Unable to Increase ACL Packet Size in HCI_USB Sample in nRF Connect SDK

[AhmedPs19]

Hello,

I am using the hci_usb sample from Zephyr and running BlueZ 5.53 on Ubuntu 20.04. I am trying to increase the ACL packet size from the default value of 27 bytes and 3 packets using hcitool, but I am unable to achieve this change.

I have tried various configurations and settings, but it appears that the ACL size remains limited. Could anyone provide guidance on how to increase the ACL packet size beyond this limit?

Regards,
Ahmed

[Sigurd]

Hi!

Try adding this in prj.conf:

CONFIG_BT_BUF_ACL_RX_SIZE=502
CONFIG_BT_ATT_PREPARE_COUNT=2
CONFIG_BT_ATT_TX_COUNT=10
CONFIG_BT_L2CAP_TX_MTU=498
CONFIG_BT_L2CAP_DYNAMIC_CHANNEL=y
CONFIG_BT_CONN_TX_MAX=10
CONFIG_BT_BUF_ACL_TX_COUNT=10
CONFIG_BT_BUF_ACL_TX_SIZE=502

CONFIG_BT_CTLR_DATA_LENGTH_MAX=251
CONFIG_BT_USER_DATA_LEN_UPDATE=y

Also, if you have issues with hci_usb, then you could try compiling hci_uart with the CDC uart driver and use that instead.

[AhmedPs19]

Hi Sigurd,

I am using nRF Connect SDK 2.6 and it is not recognizing CONFIG_BT_ATT_TX_COUNT as a valid configuration parameter. Apart from this one , I have added other configurations and it has increased the ACL.

Can you suggest what is the maximum stable MTU size for this sample ?

Regards,
Ahmed

[Sigurd]

AhmedPs19 said:

I am using nRF Connect SDK 2.6 and it is not recognizing CONFIG_BT_ATT_TX_COUNT

It was changed in later releases.

In 2.6 it's called CONFIG_BT_L2CAP_TX_BUF_COUNT.

If it's still not working, could you provide a sniffer trace for the ATT MTU exchange ?

https://www.nordicsemi.com/Products/Development-tools/nRF-Sniffer-for-Bluetooth-LE