[linux-dvb] Problem with Avermedia 771 : IRQ lockup

Edgar Toernig froese at gmx.de
Fri Sep 30 01:38:14 CEST 2005

Hamish Moffatt wrote:
> >   http://www.linuxtv.org/pipermail/linux-dvb/2005-September/004481.html
> Doesn't this just ignore the errors? Admittedly that might not be a bad 
> solution (although you will get some corruption when it occurs).

It also adds resyncs to the RISC program so that the DMA-engine
can recover.  And it lowers to fifo-threshold so that the errors
are less often.  But yes, you get some errors in the stream - the
PCI-bridge was to slow to respond to the DMA-request and the data
is lost.

> The thread that the OP mentioned discussed interaction between the BT878
> and sata drivers. For me the problem was much worse when I started
> streaming to SATA disk, but I had seen it on occasion before that.

Right, heavy DMA may delay the bus grant for the BT878 long enough that
its fifo overflows.

> But I do recall that it seemed better in earlier kernels (around 2.6.3?).

I had the same impression.  2.6.8 seems to be better.  But I've looked
left and right and couldn't find a single bit of code in the kernel that
would effect the regression :-(

> Maybe there is longer interrupt latency for some reason in newer kernels.

The problem has nothing to do with interrupt latency.  Its the DMA
arbitration and that seems to be configured by the BIOS.

Ciao, ET.

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