[linux-dvb] [PATCH 6/6] DVB-PinnSat: Misc cleanup and robustness tweaks

Edgar Toernig froese at gmx.de
Tue Jan 10 18:15:41 CET 2006

Manu Abraham wrote:
> Edgar Toernig wrote:
> >All good and fine - but I get no errors with the video fifo,
> >only with the audio fifo.  Afaics, there are only two differences:
> >the video fifo is two times as deep as the audio fifo (but data rates
> >are 4-8 times as high), and the read-only MAX_LAT register which is
> >10us for video and 64us for audio.
> Yeah, that shouldn't happen. Why don't you try grabbing the entire 
> stream as it is from the buffer. This should be almost the same as the 
> transfer from the video fifo. At least that could help in identifying 
> the problem.

The bt878 driver always grabs the entire stream, it's usually between 30
and 40 Mbits/sec = 4-5 Mbyte/s.  A full resolution video (768x576) takes,
depending on color format, between 22 and 44 Mbytes/s.

> >Not the fifo-depth is changed (that's not possible in the bt878), the
> >trigger point at which access to the PCI bus is requested is lowered.
> Changing the trigger point is indirectly having the same effect as that 
> of the buffer size, even though directly it is not handling the buffer size.

Nonsense.  The fifo can hold 140 bytes - that's about 30us for a full
transponder.  If you ask for the PCI bus when the fifo is half full
the PCI arbiter has 15us to grant the bus or the fifo overflows.
If you request the bus when the fifo is only 10% full then the arbiter
has 27us.

Ciao, ET.

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