Will bluetooth stack(nRF51) handle automatic retires to app?

[nordicdev]

Hi, I am using nRF51822xxaa and s130 and SDK 10.0. nRF51 connects with the app(notifications enabled), then bonds with it. Subsequent communications between the app and the nRF51 would happen only if the app and nRF51 are already bonded. Every time when the nRF51 sends a data to the app, should the nRF51 wait in a loop till BLE_EVT_TX_COMPLETE event is received (meaning, the app has received the data that has been sent by the nRF51 to the app)? I thought this would be automatically handled by the Bluetooth stack. Am I right? Thanks.

[Petter Myhre]

I don't understand. What do you think is handled automatically by the SoftDevice? Every time you call sd_ble_gatts_hvx() with NRF_SUCCESS a notification will be put into the packet buffer. Every time one or more notifications are sent you will receive the BLE_EVT_TX_COMPLETE event.

[nordicdev]

Hi Petter, thanks for the reply. Sorry for not being clear. Lets say for example, the nRF51 sends data1 to a connected, bonded app. This data1 was received by the app and the app would get a notification when data1 arrives in the app. This way, the app need not poll to see if any data was received from the nRF51. After a while, data2 is sent by the nRF51 to the app. This time, for some reason, the app has not received the data2. Will the softdevice of nRF51 know that the app has not received the data2? If yes, will the softdevice do retries for a few times till it receives an ack (or something of that sort) from the app (that app has received data2 from the nRF51)?

[Petter Myhre]

Notifications are only acknowledged at the link layer, and the SoftDevice will handle retransmissions. The SoftDevice doesn't know if the app has received the notification, the SoftDevice only knows that the notification has been successfully transferred to the peer's link layer.

If you want the app to acknowledge each packet, you should use indication instead of notification.

Please see this for more information.

[nordicdev]

This is what I wanted to know. May I know how many attempts of retransmissions does the softdevice do for notifications (in case there is a packet failure from nRF51 to peer's link layer) Thanks!

[Petter Myhre]

It will retransmit the packet until supervision timeout is reached, then the connection shall be considered lost.