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1/* SPDX-License-Identifier: GPL-2.0-or-later */2/*3 * Pixart PAC207BCA / PAC73xx common functions4 *5 * Copyright (C) 2008 Hans de Goede <j.w.r.degoede@hhs.nl>6 * Copyright (C) 2005 Thomas Kaiser thomas@kaiser-linux.li7 * Copyleft (C) 2005 Michel Xhaard mxhaard@magic.fr8 *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 this13 moment a frame with the old settings is being captured and transmitted. So14 if we adjust the gain or exposure we must ignore at least the next frame for15 the new settings to come into effect before doing any other adjustments. */16#define PAC_AUTOGAIN_IGNORE_FRAMES 217 18static const unsigned char pac_sof_marker[5] =19 { 0xff, 0xff, 0x00, 0xff, 0x96 };20 21/*22 The following state machine finds the SOF marker sequence23 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 +----------+ otherwise53 |54 v 0x9655 +----------+56 | FOUND |57 +----------+58*/59 60static 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 else76 *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 else94 *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}120