drivers/media/usb/gspca/pac_common.h

   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
  28 static 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
  70 static 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                                 PDEBUG(D_FRAM,
 111                                         "SOF found, bytes to analyze: %u."
 112                                         " Frame starts at byte #%u",
 113                                         len, i + 1);
 114                                 *sof_read = 0;
 115                                 return m + i + 1;
 116                                 break;
 117                         case 0xff:
 118                                 *sof_read = 2;
 119                                 break;
 120                         default:
 121                                 *sof_read = 0;
 122                         }
 123                         break;
 124                 default:
 125                         *sof_read = 0;
 126                 }
 127         }
 128
 129         return NULL;
 130 }