From: Márton Németh <[email protected]> The original implementation of pac_find_sof() does not always find the Start Of Frame (SOF) marker. Replace it with a state machine based design.
The change was tested with Labtec Webcam 2200. Signed-off-by: Márton Németh <[email protected]> --- --- linux-2.6.32-rc1.orig/drivers/media/video/gspca/pac_common.h 2009-09-10 00:13:59.000000000 +0200 +++ linux-2.6.32-rc1/drivers/media/video/gspca/pac_common.h 2009-10-04 21:49:19.000000000 +0200 @@ -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(struc /* 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; } } -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
