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. --
