WL127x SCO MTU not observed

Ryan Erickson

Other Parts Discussed in Thread: WL1271

The wl1271 does not seem to observe the Tx buffer size parameter (HCI_VS_Write_SCO_Configuration) and always returns 120B of data. Do you know of any way to change this? Most headsets I have tried negotiate an MTU of 48B.

The HCI_VS_Write_SCO_Configuration command is written immediately after the hciattach call. This command also includes the “Connection type” field which sets the SCO routing to HCI (The default is PCM).

After programming, hciconfig shows the programmed TX packet length value in its SCO MTU field, but the buffers read from the device seem fixed at 120B.

over 11 years ago

0 Sundeep Javvaji over 11 years ago

TI__Mastermind 32615 points

Hi,

I think if you change the TX Buffer Size using the below command. It should change.

http://processors.wiki.ti.com/index.php/CC256x_VS_HCI_Commands#HCI_VS_Write_SCO_Configuration_.280xFE10.29

You can read the maximum size of the data using the command HCI_Read_Buffer_Size (as per the BT spec)

0 Dotan Ziv over 11 years ago

TI__Expert 5840 points

Hi Ryan,

This internal debug command is not the way to change the buffer size.

As defined by the BT spec, the host should use "HCI_Host_Buffer_Size" command to limit the controller buffer size. The command defines the number of SCO buffers the host has and what is the maximal packet size the controller can use.

For more information, please refer to BT spec (BT 4.0), section 7.3.39 - Host Buffer Size Command.

Note that 120 byte is exactly 1 eSCO packet (over the air after the CVSD encoding), I don't think that 48 bytes a good choise.

Regards,

Dotan

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WL127x SCO MTU not observed