diff options
| author | Marton Nemeth <nm127@freemail.hu> | 2009-10-05 05:41:30 -0300 |
|---|---|---|
| committer | Mauro Carvalho Chehab <mchehab@redhat.com> | 2009-12-05 18:40:49 -0200 |
| commit | e0d49e2d3ae3cd887b7999c4227c04008d2a02c4 (patch) | |
| tree | cc4cd7e02c1a6fe6a076aaf6398db3ad4e3d185a | |
| parent | 760c466c66db40cde5953e93b94ae20c7610fb20 (diff) | |
V4L/DVB (13192): gspca - pac_common: redesign function for finding Start Of Frame
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>
| -rw-r--r-- | drivers/media/video/gspca/pac_common.h | 84 |
1 files changed, 80 insertions, 4 deletions
diff --git a/drivers/media/video/gspca/pac_common.h b/drivers/media/video/gspca/pac_common.h index 34d4b1494cd5..d3006539fb82 100644 --- a/drivers/media/video/gspca/pac_common.h +++ b/drivers/media/video/gspca/pac_common.h @@ -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; } } |