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Do you require the sound card give you accurate playback position ?

No. Just accurate playback (or capture). But reliably, on any system, without hardware-specific tweaks, 'out-of-the-box'. Ideally with the potential for reasonable latency if the user requests that. And not necessarily only on the 'latest' Alsa versions.

at 48000Hz, the hwptr of snd-ymfpci is increase to next boundary (256 frames). so you cannot get accurate playback position. this situation can be emulated with snd-hda-intel by masking the value return by pointer callback with 0xffffff00

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snd-ymfpci only update hwptr in 5.3ms intervals

it seem that snd-usb-audio update hwptr in 1ms

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It seems the options are:-

1. Use 3 periods and accept worse latency, always filling with

avail_frames

snd-ymfpci has periods_min 3 and there are sound cards with periods_max = 2

Yes, this is the sort of thing that makes it more difficult to create a good workaround.

seem only two drivers have this limitation , so you may ask the author of those drivers whether it is feasible to change periods_max to a higher value

drivers/dummy.c: .periods_max = 2, soc/samsung/idma.c: .periods_max = 2,