Unable to allocate TX context when calling bt_gatt_notify()

[Bilal]

We are trying to send a large message via a BLE characteristic and to do that we have broken up the message payload into smaller fragments and calling bt_gatt_notify() repeatedly to update the attribute value we are interested in.

We notice there are certain cases where after a few calls to bt_gatt_notify() we get the following error:

<err> bt_conn: Unable to allocate TX context

I assume this is most likely due to a buffer size defined in the config settings that needs to be updated, but we are not sure what exactly needs to updated for this type of error.

Any help would be appreciated, 

Thanks

BTW, we are using nRF Connect v1.8.0 with Zephyr SDK on v2.7.0

[Vidar Berg]

Hello,

A larger CONFIG_BT_BUF_ACL_TX_COUNT value should allow you to queue up more packets. However, with a large enough payload, you may still run out of buffers if bt_gatt_notify() is just being called repeatedly in a loop. if that happens, you will have to wait until the buffers are freed before trying to send again (buffers are freed when the notifications are transmitted).

Best regards,

Vidar