On 28/01/2011, at 18:28, Hans Petter Selasky wrote:
> For this kind of applications ISOCHRONOUS transfers should be used. Then you
> can have a double buffer guard in the range 1-56ms, regardless of the buffer
> size the hardware uses.
That sounds nice :)
I am trying to get it working at the moment, however I'm only finding it
capable of 4 or 8 Mb/sec (512 or 1024 byte EP), although perhaps I don't
understand how to do ISO transfer properly.
BTW do you have a feel for the latency in bulk vs iso? I currently have 5-10
msec of buffering in the hardware which I plan on increasing but I'm not sure
what a reasonable amount would be :)
I put a logic analyser on my board and it shows fairly regular requests from
the hardware (16kbyte bursts every 2msec or so) however I see glitches
occasionally - 5.5ms, 7.5ms.
I am not sure if they are attributable to userland scheduling (in which case
writing a kernel driver should help) or some subtlety in USB itself.
Daniel O'Connor software and network engineer
for Genesis Software - http://www.gsoft.com.au
"The nice thing about standards is that there
are so many of them to choose from."
-- Andrew Tanenbaum
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