Howto read Voice Data from Amazon Fire TV Remote Control?

Question

I am using a Fire TV Remote Control Version 1, the old one which has no volume and power buttons.

What I want to achieve is, receive audio samples from the build in mic of this remote.

I am using a Raspberry Pi 4 with debian

Linux raspi4box 5.4.79-v7l+ #1373 SMP Mon Nov 23 13:27:40 GMT 2020 armv7l GNU/Linux

I have paired the Remote with bluetoothctl successfully and can read the key events. When the Mic button is pressed, i want to establish a connect to the device and read audio. I can receive the Mic button events correctly so far.

bluetoothctl -- info FC:65:DE:E8:E8:FD

Name: Amazon Fire TV Remote
Alias: Amazon Fire TV Remote
Class: 0x00001f00
Paired: yes
Trusted: yes
Blocked: no
Connected: yes
LegacyPairing: no
UUID: Serial Port               (00001101-0000-1000-8000-00805f9b34fb)
UUID: Human Interface Device... (00001124-0000-1000-8000-00805f9b34fb)
UUID: PnP Information           (00001200-0000-1000-8000-00805f9b34fb)
Modalias: usb:v1949p0410d0304

sdptool browse FC:65:DE:E8:E8:FD

Browsing FC:65:DE:E8:E8:FD ...
Service Name: SPPSERVER
Service RecHandle: 0x20000002
Service Class ID List:
  UUID 128: 00001101-0000-1000-8000-00805f9b34fb
Protocol Descriptor List:
  "L2CAP" (0x0100)
 "RFCOMM" (0x0003)
    Channel: 6
Language Base Attr List:
  code_ISO639: 0x656e
  encoding:    0x6a
  base_offset: 0x100

As You can see, the Remote exposes a Serial Port Profile.

I can connect to the service with:

sudo rfcomm connect /dev/rfcomm1 FC:65:DE:E8:E8:FD 1
...
Connected /dev/rfcomm1 to FC:65:DE:E8:E8:FD on channel 1
Press CTRL-C for hangup

I can use a teminal programm on /dev/rfcomm1 which comes up with a request from the remote:

AT+BRSF=253

At this point you should be able to answer the request and finally initiate the recording on channel 6.

At this point i am stuck, because i get not further response from the device.

Regards Dezi