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 
32 static 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 
74 static unsigned char *pac_find_sof(struct gspca_dev *gspca_dev, 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