SAADC Example

[1730143]

Hi Nordic:

I have a question about retart saadc. i want to restart saadc in a bsp event(BSP_EVENT_KEY_3) and it works. the following is my code:

int spcr_flag = 0;
void bsp_event_handler(bsp_event_t event)
{
	switch (event)
	{
		case BSP_EVENT_KEY_3:
			if(opswitch)
			{
				spcr_flag = 1;
				stop_saadc();
				start_saadc();
			}			
			break;							
		default:
			break;
	}
}
void stop_saadc(void)
{
	nrf_drv_timer_disable(&m_timer);
	nrf_drv_timer_uninit(&m_timer);
	nrf_drv_ppi_channel_disable(m_ppi_channel);
	nrf_drv_ppi_uninit();
	nrf_drv_saadc_abort();
	nrf_drv_saadc_uninit();
	while(nrf_drv_saadc_is_busy());
}
void start_saadc(void)
{
	saadc_sampling_event_init();
	saadc_init();
	saadc_sampling_event_enable();
	m_adc_evt_counter= 0;
}

i learned in this forum that this stop_saadc function can solve the channel data shifting problem, but is it really neccessary with so many steps like that?

and how many times it takes to finish stop_saadc() and start_saadc() ? how could i measure it? i hope it is as short as possible.

i sampled 4 channels(ch0~ch3) with two buffers, the buffer size(SAMPLES_IN_BUFFER) is 4.

in my opinion, if the last sample is not finished when i restart saadc, there may be some residual data in p_buffer(for example, channel0 and channel1 data), and the next sample channel0 and channel1 data may store with them in the same buffer. in the end,the numbers of saadc data for each channel may be different. so i want to clear the p_buffer before restart saadc,i don't know how to ？ memset(p_event->data.done.p_buffer,'\0',4)？. i don't know if my understanding  is right.

[1730143]

Hi Nordic:

i found in this forum:

i use TASK_CAPTURE to measure time consume:

i enable TIMER2 in sdk_config.h

code:

nrf_drv_timer_config_t timer_cfg2 = NRF_DRV_TIMER_DEFAULT_CONFIG;
timer_cfg2.bit_width = NRF_TIMER_BIT_WIDTH_32;
timer_cfg2.mode = NRF_TIMER_MODE_TIMER;
err_code = nrf_drv_timer_init(&m_timer2, &timer_cfg2, timer_handler);
APP_ERROR_CHECK(err_code);

nrf_drv_timer_enable(&m_timer2);
NRF_TIMER2->TASKS_CAPTURE[1] = 1;
stop_saadc();
start_saadc();
counter = NRF_TIMER2->CC[1];
NRF_LOG_INFO("counter:%d",counter);

"counter" is always 8 , it is not right. what is right way to measure time?

thanks in advance!!

[Jared]

Hi,

i learned in this forum that this stop_saadc function can solve the channel data shifting problem,

Exactly which problem are you referring to? You only need to call nrf_drv_saadc_uninit to un-initialize the driver, alternatively you can also call nrf_drv_saadc_abort() to make sure that you're not un-initializing it in a middle of a conversion. See this case. Yes, you can use a timer for measuring elapsed time between function calls.

1730143 said:

"counter" is always 8 , it is not right. what is right way to measure time?

Do you mean by this that you always get 8 ticks between each time you reset the saadc?

regards

Jared 

[1730143]

NRF_TIMER2->TASKS_CAPTURE[1] = 1;
counter = NRF_TIMER2->CC[1];
NRF_LOG_INFO("counter:%d",counter);
stop_saadc();
start_saadc();
NRF_TIMER2->TASKS_CAPTURE[1] = 1;
counter = NRF_TIMER2->CC[1];
NRF_LOG_INFO("counter:%d",counter);

I learned that i should enable Capture task again and read the "counter" value,then subtract

thanks Jared

[Jared]

This would get you the time elapsed between the first call to the capture task to the second call. I'm not sure if you have a specific question or if you've solved the issue?

[1730143]

Thanks Jared,

i have solved this issue.