Can you not call sd_ble_gatts_hvx() in a loop?

RE: Can you not call sd_ble_gatts_hvx() in a loop?

Sigurd — Mon, 16 Oct 2017 10:58:29 GMT

Does it work fine when you only use 1 sd_ble_gatts_hvx in the event handler? How big it your hvn_tx_queue_size ?

RE: Can you not call sd_ble_gatts_hvx() in a loop?

Elias — Wed, 11 Oct 2017 16:13:26 GMT

I'm having a different problem with the same piece of code now: is there any reason that calling sd_ble_gatts_hvx() in a loop would prevent transmission? Usually, it works, but there's one scenario in my application where the loop consistently gets stuck with sd_ble_gatts_hvx returning NRF_ERROR_RESOURCES. It looks like a transmission event never happens because I never see the last successful sd_ble_gatts_hvx packet at the peer, and this causes that loop to repeat indefinitely.

I think the unique thing about the scenario is that it's the first time I'm trying two sd_ble_gatts_hvx loops within the same event handler, rather than looping until one packet is queued and then returning control to the SoftDevice before I try another loop.

RE: Can you not call sd_ble_gatts_hvx() in a loop?

Sigurd — Tue, 03 Oct 2017 10:32:35 GMT

Hi,

The number of Handle Value Notifications that can be queued is configured by ble_gatts_conn_cfg_t::hvn_tx_queue_size. When the queue is full, the function sd_ble_gatts_hvx() will return NRF_ERROR_RESOURCES. A BLE_GATTS_EVT_HVN_TX_COMPLETE event will be issued as soon as the transmission of the notification is complete.

You have 2 options, either call sd_ble_gatts_hvx() in a loop until the function returns NRF_SUCCESS, or wait for the BLE_GATTS_EVT_HVN_TX_COMPLETE and then send the next packet. There is no race condition here.