[linux-dvb] Re: tech questions

[Arpi <arpi@thot.banki.hu>]

Hi,

>  > > The driver send PES of size 2048 bytes or smaller to the firmware. So an
>  > > optimal PES size would be 2048 bytes (including header) or smaller. Of
>  > > course, you would want to start a frame at the beginning of a PES, so
>  > > that the PES before that is usually smaller than 2048 bytes, but
>  > > that's ok. You don't have to use padding. Other PES sizes should be ok
>  > > too, the driver repacks the PES, but it can only make them smaller.
>  > 
>  > Hmm, good to know... I thought the driver puts anything to card's buffer,
>  > and the card handle any size of packets.
>  > 
>  > Changed my PES packetizer to create 2048 byte packets _including_ headers,
>  > and it seems to work better now. At least my favourite stream which hanged
>  > after 12 sec still playing (over 5 mins).

It solved the problem, I could play a whole DVD film without problems.

>  > 
>  > Maybe a memleak or other overflow in the driver's re-packetizer?
> 
> That could be. The re-packer is in dvb_firm.c 
> If you find something please tell us.
Ehh. It's a big hex dump of something, maybe the ARM code... I cannot
even read it :(

> The 2048+header bytes packets also always result in one packet with 2048
> bytes and one very small one with just the header size. 
> Copying just those few bytes is very slow compared to copying 
> 2048 byte blocks and the ARM only has 40 MHz. 
It explains the problem.

> You will also notice that the PES data coming from the board
> has stuffing bytes to 4-byte (DWORD) align the payload to
> the payload in the internal buffers similar as it was done in the
> AVPES format. Copying non-aligned data is slow on ARMs.
So I should align payload (mpeg data only or PTS?) to dword?


A'rpi / Astral & ESP-team

--
mailto:arpi@thot.banki.hu
http://esp-team.scene.hu


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