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Message-Id: <1255445014.8438.65.camel@subratamodak.linux.ibm.com>
Date: Tue, 13 Oct 2009 20:13:34 +0530
From: Subrata Modak <subrata@...ux.vnet.ibm.com>
To: Németh Márton <nm127@...email.hu>
Cc: Jean-Francois Moine <moinejf@...e.fr>,
Thomas Kaiser <thomas@...ser-linux.li>,
Kyle Guinn <elyk03@...il.com>,
Theodore Kilgore <kilgota@...urn.edu>,
ltp-list@...ts.sourceforge.net,
LKML <linux-kernel@...r.kernel.org>,
V4L Mailing List <linux-media@...r.kernel.org>
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 <nm127@...email.hu>
> >
> > 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 <nm127@...email.hu>
> > ---
> > --- 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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