How to route SCO over PCM?

[adang322]

Hi,
I would like to route the SCO over PCM but not HCI, but have no idea how to configure it in bluez-alsa.
Any ones know it?
Thank you!

[StuartIanNaylor]

Dunno really as been trying to get HFP/HSP profles working that in #306.
Can you get hfp/hsp profiles working over HCI?
I just get

Mar 11 00:22:54 raspberrypi /usr/bin/bluealsa: ../../src/bluealsa-dbus.c:172: Called: org.bluealsa.Manager1.GetPCMs()
Mar 11 00:22:54 raspberrypi bluealsa[365]: /usr/bin/bluealsa: 279.401448574: D: ../../src/bluealsa-dbus.c:172: Called: org.bluealsa.Manager1.GetPCMs()
Mar 11 00:22:54 raspberrypi /usr/bin/bluealsa: ../../src/bluealsa-dbus.c:373: Called: org.bluealsa.PCM1.Open()
Mar 11 00:22:54 raspberrypi bluealsa[365]: /usr/bin/bluealsa: 279.414051407: D: ../../src/bluealsa-dbus.c:373: Called: org.bluealsa.PCM1.Open()
Mar 11 00:22:54 raspberrypi bluealsa[365]: /usr/bin/bluealsa: 279.415505463: E: Couldn't establish SCO link: Protocol not supported
M

Guess the old bluez details might tell you as not sure as there is also the old bluetooth-alsa that might give some ideas as it used to be a kernel module bt_sco but don't even know where its handled
https://www.kernel.org/doc/ols/2008/ols2008v1-pages-193-196.pdf
https://sourceforge.net/projects/bluetooth-alsa/

Anyway enough of my ignorance, but so want sco for HFP/HSP profiles

[adang322]

Yes. i can get hfp/hsp profiles working over HCI. (bluez5.34 + bluez-alsa).

I would like to route SCO over PCM(TDM/I2S), but I don't know where to configure it in bluez-alsa.
I found that in bluez4.101, there is an option "SCORouting" for SCO can be set to PCM or HCI in audio.conf, but it seems that it was removed in new version.

[StuartIanNaylor]

So its almost the oppisite of the pcm fix for the Pi
raspberrypi/linux#2229 (comment)
I know sudo hcitool cmd 0x3F 0x01C 0x01 0x02 0x00 0x01 0x01 swaps from pcm to hci for the broadcom BT.

I dunno but presuming the routing now is a hardware thing? As above.
Even on the pi I don't actually know which octet swaps between pcm and hci but presume one of them does.
http://dubsman.gitlab.io/posts/what-the-hell-does-hci-tool-do.html
Just seems totally dependent on hardware.
https://www.freedesktop.org/wiki/Software/PulseAudio/Documentation/User/Bluetooth/#index10h3

Apols but at a guess its prob something you can do if you can get the hci cmd for your hardware.

I have a PI4 but using a USB dongle as think on raspberry even if you fix the routing it still has a MTU fault so you get pops and hissing as its fixed on the pi @ 64 but is usually setup as 48.

PS what distro/hardware you using?

[adang322]

My hardware: dspg(soc) + Realtek(USB BT).

[adang322]

I disabled below codes in function "io_thread_sco(..)" for testing.
/*if (release) { t->release(t); asrs.frames = 0; } else */

and then run "dbus-send --system --type=method_call --print-reply --dest=org.bluealsa /org/bluealsa/hci0/dev_XX_XX_XX_XX_XX_XX/sco org.bluealsa.PCM1.Open string:sink (or source)" to open SCO connect only. No need spk_pcm and mic_pcm. then play audio through PCM(TDM) interface, it will be ok.