[linux-dvb] Re: VP-1020

[Jamie Honan <jhonan@optusnet.com.au>]

> Can someone give me a quick rundown on how the digital stream gets from 
> the tuner to the driver in a bt878 based system?

There is a 'second function multimedia device' on the fusion 787a.
You see it if you do an lspci.

On DVB cards this 'device' collects digital data on an
'audio channel', and dma's it to the PCI bus. 
The cards in the bt8xx directory have different but similar systems.

The DST one uses 8 GPIO pins and a clock. You need to get the correct
bt878a doco, as this stuff is quite different to older brooktree
devices.

Conexant Bt878A PCI Video Decoder - User's Manual
        URL: http://www.peritek.com/vgx_878_datasheet.pdf

When looking at any code, you have to get straight in your head
which set of registers are being programmed, function 0 or function 1.

Function 0 is what the bttv driver handles. 

My dst-info.txt describes some of the hardware and the risc
programming from the twinhan driver. The code that was in bt878.c
worked with only a couple of tweaks so I left it alone. The Twinhan
driver used masses more memory.

> I'm taking wild guesses now but my theory is that the bt878 grabs the 
> digital input from the back end of the tuner, massages it into dma 
> frames? and hit's the irq line to tell the driver to transfer the data 
> from the dma buffer to userspace? Or something along those lines..

I'm afraid some deep reading required :)

> Is it possible that somewhere data frames may be getting dropped, which 
> would mean I can't sync the TS properly..
> 
> How would I debug such a problem?

Make sure the cam isn't interfering. Enable some of the irq masks
to do with DMA errors and maybe that will shed light on your theory.

Jamie


-- 
Info:
To unsubscribe send a mail to ecartis@linuxtv.org with "unsubscribe linux-dvb" as subject.