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 }
131