Re: VDR recording glitches

["Ralph Metzler <" <rjkm@netcologne.de>]

Michael Holzt writes:
 > On Wed, Sep 20, 2000 at 02:06:08PM +0200, Carsten Koch wrote:
 > > So, I'd say we're seeing a driver bug (or at least a
 > > driver weakness) here.
 > 
 > I still recommend increasing the buffer size as suggested by Klaus. Fixed
 > the problem 100% for me (even without DMA).

There are still many explanations for this behavior.

- a driver weakness, i.e. it blocks other (IDE) IRQs for too long 

  In the new version the conversion routines maybe should go into a
  bottom half or tasklet. But they were not in the old version where 
  the problem already was present.
  Before there only was a write to a ring buffer inside the IRQ
  which should be fast enough.

  The MMU of the SAA7146 might be used to make a very fast ringbuffer
  which would reduce IRQ times to almost nothing.
  But this will have to wait until after the API change.

- other IRQs block the DVB IRQ which causes dropped AV_PES packets 
  
  This does not seem to be the case for you (Michael) since you have
  no problems without DMA but with bigger buffers)  but it might be
  for others.
  Here setting the unmaskirq feature of hdparm (hdparm -u ...) might
  help if no DMA is available.


- disk caching 

  The disk might be fast anough but data is first written to the
  buffer memory. When the cache is full it suddenly has to write very
  much data and might not be able to free the MPEG buffer quickly enough.
  Does VDR support uncached writing?
   

Ralph