Justin Schoeman wrote:
> The Zoran should be easy? Although I seem to rmember it only being
> capable of compressed capture.
>
> Anyway, I can't guarantee this, but my latest measurements show that it
> should be possible to record at full rate and full size from a Bt8x8
> based card. The problem is that you will probably start getting line
> drops. I think full rate NTSC was around 18MB/s. DMA'ing this to
> system memory is no great problem. HOWEVER: When you start to write to
> HDD at the same time, you push up your PCI bus requirements to
> 2*18=36MB's which is still well within spec, but due to arbitration
> latency of the PCI bus, you could have problems...
>
> So, you will just have to try and see! Make sure your harddrives can
> sustain > 25MB/s (a little overhead for seeks, etc.), install the rawio
> patches for the kernel, write a capture driver that can use rawio to
> capture to a raw partition on the HDD without too much kernel overhead,
> get a motherboard with really low latency PCI arbitration, and hope...
On a practical note, I think you're already in trouble here. The best
modern IDE disks can only do about 16-20 MB/s *sustained writes*. At the
hub, I've seen a 43GB SCSI disk do 22MB/s, and tailing off after that. A
10,000rpm 9GB scsi disk was performing similarly I seem to recall. If
you need to sustain 25 or more, you may be able to do this with a
stripeing raid array of 2 or more disks, either scsi, or perhaps one of
the IDE raid controllers. I don't know if the rawio stuff will work on a
raid device tho.
> Sorry, in the end I haven't really answered your question. In theory it
> is definitely possible, but I have a horrible suspision that the
> arbitration latency on the PCI bus is going to keep theory from
> becomming practice...
Stephen.
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