1 /* SPDX-License-Identifier: GPL-2.0-or-later */
2 /*
3 * Pixart PAC207BCA / PAC73xx common functions
4 *
5 * Copyright (C) 2008 Hans de Goede <j.w.r.degoede@hhs.nl>
6 * Copyright (C) 2005 Thomas Kaiser thomas@kaiser-linux.li
7 * Copyleft (C) 2005 Michel Xhaard mxhaard@magic.fr
8 *
9 * V4L2 by Jean-Francois Moine <http://moinejf.free.fr>
10 */
11
12 /* We calculate the autogain at the end of the transfer of a frame, at this
13 moment a frame with the old settings is being captured and transmitted. So
14 if we adjust the gain or exposure we must ignore at least the next frame for
15 the new settings to come into effect before doing any other adjustments. */
16 #define PAC_AUTOGAIN_IGNORE_FRAMES 2
17
18 static const unsigned char pac_sof_marker[5] =
19 { 0xff, 0xff, 0x00, 0xff, 0x96 };
20
21 /*
22 The following state machine finds the SOF marker sequence
23 0xff, 0xff, 0x00, 0xff, 0x96 in a byte stream.
24
25 +----------+
26 | 0: START |<---------------\
27 +----------+<-\ |
28 | \---/otherwise |
29 v 0xff |
30 +----------+ otherwise |
31 | 1 |--------------->*
32 | | ^
33 +----------+ |
34 | |
35 v 0xff |
36 +----------+<-\0xff |
37 /->| |--/ |
38 | | 2 |--------------->*
39 | | | otherwise ^
40 | +----------+ |
41 | | |
42 | v 0x00 |
43 | +----------+ |
44 | | 3 | |
45 | | |--------------->*
46 | +----------+ otherwise ^
47 | | |
48 0xff | v 0xff |
49 | +----------+ |
50 \--| 4 | |
51 | |----------------/
52 +----------+ otherwise
53 |
54 v 0x96
55 +----------+
56 | FOUND |
57 +----------+
58 */
59
60 static unsigned char *pac_find_sof(struct gspca_dev *gspca_dev, u8 *sof_read,
61 unsigned char *m, int len)
62 {
63 int i;
64
65 /* Search for the SOF marker (fixed part) in the header */
66 for (i = 0; i < len; i++) {
67 switch (*sof_read) {
68 case 0:
69 if (m[i] == 0xff)
70 *sof_read = 1;
71 break;
72 case 1:
73 if (m[i] == 0xff)
74 *sof_read = 2;
75 else
76 *sof_read = 0;
77 break;
78 case 2:
79 switch (m[i]) {
80 case 0x00:
81 *sof_read = 3;
82 break;
83 case 0xff:
84 /* stay in this state */
85 break;
86 default:
87 *sof_read = 0;
88 }
89 break;
90 case 3:
91 if (m[i] == 0xff)
92 *sof_read = 4;
93 else
94 *sof_read = 0;
95 break;
96 case 4:
97 switch (m[i]) {
98 case 0x96:
99 /* Pattern found */
100 gspca_dbg(gspca_dev, D_FRAM,
101 "SOF found, bytes to analyze: %u - Frame starts at byte #%u\n",
102 len, i + 1);
103 *sof_read = 0;
104 return m + i + 1;
105 break;
106 case 0xff:
107 *sof_read = 2;
108 break;
109 default:
110 *sof_read = 0;
111 }
112 break;
113 default:
114 *sof_read = 0;
115 }
116 }
117
118 return NULL;
119 }