Takashi Iwai wrote: > Clemens Ladisch wrote: >> Takashi Iwai wrote: >>> Raymond Yau wrote: >>>> usb-audio seem update when each URB send/receive (in 1ms intervals) >> >> The default is to use larger intervals. >> >>> The usb-audio driver behaved in a BATCH way in the very early version, >>> but it was improved. >> >> The delay reporting is more precise, but the DMA position still jumps >> for each URB. >> >>> So we can get rid of the flag from this driver now. >> >> How well does timer-scheduling work with large URBs? > > I thought PCM runtime delay should give the accurate sample position, > irrespective to URB size? The position of the sample that is currently being played is accurate (rounded to a USB frame). The DMA position, however, changes only in URB-sized increments. (And that is accurate too, because it describes exactly how the data is copied out of the buffer.) > It should suffice for PA to control via timer scheduling. Large jumps in the DMA position mean that there is a large part of the buffer which cannot be safely changed by PA. If this is why PA wants to disable tsched, then the BATCH flag should stay. Regards, Clemens
