On Thu, Jul 15, 2021 at 12:40 PM Jerome Brunet <jbrunet@xxxxxxxxxxxx> wrote: > > > On Thu 15 Jul 2021 at 14:36, Pavel Hofman <pavel.hofman@xxxxxxxxxxx> wrote: > > > Dne 15. 07. 21 v 11:39 Jerome Brunet napsal(a): > >> On Tue 13 Jul 2021 at 15:16, Pavel Hofman <pavel.hofman@xxxxxxxxxxx> > >> wrote: > >> > > >> So 48kHz / 2ch / 16bits. Let's assume USB_SPEED_FULL for example (result > >> is the same for the other speeds). > >> In such condition, the nominal packet size is 192B but to accomodate an > >> extra sample, the maximum should indeed be 196B. > >> if (!is_playback && (uac2_opts->c_sync == USB_ENDPOINT_SYNC_ASYNC)) > >> srate = srate * (1000 + uac2_opts->fb_max) / 1000; > >> with fb_max being 5 by default, srate should be 48240 after this. > >> > >> max_size_bw = num_channels(chmask) * ssize * > >> DIV_ROUND_UP(srate, factor / (1 << (bInterval - 1))); > >> With USB_SPEED_FULL, bInterval is 1 and factor is 1000 so: > >> => DIV_ROUND_UP(48240, 1000 / 1) should give 49; > >> Then > >> => max_size_bw = 2 * 2 * 49 = 196 > >> So the end result should be 196 with current code. I tried on an ARM64 > >> platform. Here is what I get: > >> [ 26.241946] set_ep_max_packet_size: speed is USB_SPEED_FULL > >> [ 26.243208] set_ep_max_packet_size: intermediate Playback srate 48000 > >> [ 26.249758] set_ep_max_packet_size: max_size_bw 192 > >> [ 26.254559] set_ep_max_packet_size: speed is USB_SPEED_FULL > >> [ 26.260130] set_ep_max_packet_size: intermediate Capture srate 48240 > >> [ 26.266401] set_ep_max_packet_size: max_size_bw 196 > >> [ 26.271209] set_ep_max_packet_size: speed is USB_SPEED_HIGH > >> [ 26.276873] set_ep_max_packet_size: intermediate Playback srate 48000 > >> [ 26.283165] set_ep_max_packet_size: max_size_bw 192 > >> [ 26.288015] set_ep_max_packet_size: speed is USB_SPEED_HIGH > >> [ 26.293691] set_ep_max_packet_size: intermediate Capture srate 48240 > >> [ 26.299965] set_ep_max_packet_size: max_size_bw 196 > >> [ 26.304753] set_ep_max_packet_size: speed is USB_SPEED_SUPER > >> [ 26.310426] set_ep_max_packet_size: intermediate Playback srate 48000 > >> [ 26.316805] set_ep_max_packet_size: max_size_bw 192 > >> [ 26.321625] set_ep_max_packet_size: speed is USB_SPEED_SUPER > >> [ 26.327309] set_ep_max_packet_size: intermediate Capture srate 48240 > >> [ 26.333613] set_ep_max_packet_size: max_size_bw 196 > >> All seems OK and as expected with what's in mainline ATM. > >> So I'm not quite sure why you would get a different result. It would be > >> great if you could check further. > >> > > > > The problem is max_size_bw=192 for the Playback (i.e. is_playback = > > true). If only capture direction is activated (p_chmask=0), only EP-OUT > > with max_size_bw=196 is generated and Win10 enumerates the playback-only > > audio device. > > Ok, that was not clear before. > > > Once the other direction with max_size_bw=192 is activated > > (either duplex or capture-only), Win10 refuses to enumerate. > > Looking further at the format specification [0] (and crawling the web to > decipher it), it seems that > > * For isochronous links: packet size must match the nominal rate. > * For async and adaptative: it must match the nominal rate +/- 1 > packet. That is whether we intend on varying the packet size or not. > > This has several implication > * In async mode, the device is running of its own clock. It has no > reason to vary the playback packet size but it should still reserve > bandwidth for an extra packet to satisfy the spec. This seems to be > your problem and what Win10 insist on. > > When I tested, I had linux on both sides and apparently it is not too > picky about that. > > * If we apply the spec strictly, like Win10 seems to insist on, > calculating the maximum packet size based on explicit feedback limits > is wrong too. Whatever happens, it should be +/- 1 around nominal. > IIRC, a couple of years ago, Alan proposed a smart scheme to keep the UAC2 byterate in exact sync with what's expected over time. You may have to dig into the alsa archives though. cheers.
