[Elphel-support] Status of Theora FPGA encoder

[Andrey Filippov]

Sebastien,

I probably answered those questions on our IRC (
http://irc.elphel.com/irclogs/elphel.2011-05-03.log.html )

On Sat, Apr 30, 2011 at 5:04 PM, Sebastien Bourdeauducq <
sebastien at milkymist.org> wrote:

> Hi,
>
> I am planning to implement network video streaming features into the
> Milkymist One (www.milkymist.org).
>
> For this purpose, your Theora encoder obviously came to mind. But I have
> some concerns about the Verilog code you have published:
> http://elphel.cvs.sourceforge.net/viewvc/elphel/camera333/fpga/x333/
>
> * Is that the right URL where the Theora encoder is?
>

Yes, that is correct url.


> * Where are the test benches? I would guess this code has needed
> extensive simulation to debug it.
>

There are some files *.tf there that I used fro testing in 2005, but I was
making modifications there to fix particular bugs, so most of those were not
posted


> * Why does the code appear to need several clock domains?
>

There are several "natural" domains - sync to sensor pixel clock, memory and
compressor. Each of them I wanted to have separate clock so I could tune to
the maximum performance. xclk (same as in our current 353 cameras is half
system frequency clock that used for slower modules giving more freedom to
increase layers of logic between the registers.

Additionally I tried to use multiple phases of the clock to spread register
transitions in time - in the older 313 camera I had some problems with data
integrity because of the spikes on the ground/power lines caused by massive
simultaneous register transitions. Since then I improved the PCB layout, but
I still try to balance register transitions during clock period.


> * Is there any documentation (design documents, benchmarks, user
> guide ...) about it available somewhere?
>

Unfortunately - not much, as I did not work on this project since 2005. Our
current focus is on preserving as much as possible of the sensor "raw" data,
while Ogg Theora (as other video formats) is intended fro video
distribution. So we mostly use MJPEG format (modified to use JP4 frames
instead of the regular JPEG ones).

Andrey

>
> Thanks,
> Sébastien
>
>
>
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