Error codes for sd_ble_gatts_hvx

[Ivan Jug]

I am trying to send just random dummy data to my android app. 
First of all, I am not expecting or need the confirmation, so I should be using the notification and not indication, because indication requires the confirmation, right?

There are 2 scenarios that are happening. I start sending data without setting notification on Android and I seem to be sending data but getting error 3401. If I got it right this means exactly that, that the other side has no notification enabled?

The other situation is when I enable notification on app side but after 5-6 messages it get error code 13, which means that something timed out?

I am a little bit lost on what I am doing wrong, because my app receives all of those messages. How and what would be correct way to handle this?

[run_ar]

Hi,

You have to check the error message and act accordingly, If you use a for loop you will most likely get NRF_ERROR_RESOURCES, once the buffers are used. Then you have to exit the for loop, and wait for BLE_GATTS_EVT_HVN_TX_COMPLETE before you start calling sd_ble_gatts_hvx again.

See flow chart here: GATTS Handle Value Notification

[Ivan Jug]

Yes, I am getting NRF_ERROR_RESOURCES, forgot hex to decimal conversion. I thought it is NRF_ERROR_TIMEOUT.

Lets say I have something as simple as this. What would be correct way to handle that?

for(int i = 0; i <= 20; i++){
    uint8_t data[] = {5, 0, 0, 0};
    err_code = ble_mds_on_tx_change(m_conn_handle, &m_mds, data);
    
    NRF_LOG_INFO("err_code: %x", err_code);

    if (err_code != NRF_SUCCESS &&
        err_code != BLE_ERROR_INVALID_CONN_HANDLE &&
        err_code != NRF_ERROR_INVALID_STATE &&
        err_code != BLE_ERROR_GATTS_SYS_ATTR_MISSING) {
        APP_ERROR_CHECK(err_code);
    }
}

EDIT:
I am actually now waiting for BLE_GATTS_EVT_HVN_TX_COMPLETE to send new data. However with this the time goes up to 100 ms between data. My goal is to test fastest I can send it, in theory I should be able to do so with 7.5 ms? Would scenario where I would just send data and forget about it be possible?
Also with error I am getting would it be possible to just clear buffer and continue?

[run_ar]

Hi,

You should call sd_ble_gatts_hvx in a loop until you receive NRF_ERROR_RESOURCES. Then wait for the TX_COMPLETE event. That way you can transfer multiple packets in each connectio event. Also note that a TX_COMPLETE event can free several buffers at once.

The other thing is changing the connection interval. The master might not grant you an interval of 7.5 ms, but if it does you can send multiple packet quite fast. But the fastest way is actually to increase packet length, enable connection event extensions and use longer intervals. This is described in the SD spec: Bluetooth Low Energy data throughput