NRF52840 BLE NUS data transmission is too slow

RE: NRF52840 BLE NUS data transmission is too slow

masterLee — Tue, 28 Jun 2022 10:39:13 GMT

Hi, I finally fixed it... The solution is the following modification

size = 243;
for(uint8_t i = 0; i<16; i++)
{
 do{
    nrf_gpio_pin_clear(UART_RX_PIN); // TODO TEST OUTPUT
    err_code = ble_nus_data_send(m_nus_gen, &localBuffer.convPacket[i*size], &size, *m_conn_handle_gen);
    nrf_gpio_pin_set(UART_RX_PIN); // TODO TEST OUTPUT
 }while(err_code == NRF_ERROR_RESOURCES); //while(i <= 16);
}
bleBuffer_is_full = true; 
while(bleBuffer_is_full);

I used to check the bleBuffer_is_full flag after every packet transmission and this was slowing down the whole transmission process. Now I check it only once at the end of the transmission and the speed has increased to 82kBps.
I assume that by changing the connection interval and event length values it will reach 90kBps.

RE: NRF52840 BLE NUS data transmission is too slow

masterLee — Mon, 27 Jun 2022 11:47:53 GMT

Hi, currently I have only one DK so sniffer is not an option at the moment.
But I have found what is causing the issue and I don't know how to solve it.

In the code part that corresponds to the 4096 bytes transmission from the peripheral to the central, I check for NRF_resources error after each packet transmission and I block the code there in that case until a BLE buffer is free and BLE_GATTS_EVT_HVN_TX_COMPLETE event occurs.

The time for one packet transmission, with ble_nus_data_send(), is approximately 200usec and the time between two consecutive transmissions is approximately 25 msec. The whole problem lies in those 25msec.
Is there a way to reduce it?

If I entirely remove the NRF_resources error check and I transmit data continuously the peripheral device crashes.

 size = 243;
       for(uint8_t i = 0; i<16; i++)    //send the cache buffer to tablet in chunks of 128 bytes
       {  
          nrf_gpio_pin_clear(TestPin); 
          err_code = ble_nus_data_send(m_nus_gen, &localBuffer.convPacket[i*size], &size, *m_conn_handle_gen);
          if(err_code = NRF_ERROR_RESOURCES)
          {
             bleBuffer_is_full = true; 
             while(bleBuffer_is_full); 
          }
          nrf_gpio_pin_set(UART_RX_PIN); // TODO TEST OUTPUT
       }
       size = 191;
       err_code = ble_nus_data_send(m_nus_gen, &localBuffer.convPacket[16*size], &size, *m_conn_handle_gen);
       if(err_code = NRF_ERROR_RESOURCES)
       {
          bleBuffer_is_full = true; 
          while(bleBuffer_is_full); 
       }     
       nrf_gpio_pin_set(TestPin);

RE: NRF52840 BLE NUS data transmission is too slow

Jared — Mon, 27 Jun 2022 09:33:36 GMT

NRF_SDH_BLE_GAP_EVENT_LENGTH is set a bit low, have you tried increasing it? Could you use nRF Sniffer and provide the sniffer trace when you send data with your original connection parameters?

RE: NRF52840 BLE NUS data transmission is too slow

masterLee — Fri, 24 Jun 2022 13:55:52 GMT

Hi, no this does not work. In fact it makes the transmission much slower (1.7kB/sec).
With the previous settings the transmission reached 17kB/sec.

RE: NRF52840 BLE NUS data transmission is too slow

Jared — Fri, 24 Jun 2022 13:25:18 GMT

Hi,

Maybe you can try to set the connection parameters as in the throughput example?:

regards

Jared

RE: NRF52840 BLE NUS data transmission is too slow

masterLee — Fri, 24 Jun 2022 10:33:21 GMT

I think I have found the root cause. The time between two packet transfers takes about 25msec. That is the BLE_GATTS_EVT_HVN_TX_COMPLETE event fires every 25msec. So the question is how can I make the transfer faster