Dne 30. 04. 21 v 16:26 Jerome Brunet napsal(a): > From: Ruslan Bilovol <ruslan.bilovol@xxxxxxxxx> > > As per USB and UAC2 specs, asynchronous audio sink endpoint > requires explicit synchronization mechanism (Isochronous > Feedback Endpoint) > > Implement feedback companion endpoint for ISO OUT endpoint > > This patch adds all required infrastructure and USB requests > handling for feedback endpoint. Syncrhonization itself is > still dummy (feedback ep always reports 'nomimal frequency' > e.g. no adjustement is needed). This satisfies hosts that > require feedback endpoint (like Win10) and poll it periodically > > Actual synchronization mechanism should be implemented > separately > > Signed-off-by: Ruslan Bilovol <ruslan.bilovol@xxxxxxxxx> > Signed-off-by: Jerome Brunet <jbrunet@xxxxxxxxxxxx> Hi, The HS calculation of Q16.16 feedback value overflows at some 524kHz, disallowing use of larger samplerates (e.g. 768kHz or higher). I tested the formula used in alsa USB driver https://github.com/torvalds/linux/blob/d99676af540c2dc829999928fb81c58c80a1dce4/sound/usb/endpoint.c#L80 which uses only 10bit shift. The feedback control in UAC2 gadget now works up to 4M samplerate with 1Hz precision (tested on RPi4 with bInterval = 1, checked in stream0 proc file on linux host). --- a/drivers/usb/gadget/function/u_audio.c +++ b/drivers/usb/gadget/function/u_audio.c @@ -118,7 +119,8 @@ static void u_audio_set_fback_frequency(enum usb_device_speed speed, * Prevent integer overflow by calculating in Q12.13 format and * then shifting to Q16.16 */ - ff = DIV_ROUND_UP((freq << 13), (8*1000)) << 3; + ff = ((freq << 10) + 62) / 125; } *(__le32 *)buf = cpu_to_le32(ff); } Best regards, Pavel.
