Missing BLE_GATTS_EVT_HVN_TX_COMPLETE events

[TomKeddie]

I can't comment in  https://devzone.nordicsemi.com/f/nordic-q-a/56685/missing-ble_gatts_evt_hvn_tx_complete-events as it is closed but I am also seeing issues with the TX_COMPLETE event. Please keep me informed of progress.

I use a fifo to push handles as I transmit and a pop on TX_COMPLETE.  This fifo is filling at times (perhaps when bt connection is poor).

nrf52832 / sdk15.3 / softdevice6.1.1

    ret_code_t err_code = BLE_ERROR_GATTS_SYS_ATTR_MISSING;
    uint8_t retry_count = 0;
    while(err_code == BLE_ERROR_GATTS_SYS_ATTR_MISSING && retry_count++ < 10) {
        err_code = sd_ble_gatts_hvx(m_conn_handle, &hvx_params);
        if (err_code == BLE_ERROR_GATTS_SYS_ATTR_MISSING) {
            nrf_delay_ms(50);
        }
    }
    if (err_code == NRF_SUCCESS) {
        // push the handle of the characteristic so we can pop it in the txdone callback
        uint32_t write_count = sizeof(cccd_handle);
        ret_code_t err_code2 = app_fifo_write(&m_tx_fifo,
                                              (uint8_t*) &cccd_handle,
                                              &write_count);
        if (err_code2 != NRF_SUCCESS) {
            // debug for https://github.com/ProxxiTech/proxxiband-fw-nrf52/issues/166
            // and https://github.com/ProxxiTech/proxxiband-fw-nrf52/issues/104
            prx_error_handler_metadata_t metadata;
            metadata.u16[0] = m_tx_fifo.read_pos;
            metadata.u16[1] = m_tx_fifo.write_pos;
            metadata.u16[2] = m_tx_fifo.buf_size_mask;
            prx_error_handler_set_metadata(&metadata);
        }

        APP_ERROR_CHECK(err_code2);
        APP_ERROR_CHECK_BOOL(write_count == sizeof(cccd_handle));
    }

        case BLE_GATTS_EVT_HVN_TX_COMPLETE:
        {
            for (uint32_t count = 0; count < p_ble_evt->evt.gatts_evt.params.hvn_tx_complete.count; count++) {
                uint16_t handle = 0; 
                uint32_t size = sizeof(handle);
                ret_code_t err_code = app_fifo_read(&m_tx_fifo,
                                                    (uint8_t*) &handle,
                                                    &size);
                APP_ERROR_CHECK(err_code);
                APP_ERROR_CHECK_BOOL(size == sizeof(handle));
                ble_ems_char_t* p_char = ble_ems_get_characteristic(handle);
                if (p_char != NULL) {
                    ble_ems_on_tx_complete(p_char);
                }
            }
        }

I asked to have the handles returned from the callback over a year ago, this would be so much easier.

https://devzone.nordicsemi.com/f/nordic-q-a/37979/identifying-the-source-of-a-callback-defined-with-nrf_sdh_ble_observer

[ovrebekk]

Hi Tom

Thanks for the update, that explains why you will see an overflow even if you have 32 entries in the FIFO. 

TomKeddie said:

If I can read the queue water mark dynamically I can ensure low priority characteristics don't starve high priority ones by ensuring there is always some space in the queue.

I think the best workaround here is to upload data freely until the NRF_ERROR_RESOURCES error occurs, wait for the BLE_GATTS_EVT_HVN_TX_COMPLETE event, and then check in with your higher priority characteristics first before you service the low priority ones. 

If you need to maximize bandwidth while allocating a different percentage of the bandwidth to each characteristic you probably need some layer in between the Bluetooth stack and the characteristic updates to handle this prioritization. 

Best regards
Torbjørn