how can an SCO link be reestablished after it has been disconnected by the HF device?

[Sleepalltheday]

Problem

• I have observed that during interactions with certain headset devices using the HFP (Hands-Free Profile), the headset devices tend to disconnect the SCO link upon receiving the call termination indication ("CIEV:2,0").
• After the SCO link is disconnected, bluez-alsa does not automatically initiate a reconnection, and I have not discovered a relevant D-Bus interface to prompt bluez-alsa to establish an SCO connection again.
• I tried using the "SelectCodec" feature to renegotiate the audio encoding, but when bluez-alsa sees the codec hasn't changed, it doesn't do anything.
• In this case, how can I prompt bluez-alsa to re-establish the SCO connection?

Reproduction steps

• bluealsa -p hfp-ag -p a2dp-source
• use bluetoothctl connect to HF device
• run bluealsa-rfcomm, make the call setup "CIEV:2,1"
• send the call end "CIEV:2,0"

Setup

• linux 5.1
• bluealsa --version
  • v4.1.1
• bluetoothd --version
  • 5.56

Additional context

• After a call finishes, the SCO connection gets closed down

bluealsa: D: ba-rfcomm.c:110: Sending AT message: RAW: command:
+BSIR:0
, value:(null)
bluealsa: D: ba-rfcomm.c:110: Sending AT message: RAW: command:
+CIEV:3,3
, value:(null)
bluealsa: D: ba-rfcomm.c:110: Sending AT message: RAW: command:
+CIEV:2,1
, value:(null)
bluealsa: D: ba-rfcomm.c:110: Sending AT message: RAW: command:
+CIEV:3,0
, value:(null)
bluealsa: D: ba-rfcomm.c:110: Sending AT message: RAW: command:
+CIEV:2,0
, value:(null)
bluealsa: D: at.c:179: AT message: CMD: command:+CLCC, value:(null)
bluealsa: D: ba-rfcomm.c:110: Sending AT message: RAW: command:
OK
, value:(null)


bluealsa: D: io.c:46: BT socket disconnected: Connection reset by peer
bluealsa: D: ba-transport.c:462: Closing BT socket duplicate [29]: 31
bluealsa: D: sco.c:504: IO loop: EXIT: sco_msbc_dec_thread: HFP Audio Gateway (mSBC)
bluealsa: D: ba-transport.c:1983: Exiting IO thread [ba-sco-dec]: HFP Audio Gateway (mSBC)
bluealsa: D: ba-transport.c:462: Closing BT socket duplicate [29]: 30
bluealsa: D: ba-transport.c:903: Releasing SCO link: 29
bluealsa: D: ba-transport.c:1983: Exiting IO thread [ba-sco-enc]: HFP Audio Gateway (mSBC)

[Sleepalltheday]

I found that opening the PCM channel can establish the SCO connection, so should I proceed with this approach?

[borine]

I found that opening the PCM channel can establish the SCO connection

When using BlueALSA, that is in fact the only way to establish the SCO connection. There is an example in the wiki of using bluealsa-rfcomm to simulate a phone transferring call audio to a hands-free device; see RFCOMM with HFP, or if you are using an ALSA application you can use a PCM plugin to take care of the rfcomm messages for you; see HFP AG Helper Plugin for BlueALSA

[borine]

closing due to lack of activity