Audio connection failed with error 0x7F

[Eduard Sik]

Dear BTstack developers,

I'm implementing HFP HF on ESP32 using BTstack. When trying to establish an audio connection with command 'b' after pairing with a phone, I receive error 0x7F:

Copy

Establish Audio connection to device with Bluetooth address 2C:BE:EB:17:2E:5B... Audio connection establishment failed with status 0x7f

The error code 0x7F (HCI_ERROR_INSTANT_PASSED) suggests a timing issue during SCO link setup. Is this a known issue with ESP32's Bluetooth controller? What configuration changes are needed to establish a stable SCO audio connection?

Details:

• Hardware: ESP32
• BTstack version: Latest
• Profile: HFP-HF
• Connection type: eSCO/SCO
• Remote device: Android phone

Thank you for your help!

[Matthias Ringwald]

Hi Edouard

For HFP, you first need to establish the Service Level Connection. After that you can open the Audio Connection. Please keep in mind that the Audio connection is usually opened by the AG device, and iOS & Android don't accept it. Also: what audio would you expect to receive from a mobile phone? Please start a voice recording application, or, make a phone call or so.

Cheers
Matthias

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