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

Manu Abraham abraham.manu at gmail.com
Wed Jan 11 13:36:34 CET 2006


Edgar Toernig wrote:

>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.
>
>  
>

Heh. The driver does indeed !

>>>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.
>
>  
>
[..]

Manu




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