2009-10-04 20:56:12

by Németh Márton

[permalink] [raw]
Subject: [PATCH] pac_common: redesign function for finding Start Of Frame

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;
}
}


2009-10-04 20:57:38

by Németh Márton

[permalink] [raw]
Subject: Re: [PATCH] pac_common: redesign function for finding Start Of Frame

Hi,

I wrote a simple test for pac_find_sof(). I implemented a user-space test
which takes the implementation from the source file and calls it directly.
You can find the source code of the test attached.

The test results for the pac_find_sof() implementation in the Linux kernel
2.6.32-rc1 is the following:

Test case 1: exact match
PDEBUG: SOF found, bytes to analyze: 5. Frame starts at byte #5
PASSED

Test case 2: offset 1
PDEBUG: SOF found, bytes to analyze: 6. Frame starts at byte #6
PASSED

Test case 3: offset 1, first byte may be misleading
FAILED

Test case 4: offset 2, first two bytes may be misleading
PDEBUG: SOF found, bytes to analyze: 7. Frame starts at byte #7
PASSED

Test case 5: offset 3, first three bytes may be misleading
FAILED

Test case 6: offset 4, first four bytes may be misleading
FAILED

Test case 7: pattern starts at end of packet and continues in the next one
PDEBUG: SOF found, bytes to analyze: 1. Frame starts at byte #1
PASSED

Test case 8: splited pattern, with misleading first byte
FAILED

Test case 9: splited pattern, with misleading first three bytes
FAILED

Test case 10: no match, extra byte at offset 1
PASSED

Test case 11: no match, extra byte at offset 2
PASSED

Test case 12: no match, extra byte at offset 3
PASSED

Test case 13: no match, extra byte at offset 4
PASSED

I also executed the test with the patched pac_find_sof() implementation
and that one passes all these test cases.

Regards,

Márton Németh

Németh Márton wrote:
> 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;
> }
> }
>

Attachments:
test_pac_find_sof.c (6.35 kB)

2009-10-05 07:28:46

by Hans de Goede

[permalink] [raw]
Subject: Re: [PATCH] pac_common: redesign function for finding Start Of Frame

Hi,

Good one,

Acked-by: Hans de Goede <[email protected]>

Jean-Francois, can you please add this patch to your tree?

Thanks,

Hans


On 10/04/2009 10:55 PM, Németh Márton wrote:
> 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

2009-10-13 14:44:35

by Subrata Modak

[permalink] [raw]
Subject: Re: [LTP] [PATCH] pac_common: redesign function for finding Start Of Frame

On Sun, 2009-10-04 at 22:56 +0200, Németh Márton wrote:
> Hi,
>
> I wrote a simple test for pac_find_sof(). I implemented a user-space test
> which takes the implementation from the source file and calls it directly.
> You can find the source code of the test attached.

Németh,

Can you please add this test to LTP then ?

Regards--
Subrata

>
> The test results for the pac_find_sof() implementation in the Linux kernel
> 2.6.32-rc1 is the following:
>
> Test case 1: exact match
> PDEBUG: SOF found, bytes to analyze: 5. Frame starts at byte #5
> PASSED
>
> Test case 2: offset 1
> PDEBUG: SOF found, bytes to analyze: 6. Frame starts at byte #6
> PASSED
>
> Test case 3: offset 1, first byte may be misleading
> FAILED
>
> Test case 4: offset 2, first two bytes may be misleading
> PDEBUG: SOF found, bytes to analyze: 7. Frame starts at byte #7
> PASSED
>
> Test case 5: offset 3, first three bytes may be misleading
> FAILED
>
> Test case 6: offset 4, first four bytes may be misleading
> FAILED
>
> Test case 7: pattern starts at end of packet and continues in the next one
> PDEBUG: SOF found, bytes to analyze: 1. Frame starts at byte #1
> PASSED
>
> Test case 8: splited pattern, with misleading first byte
> FAILED
>
> Test case 9: splited pattern, with misleading first three bytes
> FAILED
>
> Test case 10: no match, extra byte at offset 1
> PASSED
>
> Test case 11: no match, extra byte at offset 2
> PASSED
>
> Test case 12: no match, extra byte at offset 3
> PASSED
>
> Test case 13: no match, extra byte at offset 4
> PASSED
>
> I also executed the test with the patched pac_find_sof() implementation
> and that one passes all these test cases.
>
> Regards,
>
> Márton Németh
>
> Németh Márton wrote:
> > 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;
> > }
> > }
> >
>
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