Hi, usb iso transfers happen every 1ms (USB1.1) ( or at multiples of 125µs for USB2.0). this timing is fixed and leads to a variable amount of frames available at interrupt. looking at 44100Hz on USB 1.1, we receive/send 44 frames on 9 of 10 USB-interrupts and 45 frames on 1 of 10 USB-interrupts. on first sight 48000Hz seams to lead to a constant 48 frames per interrupt. this does not remain true if the USB-audio device is in sync to an externally connected device (digital in). the current usb-audio mimics constant period size in the USB-interrupt routines by calling snd_period_elapsed() only, if at least full period sizes are transfered on the usb. this good for constant period-size compatibility but leads to sub-optimal latency: i.e. for capture worst case, audio apps start working 1ms later than possible. How can we implement the latency-optimal behaviour with alsa-driver framework? Can we implement something like a snd_1ms_elapsed() routine (called from USB-interrupt), which in turn triggers a waiting app with the available period size (which would be 44 or 45 frames for 44100Hz)? I would like to see this in ALSA / JACK. What do you think?
regards, Karsten __________________________________________________________________ Gesendet von Yahoo! Mail - http://mail.yahoo.de Möchten Sie mit einem Gruß antworten? http://grusskarten.yahoo.de ------------------------------------------------------- This sf.net email is sponsored by: OSDN - Tired of that same old cell phone? Get a new here for FREE! https://www.inphonic.com/r.asp?r=sourceforge1&refcode1=vs3390 _______________________________________________ Alsa-devel mailing list [EMAIL PROTECTED] https://lists.sourceforge.net/lists/listinfo/alsa-devel
