[pvrusb2] First take on a chinese oem capture card with FX2 and cx25843

[Mike Isely]

Svenn:

There are a number of different cards I've heard about that pair an FX2 
microcontroller with a cx25843.  Unfortunately none of them are going to 
work with the pvrusb2 driver, since the pvrusb2 driver at its core is 
looking for that mpeg encoder chip.  The mystery chip in that photo is 
interesting - somebody went to the trouble to erase the markings from 
that chip.  However it can't be the mpeg encoder - such a chip will have 
a dram interface and there just aren't enough pins there.

Even if the pvrusb2 driver were to support raw mode (which perhaps 
someday it might), any implementation is probably still going to expect 
to shovel the bits through the encoder.  I've learned a few things about 
how this is probably possible; basically it amounts to putting the 
encoder into a different mode.  It would still be packetizing the data 
but it would be in a form that could then be made available as raw from 
the pvrusb2 driver's API - this is needed because audio still has to be 
interleaved.  Long story, but the takeaway is that the encoder chip is 
still involved.

It might be an interesting exercise to further improve the pvrusb2 
driver to handle cards like you're describing.  The fact is that much of 
the scaffolding is going to be the same - there is after all an FX2 
there and I imagine RPC style communication still going on.  But this is 
a very big deal to implement and I have to think that by now there's 
likely another v4l-dvb driver that already does this.

  -Mike


On Fri, 28 Jan 2011, Svenn Are Bjerkem wrote:

> Hi,
> just out of curiosity (and some need) I bought one of these dvr oem
> usb2 cards which happen to be available for purchase. Normally seems
> to only run under winxp32 and with an application called superdvr.
> I opened the box and took some pictures of the PCB to identify the components.
> 
> http://invalid.ed.ntnu.no/~svenn/html/oem_usb2_capture_card.html
> 
> For a cheap chinese card, I find it funny that they have taken the
> hasle to mount the mini-USB socket while soldering a cable on the back
> side, but that's maybe for production programming. Most of the
> components are traceable, except for one unmarked chip. Since it
> contains the FX2 and cx25843 chip, I have been searching on the net
> for more information on drivers for cards using these chips, and I
> have found that it is mostly TV-tuner cards appearing in the
> discussions. I am trying out several tutorials on programming the FX2
> with the linux driver in order to load a cx25843 firmware, either the
> linux one or the one downloaded by the winxp driver. I have to take
> one step at a time.
> 
> I read on the homepage of the pvrusb2 driver that raw mode is not
> supported yet and this card assumingly does not have an mpeg encoder
> (unless that magic chip is one) and will probably feed some raw data
> on the USB channel. I will have to deal with that if I get that far.
> 
> I post this, probably on the wrong mailinglist, in the hope that some
> other participant ever came across this card and would share any
> experience or pitfalls. I have just recently begun investigating and I
> have really no clue which application should be able to read the data
> that the USB connection provides. I am also in the process on reading
> up on v4l in order to find which direction to proceed. Currently I
> feel I have more knowledge about the chips on the board (I'm a
> hardware engineer) than the driver and application infrastructure.
> 
> Eventually this capture card will be used with a UMPC running Linux to
> monitor moving parts of machinery. (Need to use cheap parts that I can
> afford to lose during development)
> 
> Kind regards,
> 

-- 

Mike Isely
isely @ isely (dot) net
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