Can bt_nus_send be called multiple times within a single connection interval?

[qianjunwang]

Hello,

If I set the connection interval to 300ms, can I call bt_nus_send multiple times (e.g., every 100ms) within that interval?

Additionally:

How can I check if the FIFO queue is empty (i.e., ready to accept new data without overflow)?

Context:

I'm developing a BLE device that needs to:

Maintain active scanning (cannot use very short connection intervals, e.g., <30ms).

Maximize data throughput using bt_nus_send over an existing connection.

Best regards,
Qianjun Wang

[Einar Thorsrud]

Hi,

Yes, you can call bt_nus_send() repeatedly. If the buffer is full, you will get -ENOMEM returned and will have to try again laiter.

There is n API to see the number of queued packets, but you can register the sent callback for the NUS service and count yourself if you need this information (incrase a variable wen you call bt_nus_send() successfully, and decrease it when you get the callback).

[hmolesworth]

As an aside, following eith's suggestion be aware that if you do not implement such a count or something similar a BLE disconnect followed by a reconnect will silently discard the buffer contents at the time of BLE disconnect (in our experience, may be different with latest Softdevice/IDEs) and those packets discarded will be lost. Tracking received packets allows reloading the buffer and hence BLE transmission.