drivers/media/video/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  * 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 transmitted, and a frame is
  28    being captured with the old settings. So if we adjust the autogain we must
  29    ignore atleast the 2 next frames for the new settings to come into effect
  30    before doing any other adjustments */
  31 #define PAC_AUTOGAIN_IGNORE_FRAMES      3
  32
  33 static const unsigned char pac_sof_marker[5] =
  34                 { 0xff, 0xff, 0x00, 0xff, 0x96 };
  35
  36 /*
  37    The following state machine finds the SOF marker sequence
  38    0xff, 0xff, 0x00, 0xff, 0x96 in a byte stream.
  39
  40            +----------+
  41            | 0: START |<---------------\
  42            +----------+<-\             |
  43              |       \---/otherwise    |
  44              v 0xff                    |
  45            +----------+ otherwise      |
  46            |     1    |--------------->*
  47            |          |                ^
  48            +----------+                |
  49              |                         |
  50              v 0xff                    |
  51            +----------+<-\0xff         |
  52         /->|          |--/             |
  53         |  |     2    |--------------->*
  54         |  |          | otherwise      ^
  55         |  +----------+                |
  56         |    |                         |
  57         |    v 0x00                    |
  58         |  +----------+                |
  59         |  |     3    |                |
  60         |  |          |--------------->*
  61         |  +----------+ otherwise      ^
  62         |    |                         |
  63    0xff |    v 0xff                    |
  64         |  +----------+                |
  65         \--|     4    |                |
  66            |          |----------------/
  67            +----------+ otherwise
  68              |
  69              v 0x96
  70            +----------+
  71            |  FOUND   |
  72            +----------+
  73 */
  74
  75 static unsigned char *pac_find_sof(u8 *sof_read,
  76                                         unsigned char *m, int len)
  77 {
  78         int i;
  79
  80         /* Search for the SOF marker (fixed part) in the header */
  81         for (i = 0; i < len; i++) {
  82                 switch (*sof_read) {
  83                 case 0:
  84                         if (m[i] == 0xff)
  85                                 *sof_read = 1;
  86                         break;
  87                 case 1:
  88                         if (m[i] == 0xff)
  89                                 *sof_read = 2;
  90                         else
  91                                 *sof_read = 0;
  92                         break;
  93                 case 2:
  94                         switch (m[i]) {
  95                         case 0x00:
  96                                 *sof_read = 3;
  97                                 break;
  98                         case 0xff:
  99                                 /* stay in this state */
 100                                 break;
 101                         default:
 102                                 *sof_read = 0;
 103                         }
 104                         break;
 105                 case 3:
 106                         if (m[i] == 0xff)
 107                                 *sof_read = 4;
 108                         else
 109                                 *sof_read = 0;
 110                         break;
 111                 case 4:
 112                         switch (m[i]) {
 113                         case 0x96:
 114                                 /* Pattern found */
 115                                 PDEBUG(D_FRAM,
 116                                         "SOF found, bytes to analyze: %u."
 117                                         " Frame starts at byte #%u",
 118                                         len, i + 1);
 119                                 *sof_read = 0;
 120                                 return m + i + 1;
 121                                 break;
 122                         case 0xff:
 123                                 *sof_read = 2;
 124                                 break;
 125                         default:
 126                                 *sof_read = 0;
 127                         }
 128                         break;
 129                 default:
 130                         *sof_read = 0;
 131                 }
 132         }
 133
 134         return NULL;
 135 }