V4L/DVB (13192): gspca - pac_common: redesign function for finding Start Of Frame (e0d49e2d) · Commits · 戴 / test

drivers/media/video/gspca/pac_common.h

+80 −4

Original line number	Diff line number	Diff line
		@@ -33,6 +33,45 @@
		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(struct gspca_dev gspca_dev,
		unsigned char *m, int len)
		{
		@@ -41,17 +80,54 @@ static unsigned char pac_find_sof(struct gspca_dev gspca_dev,

		/* Search for the SOF marker (fixed part) in the header */
		for (i = 0; i < len; i++) {
		if (m[i] == pac_sof_marker[sd->sof_read]) {
		sd->sof_read++;
		if (sd->sof_read == sizeof(pac_sof_marker)) {
		switch (sd->sof_read) {
		case 0:
		if (m[i] == 0xff)
		sd->sof_read = 1;
		break;
		case 1:
		if (m[i] == 0xff)
		sd->sof_read = 2;
		else
		sd->sof_read = 0;
		break;
		case 2:
		switch (m[i]) {
		case 0x00:
		sd->sof_read = 3;
		break;
		case 0xff:
		/* stay in this state */
		break;
		default:
		sd->sof_read = 0;
		}
		break;
		case 3:
		if (m[i] == 0xff)
		sd->sof_read = 4;
		else
		sd->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);
		sd->sof_read = 0;
		return m + i + 1;
		break;
		case 0xff:
		sd->sof_read = 2;
		break;
		default:
		sd->sof_read = 0;
		}
		} else {
		break;
		default:
		sd->sof_read = 0;
		}
		}

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