On Mon, 19 Apr 2021 at 18:00, Shreyansh Chouhan < [email protected]> wrote:
> > On Fri, 16 Apr 2021 at 17:02, Gerd Hoffmann <[email protected]> wrote: > >> Hi, >> >> > I learned that the callback passed in AUD_open_out, (lets call it the >> write >> > audio callback,) is supposed to mix and write the >> > buffers to HWVoiceOut. I have written that, the basic algorithm being: >> > >> > 1. Pop element from tx virtqueue. >> > 2. Get the xfer header from the elem->out_sg (iov_to_buf(elem->out_sg, >> 1, >> > 0, &hdr, sizeof(hdr))) >> > 3. Get the buffer from elem->out_sg (iov_to_buf(elem->out_sg, 1, >> > sizeof(hdr), &mixbuf, period_bytes)) >> > 4. AUD_write the buffer >> >> AUD_write returns the number of bytes actually accepted. >> >> In case the audio backend consumed the complete buffer you can go ahead >> as described. Otherwise stop here and resume (try AUD_write() the >> remaining data) when the callback is called again. >> > The callback that is supposed to write the buffers to HWVoiceOut has to > do it such that it only writes the buffers for the streams that it was > called by. The tx > virtqueue is going to have buffers for all the streams. How do I handle > this situation? > > Say, I have 3 output streams 0, 1 and 2, the callback was called on stream > 0, how do > I only play buffers corresponding to this stream? Is there a way by which > I could iterate over > the virtqeueue? > > If not then I should probably store the VirtQueueElements corresponding to > a specific stream > in the stream itself. I have to store the elements because I'd have to > write to the response and > mark these elements as used, (via virtqueue_push i think.) > > Also, is virtqueue a 'queue'? I remember reading in the specs that the > device can consume > the buffers in any order it prefers unless a feature bit is negotiated. So > does virtqueue_pop > always return the first element that entered the queue? (FIFO?) > > If it is FIFO, then I think the only way would be to iterate over the > virtqueue. However if `virtqueu_pop` > does return the last inserted element, I can use `handle_tx` > to get the last element inserted and then add it to the corresponding stream. Sorry for the incomplete mail. I don't know how I hit send. > > >> No problem. I'm likewise busy or on (easter) vacation at times and fail >> to send timely answers (sorry for that). >> > Also that's fine, I just got a bit worried :) I think once this `tx` part is done I'll have the pcm streams ready, and I can send in patches by tonight or tomorrow evening latest. > >> HTH & take care, >> Gerd >> >>
