Can't stop SAADC

[Alaa]

Hi,

When I try to stop ADC sampling, the adc driver keeps on busy. The function nrf_drv_saadc_is_busy() keeps returning true.

I looked in other posts (like this one) and found that this is the way to start and stop ADC:

void start_adc()
{
    saadc_sampling_event_init();
    saadc_init();
    saadc_sampling_event_enable();
}

void stop_adc()
{
	nrf_drv_timer_disable(&m_timer);
	nrf_drv_ppi_channel_disable(m_ppi_channel);
	while(nrf_drv_saadc_is_busy()); //--> always true
	nrf_drv_saadc_uninit();
}

But this is not working because while(nrf_drv_saadc_is_busy()); keeps returning true.

I'm using SDK 14 with double buffer and ble communication.

I read also this post and understood that it might be because of the double buffer. So I tried disabling it by:

1. Changing static nrf_saadc_value_t m_buffer_pool[2][SAADC_SAMPLES_IN_BUFFER] to static nrf_saadc_value_t m_buffer_pool[1][SAADC_SAMPLES_IN_BUFFER]

2. Deleting the following from saadc_init():

err_code = nrf_drv_saadc_buffer_convert(m_buffer_pool[1],SAADC_SAMPLES_IN_BUFFER);
APP_ERROR_CHECK(err_code);

and left only with:

    err_code = nrf_drv_saadc_buffer_convert(m_buffer_pool[0],SAADC_SAMPLES_IN_BUFFER);
    APP_ERROR_CHECK(err_code);

Am I doing this correctly?

Thanks!

[Jørgen Holmefjord]

Hi,

The SAADC driver will always be in the busy state when a buffer is setup for conversion (by calling nrf_drv_saadc_buffer_convert). It will not help to only disable double buffering, you also need to remove the second buffer.

You have two alternatives:

1. Call nrf_drv_saadc_abort to remove the buffers and stop any ongoing sampling. This will trigger the STOP task and put the driver in IDLE state when STOPPED event is received.
2. Disable double buffering, as you describe above, and only call stop_adc in your SAADC event handler when you receive a DONE event, but before you call nrf_drv_saadc_buffer_convert to setup the buffer for conversion again.

Best regards,
Jørgen

[Alaa]

Hi Jorgen,

Thanks for the reply.

I prefer to keep the double buffer so I tried the abort method. Calling nrf_drv_saadc_abort() alone doesn't stop the adc callback. It keeps triggering with constant value 1024. And then if I call my function start_system() again, I get a hard fault from nrf_drv_ppi_init() (133 error).

I also tried calling nrf_drv_saadc_uninit() after aborting - this did stop the callback, but I got the same hard fault (133)

[Jørgen Holmefjord]

nrf_drv_saadc_abort should stop the SAADC and any ongoing conversions, but if you are setting up new buffers and triggering sampling, you will still get callbacks. You should check the error codes from nrf_drv_timer_disable and nrf_drv_ppi_channel_disablein stop_adc, to make sure the sampling is actually stopped, before aborting and uninitializing the SAADC.

Error 133 (0x0085) means NRF_ERROR_MODULE_ALREADY_INITIALIZED. If do not uninit the PPI driver, it would be expected that you get this error when calling nrf_drv_ppi_init.

[Alaa]

Sorry I'm confused. Can you please tell me what's the proper way and the right order of operations to stop and restart ADC?

Thank you very much

[Jørgen Holmefjord]

This should be sufficient:

• Stop anything triggering the sample task (timer, PPI, etc.).
• Call nrf_drv_saadc_abort().
• Call nrf_drv_saadc_uninit().
• Call you SAADC+channels init function.
• Start whatever triggers sample task.