Send BLE data from saadc_callback

[StephaneJ]

Hi,

There is something I don't understand and I request your help to answer my interrogation. What I want to do is a SAADC conversion then send the result of this conversion over BLE.

So basically my first working version looks something like (simplified for readability) :

#define SAMPLES_IN_BUFFER 1
static nrf_saadc_value_t m_buffer[SAMPLES_IN_BUFFER];
static int16_t value_to_send = 0;


void send_value()
{
    ble_custom_on_sensor_change(m_conn_handle, &m_ble, value_to_send);    // Same as ble_lbs_on_button_change
    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);
    }
}


void saadc_callback(nrf_drv_saadc_evt_t const * p_event)
{
    if (p_event->type == NRF_DRV_SAADC_EVT_DONE)
    {
        nrf_drv_saadc_buffer_convert(p_event->data.done.p_buffer, SAMPLES_IN_BUFFER);

        /* Send the value */
        value_to_send = p_event->data.done.p_buffer[0];
    }
}

void saadc_init(void)
{
...
}


int main(void)
{
    ...

    saadc_init();

    // Enter main loop.
    for (;;)
    {
        nrf_delay_ms(500);
        nrf_drv_saadc_sample();
        send_value();

        if (NRF_LOG_PROCESS() == false)
        {
            power_manage();
        }
    }
}

But with this version, I am afraid that send_value() could be called before nrf_drv_saadc_sample() has updated the value_to_send.

So now I want to call the function send_value() within the saadc_callback but it doesn't work and I can't find a way to Debug it. It looks like it failed during the sd_ble_gatts_hvx() call (from the ble_lbs_on_button_change function (or ble_custom_on_sensor_change in my case).

So basically, this doesn't work, doesn't even succeed to establish a connection in BLE :

#define SAMPLES_IN_BUFFER 1
static nrf_saadc_value_t m_buffer[SAMPLES_IN_BUFFER];


void saadc_callback(nrf_drv_saadc_evt_t const * p_event)
{
    if (p_event->type == NRF_DRV_SAADC_EVT_DONE)
    {
        nrf_drv_saadc_buffer_convert(p_event->data.done.p_buffer, SAMPLES_IN_BUFFER);

        /* Send the value */
        ble_custom_on_sensor_change(m_conn_handle, &m_ble, p_event->data.done.p_buffer[0]);    // Same as ble_lbs_on_button_change
        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);
        }
    }
}

void saadc_init(void)
{
...
}


int main(void)
{
    ...

    saadc_init();

    // Enter main loop.
    for (;;)
    {
        nrf_delay_ms(500);
        nrf_drv_saadc_sample();

        if (NRF_LOG_PROCESS() == false)
        {
            power_manage();
        }
    }
}

Any idea why ?

Thanks

[Vidar Berg]

Hi,

sd_ APIs can only be called from main context, or from interrupt context with lower priority than '4':

"SoftDevice API functions can only be called from a lower interrupt priority level (higher numerical value for the priority level) than the SVC priority. For more information, see Interrupt priority levels."

Could this be the problem? Suggest to set the SAADC interrupt priority to '7', which is the lowest possible priority, and see if you get the same result. 

[liu_zhixiang]

Hi ,StephaneJ Do you solve this question.I meet the same one with you.

[StephaneJ]

Yes thanks to the answer from Vidar Berg. It was a priority issue. 

[liu_zhixiang]

I have set  the SAADC interrupt priority to '7'.Can you help me see this link:https://devzone.nordicsemi.com/f/nordic-q-a/36246/saadc-sample-cant-use-with-sd_power_system_off