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. Thanks :) -- 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 GPG Fingerprint - 5596 B766 97C0 0E94 4347 295E E593 DC20 7B3F CE8C _______________________________________________ freebsd-usb@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-usb To unsubscribe, send any mail to "freebsd-usb-unsubscr...@freebsd.org"
