SCO send data

[sasha1396]

Hi! I use BtStack with Realtek chip as Bluetooth connected to nRF54l15 across UART. When i use SCO, i dont send data, this case call some times when i started calling on mobile and when i terminated calling on mobile. While calling this case dont call. However i get data success from SCO.

case HCI_EVENT_SCO_CAN_SEND_NOW:
sco_demo_send(sco_handle);
break;

What maybe problem?

One more quetion: how switches bettween A2DP and SCO?

[mringwal]

Hi @sasha1396

Which Realtek Controller do you use?

SCO can be routed over HCI UART or over I2S based on the rtlXXXX_config file use to startup the Controller.
Which rtlXXXX_fw and rtlXXXX_config files did you use?

Please try got collect an HCI trace. On nRF54L15, you normally can use RTT for BTstack's hci_dump.

You don't need to "switch" between A2DP and HFP. If you in the gateway role, e.g. like a mobile phone, you should pause the A2DP stream and enable SCO for HFP when there's an incoming call. You then do the same after the call (disconnect SCO and restart the A2DP Stream).

[sasha1396]

Hi. I figured out the cause. My condition

btstack/src/hci.c

Line 714 in 4bdc72d

if (hci_stack->synchronous_flow_control_enabled){

returns 0. I forced
hci_stack->synchronous_flow_control_enabled = 0 in

btstack/src/hci.c

Line 2997 in 4bdc72d

hci_stack->synchronous_flow_control_enabled = 1;

and now the implicit flow control

btstack/src/hci.c

Line 727 in 4bdc72d

// implicit flow control

condition is met and SCO packets are sent.
I tried disabling flow control using hci_send_cmd(&hci_write_synchronous_flow_control_enable, 1);

btstack/src/hci.c

Line 2160 in 4bdc72d

hci_send_cmd(&hci_write_synchronous_flow_control_enable, 1); // SCO tracking enabled

by writing 0 hci_send_cmd(&hci_write_synchronous_flow_control_enable, 0); but I still get to

btstack/src/hci.c

Line 2997 in 4bdc72d

hci_stack->synchronous_flow_control_enabled = 1;

How can I properly disable flow control for SCO without editing the library code?
My UART currently doesn't have CTS/RTS. Does flow control for SCO imply the presence of CTS/RTS?
I still want to figure out how to do it correctly, is it possible in my case to send SCO with flow control.

[mringwal]

Hi Sasha
BTstack is not designed to work without hardware flow control. If you don't have CTS/RTS (well, BTstack only cares for connecting the MCU RTS to the Bluetooth CTS to pause incoming data), please fix that first. Maybe the issue with SCO Flow Control is a consequence from missing bytes on the UART.

Which Realtek Controller do you use?
Which rtlXXXX_fw and rtlXXXX_config files did you use?
Please try got collect an HCI trace. On nRF54L15, you normally can use RTT for BTstack's hci_dump.