ble_nus_data_send error occurs sometimes.

[_maibi]

MCU: nrf52840

SDK: V 15.2.0 porting with nRF-IEEE-802.15.4-radio-driver

problem:

ble_nus_data_send function sometimes returns BLE_ERROR_GATTS_SYS_ATTR_MISSING error. and also even if returns NRF_SUCCESS, Sometimes not properly works. - ONLY PHONE BLE TURNED ON FIRST CONNECTION (I PHONE 6S+) 

after first failure, next try. it works good. -> back to the first, my i phone turn off bluetooth, turn on and retry, also this issue is repeated.

analyzation: 

when communication failed, ble evt id : 0x50 (i guesses BLE_GATTS_EVT_WRITE) is called ONLY ONCE at the moment of connection.

But, when succeed, this event id is called always TWICE.

background: 

We has already nRF51822 production. but this issue isn't occurred. evt id : 0x50 is always called twice.

Questions:

1) What is role of ble evt id : 0x50 (BLE_GATTS_EVT_WRITE) and Why it is called always twice ?

2) what is relationship between BLE_ERROR_GATTS_SYS_ATTR_MISSING error and phenomenon called only once ( 0x50).

3) how can I handle this issue? 

I'm not sure this assumption. only phenomenon. I would appreciate your advice. thanks.

[bjorn-spockeli]

Q1: The BLE_GATTS_EVT_WRITE event is generated by the SoftDevice when a Ble Central has written to one of the characteristics on the Ble peripheral. Hence, it is called twice because characteristics are written to. 

Q2: Are you calling ble_nus_data_send() before you have called ble_stack_init? If that is the case then you might get,  BLE_ERROR_GATTS_SYS_ATTR_MISSING return code. 

Q3: Provide us with a sniffer trace of the on air packets using a Ble protocol analyzer or the nRF Sniffer. 

Best regards

Bjørn

[_maibi]

thanks for the answer.

Q1. does your mention mean that  BLE_GATTS_EVT_WRITE event is always dependent on Central Device (My case SmartPhone)?

Q2, No, I always call ble_stack_init at the cold boot. but sometimes ble_nus_data_send returns BLE_ERROR_GATTS_SYS_ATTR_MISSING.

Q3. Ok. I will do this.

[bjorn-spockeli]

Q1: Yes, the BLE_GATTS_EVT_WRITE is only generated when a BLE central is writting to the characteristics /descriptors on the ble peripheral. 

Q2: Are you bonding with the smartphone you are trying to notify?

Q3. OK

Best regards

Bjørn

[_maibi]

It's been a long time. I know second of BLE_GATTS_EVT_WRITE event after a while. so I wait to receive twice BLE_GATTS_EVT_WRITE, it works, nus_put function doesn't occur BLE_ERROR_GATTS_SYS_ATTR_MISSING error.

Is it timing issue? Why I wait BLE_GATTS_EVT_WRITE  event received twice? What is role of BLE_GATTS_EVT_WRITE  event?

[bjorn-spockeli]

_maibi:  As previously stated you will get the BLE_GATTS_EVT_WRITE  event when a BLE Central has written to a characteristic present on the BLE peripheral. 
When you're referring to nus_put , do you mean ble_nus_data_send()?

In order to help you we need to see a sniffer trace of the on air data.