   moment a frame with the old settings is being captured and transmitted. So
  24   if we adjust the gain or exposure we must ignore atleast the next frame for
  25   the new settings to come into effect before doing any other adjustments. */
  26#define PAC_AUTOGAIN_IGNORE_FRAMES      2
  27
  28static const unsigned char pac_sof_marker[5] =
  29                { 0xff, 0xff, 0x00, 0xff, 0x96 };
  30
  31/*
  32   The following state machine finds the SOF marker sequence
  33   0xff, 0xff, 0x00, 0xff, 0x96 in a byte stream.
  34
  35           +----------+
  36           | 0: START |<---------------\
  37           +----------+<-\             |
  38             |       \---/otherwise    |
  39             v 0xff                    |
  40           +----------+ otherwise      |
  41           |     1    |--------------->*
  42           |          |                ^
  43           +----------+                |
  44             |                         |
  45             v 0xff                    |
  46           +----------+<-\0xff         |
  47        /->|          |--/             |
  48        |  |     2    |--------------->*
  49        |  |          | otherwise      ^
  50        |  +----------+                |
  51        |    |                         |
  52        |    v 0x00                    |
  53        |  +----------+                |
  54        |  |     3    |                |
  55        |  |          |--------------->*
  56        |  +----------+ otherwise      ^
  57        |    |                         |
  58   0xff |    v 0xff                    |
  59        |  +----------+                |
  60        \--|     4    |                |
  61           |          |----------------/
  62           +----------+ otherwise
  63             |
  64             v 0x96
  65           +----------+
  66           |  FOUND   |
  67           +----------+
  68*/
  69
  70static unsigned char *pac_find_sof(struct gspca_dev *gspca_dev, u8 *sof_read,
  71                                        unsigned char *m, int len)
  72{
  73        int i;
  74
  75        /* Search for the SOF marker (fixed part) in the header */
  76        for (i = 0; i < len; i++) {
  77                switch (*sof_read) {
  78                case 0:
  79                        if (m[i] == 0xff)
  80                                *sof_read = 1;
  81                        break;
  82                case 1:
  83                        if (m[i] == 0xff)
  84                                *sof_read = 2;
  85                        else
  86                                *sof_read = 0;
  87                        break;
  88                case 2:
  89                        switch (m[i]) {
  90                        case 0x00:
  91                                *sof_read = 3;
  92                                break;
  93                        case 0xff:
  94                                /* stay in this state */
  95                                break;
  96                        default:
  97                                *sof_read = 0;
  98                        }
  99                        break;
 100                case 3:
 101                        if (m[i] == 0xff)
 102                                *sof_read = 4;
 103                        else
 104                                *sof_read = 0;
 105                        break;
 106                case 4:
 107                        switch (m[i]) {
 108                        case 0x96:
 109                                /* Pattern found */
 110                                gspca_dbg(gspca_dev, D_FRAM,
 111                                          "SOF found, bytes to analyze: %u - Frame starts at byte #%u\n",
 112                                          len, i + 1);
 113                                *sof_read = 0;
 114                                return m + i + 1;
 115                                break;
 116                        case 0xff:
 117                                *sof_read = 2;
 118                                break;
 119                        default:
 120                                *sof_read = 0;
 121                        }
 122                        break;
 123                default:
 124                        *sof_read = 0;
 125                }
 126        }
 127
 128        return NULL;
 129}
 130