linux-vybrid_public/drivers/media/video/gspca/pac_common.h

/*
 * Pixart PAC207BCA / PAC73xx common functions
 *
 * Copyright (C) 2008 Hans de Goede <j.w.r.degoede@hhs.nl>
 * Copyright (C) 2005 Thomas Kaiser thomas@kaiser-linux.li
 * Copyleft (C) 2005 Michel Xhaard mxhaard@magic.fr
 *
 * V4L2 by Jean-Francois Moine <http://moinejf.free.fr>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 */

/* We calculate the autogain at the end of the transfer of a frame, at this
   moment a frame with the old settings is being transmitted, and a frame is
   being captured with the old settings. So if we adjust the autogain we must
   ignore atleast the 2 next frames for the new settings to come into effect
   before doing any other adjustments */
#define PAC_AUTOGAIN_IGNORE_FRAMES	3

static const unsigned char pac_sof_marker[5] =
		{ 0xff, 0xff, 0x00, 0xff, 0x96 };

/*
   The following state machine finds the SOF marker sequence
   0xff, 0xff, 0x00, 0xff, 0x96 in a byte stream.

	   +----------+
	   | 0: START |<---------------\
	   +----------+<-\             |
	     |       \---/otherwise    |
	     v 0xff                    |
	   +----------+ otherwise      |
	   |     1    |--------------->*
	   |          |                ^
	   +----------+                |
	     |                         |
	     v 0xff                    |
	   +----------+<-\0xff         |
	/->|          |--/             |
	|  |     2    |--------------->*
	|  |          | otherwise      ^
	|  +----------+                |
	|    |                         |
	|    v 0x00                    |
	|  +----------+                |
	|  |     3    |                |
	|  |          |--------------->*
	|  +----------+ otherwise      ^
	|    |                         |
   0xff |    v 0xff                    |
	|  +----------+                |
	\--|     4    |                |
	   |          |----------------/
	   +----------+ otherwise
	     |
	     v 0x96
	   +----------+
	   |  FOUND   |
	   +----------+
*/

static unsigned char *pac_find_sof(u8 *sof_read,
					unsigned char *m, int len)
{
	int i;

	/* Search for the SOF marker (fixed part) in the header */
	for (i = 0; i < len; i++) {
		switch (*sof_read) {
		case 0:
			if (m[i] == 0xff)
				*sof_read = 1;
			break;
		case 1:
			if (m[i] == 0xff)
				*sof_read = 2;
			else
				*sof_read = 0;
			break;
		case 2:
			switch (m[i]) {
			case 0x00:
				*sof_read = 3;
				break;
			case 0xff:
				/* stay in this state */
				break;
			default:
				*sof_read = 0;
			}
			break;
		case 3:
			if (m[i] == 0xff)
				*sof_read = 4;
			else
				*sof_read = 0;
			break;
		case 4:
			switch (m[i]) {
			case 0x96:
				/* Pattern found */
				PDEBUG(D_FRAM,
					"SOF found, bytes to analyze: %u."
					" Frame starts at byte #%u",
					len, i + 1);
				*sof_read = 0;
				return m + i + 1;
				break;
			case 0xff:
				*sof_read = 2;
				break;
			default:
				*sof_read = 0;
			}
			break;
		default:
			*sof_read = 0;
		}
	}

	return NULL;
}