Passing Characteristic data to Function

RE: Passing Characteristic data to Function

Aftab — Mon, 15 Apr 2019 11:01:42 GMT

I have changed three things which corrected this error:

1. defined the variable global_flag as volatile

2. Defined this variable in the service file and used it elsewhere

3. Defined the arrays which data from service is used to be fixed length. Like instead of defining char array[]=""; I defined like char array[10];

It's strange but it solved the issue.

RE: Passing Characteristic data to Function

cbd — Thu, 11 Apr 2019 13:13:26 GMT

It sounds to me that you're encountering an access conflict.

Below is a section of code for one of my services.

lds_drive_data_t is a data structure that I transfer using one of the service characteristics.

In the bottom of the code you can see that I set a global structure

volatile lds_uart_data_t m_lds_RX_data;

. Note that I have declared it volatile.

Depending on what is received during the event data is passed to functions pointed to by lds_write_handler or lds_uart_rx_handler

static void lds_OnWrite(ble_lds_t * p_lds, ble_evt_t const * p_ble_evt)
{
    VERIFY_PARAM_NOT_NULL_VOID(p_lds);
    VERIFY_PARAM_NOT_NULL_VOID(p_ble_evt);

    /* get the write event data */
    ble_gatts_evt_write_t const * p_evt_write = &p_ble_evt->evt.gatts_evt.params.write;
    lds_drive_data_t newData = {0};
    /* confirm that characteristic was written to, data length is correct and
    that an event handler has been set */
    if ((p_evt_write->handle == p_lds->lds_char_handles.value_handle) &&
        (sizeof(newData.command) <= p_evt_write->len) && (p_lds->lds_write_handler != NULL))
    {
        memcpy(&newData.command, p_evt_write->data, sizeof(newData.command));
        newData.dataLength = p_evt_write->data[sizeof(newData.command)];
        if (newData.dataLength > 0)
        {
            memcpy(&newData.data,
                   p_evt_write->data + sizeof(newData.command) + sizeof(newData.dataLength),
                   p_evt_write->len - (sizeof(newData.command) + sizeof(newData.dataLength)));
        }
        /* pass write event data to the event handler */
        p_lds->lds_write_handler(p_lds, newData);
    }
    else
    {
        if ((p_evt_write->handle == p_lds->lds_uart_rx_handles.value_handle) &&
        (0 <= p_evt_write->len) && (p_lds->lds_uart_rx_handler != NULL))
        {
            m_lds_RX_data.length = p_evt_write->len;
            m_lds_RX_data.p_data = p_evt_write->data;
        
            /* pass write event data to the event handler */
            p_lds->lds_uart_rx_handler(p_lds, m_lds_RX_data);
        }
    }
}

I don't poll for data within the rest of my code at the moment, but if you can't glean anything from my code then you may need to takes steps to prevent access conflicts on the basis that the SoftDevice should take priority over everything else and shouldn't be held up in anyway otherwise it will suffer internal timeouts and the BLE will stop working.

RE: Passing Characteristic data to Function

Aftab — Thu, 11 Apr 2019 11:21:33 GMT

I have also tried to implement following code to read characteristic value.

void get_script_start_flag(){
    uint8_t testStore;
    ble_gatts_value_t testStruct;

    testStruct.p_value = &testStore;
    testStruct.len = 2;
    testStruct.offset = 0;

    sd_ble_gatts_value_get(scr_service_instance->conn_handle, scr_service_instance->char_handles_1.value_handle, &testStruct);
    //NRF_LOG_INFO("testStruc: %X,%X", testStruct.p_value[0], testStruct.p_value[1]);
    //return testStruct.p_value[0];
    script_start_flag = testStruct.p_value[0];
}

I am reading the value in another function which scan through this value after every second. If I comment out this line:

script_start_flag = testStruct.p_value[0];

Everything works fine. As soon as this line is un-commented (values is saved in local variable), and some value is sent from nRFConnect app, all services stop responding, the device comes into a sort of HALT condition. Very frustrating situation.

RE: Passing Characteristic data to Function

Aftab — Wed, 10 Apr 2019 15:01:42 GMT

Missing the data from NRF_LOG_INFO apart, when services stop responding? The device gets disconnected. I have also tried:

attr_md_1.rd_auth = 1;
attr_md_1.wr_auth = 1;

RE: Passing Characteristic data to Function

cbd — Wed, 10 Apr 2019 12:18:19 GMT

Are you relying totally on NRF_LOG_DEBUG output to determine whether you are handling the data?

I'm using SES for coding and have found that due to the SoftDevice's higher priority for BLE handling I'll often lose NRF_LOG_DEBUG data even though code is obviously running e.g. BLE data triggering formatted data on the UART.

On a side note I'd recommend that you declare global_flag volatile.