RE: Isochronous transmission via OHCI

[Gord P. <Gor...@sm...>]

Yes, that's more likely the culprit than the gap count.

I always tend to attempt the most difficult solution first. ;)

	Gord

> -----Original Message-----
> From: Mark Knecht [mailto:mk...@co...]
> Sent: Wednesday, February 21, 2001 2:40 PM
> To: Ken Offer; Gord Peters
> Cc: Chris Norris; Patrice NEZOU; lin...@li...
> Subject: RE: Isochronous transmission via OHCI
>
>
> Kenneth,
>    What packet size are you transferring when you get 4.1MB/second? 512
> bytes per chance?
>
>    (4.1MB/S) / (8000 cycles/S) = 512 Bytes / Cycle
>
>    It just seemed too accurate for me to pass up asking...
>
>    Just checking that it isn't the amount of data you want to send that's
> limiting how much bandwidth you see yourself using...
>
> Mark
>
> -----Original Message-----
> From: Ken Offer [mailto:ko...@ar...]
> Sent: Wednesday, February 21, 2001 11:09 AM
> To: Gord Peters
> Cc: Chris Norris; Patrice NEZOU; lin...@li...
> Subject: Re: Isochronous transmission via OHCI
>
>
> Gord Peters wrote:
>
> > Of course, video1394 will likely be better for slower computers since it
> > directly maps a chunk of memory from the appliction into the kernel
> > (avoiding memory copies between the kernel and the application) and uses
> > that for it's isochronous data (application feeds iso data into the
> mmap()ed
> > memory and driver reads data from this memory).  Whereas
> libraw1394 copies
> > data on a per packet basis (incurring performance hits in both memory
> copies
> > and extra function calls to send data on a packet by packet basis).
>
> That was my thinking as well.  The DMA attribute is particularly
> attractive for high-data-rate applications.  We're trying to drink from
> a fire-hose (or is that a fire-wire-fire-hose?) ;)
>
> Currently I'm getting a lowly transfer rate of 4.1 MBytes/sec using my
> hacked-up telemetry driver (clone o' video1394).  I'm guessing its
> because I need to nuke some synchronization bit somewhere or convince
> the driver to take up more bandwidth on the bus.
>
> In the routine initialize_dma_it_prg, I found the following line:
>
> 		it_prg[i].data[0] =
> 			(DMA_SPEED_100 << 16)
> 			| (/* tag */ 1 << 14)
> 			| (d->channel << 8)
> 			| (TCODE_ISO_DATA << 4);
>
> I changed the DMA_SPEED_100 to DMA_SPEED_400, but I didn't see any
> change in performance.  I also tried commenting out the following line:
>
> 		if (i==0) it_prg[i].data[0] |= sync_tag;
>
> But that stopped data transmission altogether. I gather I need to do
> more groking... :(
>
> --
> ______________________________________________________________
> Kenneth Ray Offer, II
> Sr. Systems Analyst
> Applied Research Laboratories/SDD
> University of Texas at Austin
> Office (512) 835-3859   FAX (512) 835-3259
>
> Any opinions expressed above are mine and not necessarily
> those of my employer.
>
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