Messages in this thread Patch in this message | | | From | Kirill Smelkov <> | Subject | [PATCH 5/5] staging/easycap: Fix bytesperline calculation | Date | Mon, 13 Jun 2011 16:18:32 +0400 |
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As described above fillin_formats()
""" /* * THE 16-BIT easycap_format.mask HAS MEANING: * (least significant) BIT 0: 0 => PAL, 25 FPS; 1 => NTSC, 30 FPS * BITS 2-4: RESERVED FOR DIFFERENTIATING STANDARDS * BITS 5-7: NUMBER OF BYTES PER PIXEL * BIT 8: 0 => NATIVE BYTE ORDER; 1 => SWAPPED * BITS 9-10: RESERVED FOR OTHER BYTE PERMUTATIONS * BIT 11: 0 => UNDECIMATED; 1 => DECIMATED * BIT 12: 0 => OFFER FRAMES; 1 => OFFER FIELDS * BIT 13: 0 => FULL FRAMERATE; 1 => REDUCED * (most significant) BITS 14-15: RESERVED FOR OTHER FIELD/FRAME OPTIONS * IT FOLLOWS THAT: * bytesperpixel IS ((0x00E0 & easycap_format.mask) >> 5) * byteswaporder IS true IF (0 != (0x0100 & easycap_format.mask)) * * decimatepixel IS true IF (0 != (0x0800 & easycap_format.mask)) * * offerfields IS true IF (0 != (0x1000 & easycap_format.mask)) */ """
bytes-per-pixel is stored in bits 5-7 of calculated mask.
But when calculating bytes-per-line we were extracting wrong value instead of bytes-per-pixel, which was usually 2 times bigger -- e.g. for PAL YUV 422 I was getting ((mask3 & 0x00F0) >> 4) = 4 bytes instead of 2.
The error here is that even in comments there is a line saying
* bytesperpixel IS ((0x00E0 & easycap_format.mask) >> 5)
but we were using ((0x00F0 & easycap_format.mask) >> 4)
With 2 times bigger bytesperpixel and automatically bytesperline, the video was shown halfheight'ed, which is understandable if we look at video-memory layout:
<------- bytesperline --------> <- real bpl ->
x0----------y0 x1-----------y1 x2----------y2 x3-----------y3
xn----------yn xn-----------yn <garbage>
for each line, we should display width pixels, then move to next line with bytesperline, and oops, if bytesperline = 2*real-bytesperlin, we'll skip one line and move to next-next line, and so only half lines will be shown.
Initially I've debugged the problem with my video application[1], but I've checked that after this patch both rawv (mine app) and tvtime work correctly.
[1] http://repo.or.cz/w/rawv.git
P.S. why at all we use those mask/shifts? Why not use bitfields?
Cc: Tomas Winkler <tomas.winkler@intel.com> Cc: Mike Thomas <rmthomas@sciolus.org> Signed-off-by: Kirill Smelkov <kirr@mns.spb.ru> --- drivers/staging/easycap/easycap_settings.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/drivers/staging/easycap/easycap_settings.c b/drivers/staging/easycap/easycap_settings.c index 898559d..70f59b1 100644 --- a/drivers/staging/easycap/easycap_settings.c +++ b/drivers/staging/easycap/easycap_settings.c @@ -567,7 +567,7 @@ int fillin_formats(void) default: return -3; } - bytesperline = width * ((mask3 & 0x00F0) >> 4); + bytesperline = width * ((mask3 & 0x00E0) >> 5); sizeimage = bytesperline * height; for (m = 0; m < INTERLACE_MANY; m++) { -- 1.7.6.rc1
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