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 * You should have received a copy of the GNU General Public License
  21 * along with this program; if not, write to the Free Software
  22 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  23 *
  24 */
  25
  26/* We calculate the autogain at the end of the transfer of a frame, at this
  27   moment a frame with the old settings is being captured and transmitted. So
  28   if we adjust the gain or exposure we must ignore atleast the next frame for
  29   the new settings to come into effect before doing any other adjustments. */
  30#define PAC_AUTOGAIN_IGNORE_FRAMES      2
  31
  32static const unsigned char pac_sof_marker[5] =
  33                { 0xff, 0xff, 0x00, 0xff, 0x96 };
  34
  35/*
  36   The following state machine finds the SOF marker sequence
  37   0xff, 0xff, 0x00, 0xff, 0x96 in a byte stream.
  38
  39           +----------+
  40           | 0: START |<---------------\
  41           +----------+<-\             |
  42             |       \---/otherwise    |
  43             v 0xff                    |
  44           +----------+ otherwise      |
  45           |     1    |--------------->*
  46           |          |                ^
  47           +----------+                |
  48             |                         |
  49             v 0xff                    |
  50           +----------+<-\0xff         |
  51        /->|          |--/             |
  52        |  |     2    |--------------->*
  53        |  |          | otherwise      ^
  54        |  +----------+                |
  55        |    |                         |
  56        |    v 0x00                    |
  57        |  +----------+                |
  58        |  |     3    |                |
  59        |  |          |--------------->*
  60        |  +----------+ otherwise      ^
  61        |    |                         |
  62   0xff |    v 0xff                    |
  63        |  +----------+                |
  64        \--|     4    |                |
  65           |          |----------------/
  66           +----------+ otherwise
  67             |
  68             v 0x96
  69           +----------+
  70           |  FOUND   |
  71           +----------+
  72*/
  73
  74static unsigned char *pac_find_sof(u8 *sof_read,
  75                                        unsigned char *m, int len)
  76{
  77        int i;
  78
  79        /* Search for the SOF marker (fixed part) in the header */
  80        for (i = 0; i < len; i++) {
  81                switch (*sof_read) {
  82                case 0:
  83                        if (m[i] == 0xff)
  84                                *sof_read = 1;
  85                        break;
  86                case 1:
  87                        if (m[i] == 0xff)
  88                                *sof_read = 2;
  89                        else
  90                                *sof_read = 0;
  91                        break;
  92                case 2:
  93                        switch (m[i]) {
  94                        case 0x00:
  95                                *sof_read = 3;
  96                                break;
  97                        case 0xff:
  98                                /* stay in this state */
  99                                break;
 100                        default:
 101                                *sof_read = 0;
 102                        }
 103                        break;
 104                case 3:
 105                        if (m[i] == 0xff)
 106                                *sof_read = 4;
 107                        else
 108                                *sof_read = 0;
 109                        break;
 110                case 4:
 111                        switch (m[i]) {
 112                        case 0x96:
 113                                /* Pattern found */
 114                                PDEBUG(D_FRAM,
 115                                        "SOF found, bytes to analyze: %u."
 116                                        " Frame starts at byte #%u",
 117                                        len, i + 1);
 118                                *sof_read = 0;
 119                                return m + i + 1;
 120                                break;
 121                        case 0xff:
 122                                *sof_read = 2;
 123                                break;
 124                        default:
 125                                *sof_read = 0;
 126                        }
 127                        break;
 128                default:
 129                        *sof_read = 0;
 130                }
 131        }
 132
 133        return NULL;
 134}
 135