How to check when the stack is ready to send notification?

[Dmitry Kr]

Hi all,

I'm using two nRF51 DK to measure ADC input on peripheral side and translate it to central, based on Multilink example. One software timer is used to perform one ADC conversion every 1 sec, and send a notification to the central throug sd_ble_gatts_hvx(). Currently timer started and stopped by button press, I need to change it:

• start timer, when connection is done AND notification is properly enabled;
• stop timer, when notification disabled or connection is done.

What BLE events or functions should be used to get this done?

Currently I check:

1. (m_conn_handle != BLE_CONN_HANDLE_INVALID) in timer handler - it doen's works when connection is done, handle still has the value

2. err_code = sd_ble_gatts_hvx(m_conn_handle, &hvx_params);
    if (err_code != NRF_ERROR_INVALID_STATE && err_code !=     BLE_ERROR_GATTS_SYS_ATTR_MISSING)         
    {
        APP_ERROR_CHECK(err_code);
    }
   

[Dmitry Kr]

Hi, Anders!

Thank you, it works fine for cccd writes, but there is an error produced on the disconnection, althought BLE_GAP_EVT_DISCONNECTED is monitored. I get the 0x3004 error on the code:

err_code = sd_ble_gatts_hvx(m_conn_handle, &hvx_params);
if (err_code != NRF_ERROR_INVALID_STATE && err_code != BLE_ERROR_GATTS_SYS_ATTR_MISSING) {
APP_ERROR_CHECK(err_code);
}

The problem typically appears on small timer period (I tested for 100 ms), when I reset central app. What is wrong here?

[Anders Strand]

The 0x3004 error is BLE_ERROR_NO_TX_BUFFERS. It is returned when you have no free output buffers to put a packet in. I makes sense that you get this error if you keep trying to send notifications, but the central is off. The packets you put in the buffer after the central is turned off will be stuck there.

[Dmitry Kr]

Dear Anders, you totally right! Ok, the question is recommendation for program behavior getting this error. Curretnly APP_ERROR_CHECK stops the program or resets CPU depending on debug macro setting. What we should do getting this error code? Could we ignore it?

[Dmitry Kr]

Would we made the TX buffer like one in HRS_C example, with re-sending packets got this error?

[Anders Strand]

Since the central is off, the packets are not leaving the TX buffer. Adding more buffers will not help you. In your case, this error can be viewed as a symptom of a disconnect. The disconnect event will not happen before a certain amount of connection intervals have passed (this time is often defined as CONN_SUP_TIMEOUT in our SDK). You can ignore the error if you want, or you can pause the sending of packets until you receive a BLE_EVT_TX_COMPLETE

[Dmitry Kr]

Andre, thanks a lot. Also, I receive the same error when trying to set faster send period. If I try to send packets frequenly than 100 ms, the same error received. Why this happens if central settings is:

MIN_CONNECTION_INTERVAL          MSEC_TO_UNITS(30, UNIT_1_25_MS)                
MAX_CONNECTION_INTERVAL          MSEC_TO_UNITS(60, UNIT_1_25_MS)                
SLAVE_LATENCY                    0                                              
SUPERVISION_TIMEOUT              MSEC_TO_UNITS(4000, UNIT_10_MS)