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V4L/DVB (13192): gspca - pac_common: redesign function for finding Start Of Frame

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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.

Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Marton Nemeth <nm127@freemail.hu>
Signed-off-by: Jean-Francois Moine <moinejf@free.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
This commit is contained in:
Marton Nemeth 2009-10-05 05:41:30 -03:00 committed by Mauro Carvalho Chehab
parent 760c466c66
commit e0d49e2d3a
1 changed files with 80 additions and 4 deletions
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84
drivers/media/video/gspca/pac_common.h
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@ -33,6 +33,45 @@
static const unsigned char pac_sof_marker[5] = static const unsigned char pac_sof_marker[5] =
{ 0xff, 0xff, 0x00, 0xff, 0x96 }; { 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, static unsigned char *pac_find_sof(struct gspca_dev *gspca_dev,
unsigned char *m, int len) 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 */ /* Search for the SOF marker (fixed part) in the header */
for (i = 0; i < len; i++) { for (i = 0; i < len; i++) {
if (m[i] == pac_sof_marker[sd->sof_read]) { switch (sd->sof_read) {
sd->sof_read++; case 0:
if (sd->sof_read == sizeof(pac_sof_marker)) { 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, PDEBUG(D_FRAM,
"SOF found, bytes to analyze: %u." "SOF found, bytes to analyze: %u."
" Frame starts at byte #%u", " Frame starts at byte #%u",
len, i + 1); len, i + 1);
sd->sof_read = 0; sd->sof_read = 0;
return m + i + 1; return m + i + 1;
break;
case 0xff:
sd->sof_read = 2;
break;
default:
sd->sof_read = 0;
} }
} else { break;
default:
sd->sof_read = 0; sd->sof_read = 0;
} }
} }