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CC2564C: BT Classic for A2DP: How to request a specific Baseband packet type (2-DH5) for each L2CAP transmission of AVDTP audio data? I want to use single 2-DH5 instead of {2-DH5 + 2-DH3} combination

user5975851
Prodigy 120 points
Part Number: CC2564C

Hi TI Forum,

By default our implementation of A2DP source based on TI CC2564C transmit AVDTP audio data over BT Classic using a baseband packet combination of {2-DH5 + 2-DH3}. Instead we would like to use only 2-DH5 baseband packets.

Here's our A2DP Source configuration:

Audio encoder: SBC
Audio sampling: 48kHz
SBC Bitpool: 51
SBC allocation method: Loudness
SBC Channel mode: Joint Stereo
SBC subbands: 8
Audio sample size: 102 Bytes

TI CC2564C takes 7 audio samples to build each AVDTP Media Packet of 818 Bytes.

L2CAP is 822 Bytes and carries the above AVDTP Media Packet of 818B.

Those L2CAP 822 Bytes are spread into the following Baseband packets:

  • 679B into 2-DH5 payload
  • 143B into 2-DH3 payload

Here's a screenshot of a BT trace from our Ellisys sniffer:

Ideally we would like TI CC2564C to only take 5 audio samples to build AVDTP Media Packets of 588 Bytes.

L2CAP would be 592 Bytes

Those L2CAP 592 Bytes could be carried into:

  • a single 2-DH5 payload (maximum payload capacity of 679B)

Any piece of advice to perform this?
How can we request TI CC2564C to only take 5 audio samples instead of 7?

Thanks in advance for your suggestions,

JiBé.

  • 0
    TI__Expert 5285 points
    Hi,

    Due to the fact that the CC2564C is performing other tasks at the same time, scanning, etc...
    It will use a different combination of packets in order to optimize the usage of the time line.

    You can try to limit the packets supported:

    Send_HCI_Change_Connection_Packet_Type Handle, 0x0C18

    and choose the specific packets you'd like to use.

    Chen Loewy
  • 0 in reply to Chen Loewy
    Prodigy 120 points

    Hi Chen,

    Thank you for your suggestion.

    Unfortunately disabling the baseband packet 2-DH3 did not have the intended consequence.

    Let me give you some details:

    As you suggested we used the HCI command Change_Connection_Packet_Type. To disable 2-DH3 and leave all other packet types enabled we use bitmask parameter 0xCD18.

    I was hoping TI CC2564C would use single packets of 2-DH5 carrying 5 Audio Frames at Bitpool 51 and Sampling 48kHz.

    Instead TI CC2564C was using combination of {2-DH5 + 2-DH5} carrying 7 Audio Frames at Bitpool 51 and Sampling 48kHz.

    Here's the Ellisys sniffer log snippet:

    Please would you have any other suggestions on how we could request TI CC2564C to only get 5 audio frames at a time in order to have TI CC2564C only uses single packets of 2-DH5?

    If you look at how Apple iPhones and Google Pixels stream A2DP, they only pick 5 audio frames at a time. Then they carry them over a single 2-DH5 baseband packet. As an A2DP source we would like to do the same. This present advantages in poor RF environment with combination of high pathloss and high interference on the 2.4GHz band.

    Thanks in advance for your suggestions,

    -JiBé.