Allocating the SAADC to multiple DPPI channels

[Ted H]

Hi,

I would like to enable the SAADC to read multiple DPPI channels. I am using a timer to publish multiple channels and my code looks like this:

	NRF_TIMER1->PUBLISH_COMPARE[0] = DPPIC_SUBSCRIBE_CHG_EN_EN_Msk | dppi_channel_0;
	NRF_SAADC->SUBSCRIBE_SAMPLE = DPPIC_SUBSCRIBE_CHG_EN_EN_Msk | dppi_channel_0;

	NRF_TIMER1->PUBLISH_COMPARE[1] = DPPIC_SUBSCRIBE_CHG_EN_EN_Msk | dppi_channel_1;
	NRF_GPIOTE->SUBSCRIBE_SET[1] = DPPIC_SUBSCRIBE_CHG_EN_EN_Msk | dppi_channel_1;
	NRF_SAADC->SUBSCRIBE_SAMPLE = DPPIC_SUBSCRIBE_CHG_EN_EN_Msk | dppi_channel_1;

	NRF_TIMER1->PUBLISH_COMPARE[2] = DPPIC_SUBSCRIBE_CHG_EN_EN_Msk | dppi_channel_2;
	NRF_GPIOTE->SUBSCRIBE_CLR[1] = DPPIC_SUBSCRIBE_CHG_EN_EN_Msk | dppi_channel_2;
	NRF_SAADC->SUBSCRIBE_SAMPLE = DPPIC_SUBSCRIBE_CHG_EN_EN_Msk | dppi_channel_2;
	
	NRF_TIMER1->PUBLISH_COMPARE[3] = DPPIC_SUBSCRIBE_CHG_EN_EN_Msk | dppi_channel_3;
	NRF_GPIOTE->SUBSCRIBE_SET[2] = DPPIC_SUBSCRIBE_CHG_EN_EN_Msk | dppi_channel_3;
	NRF_SAADC->SUBSCRIBE_SAMPLE = DPPIC_SUBSCRIBE_CHG_EN_EN_Msk | dppi_channel_3;

	NRF_TIMER1->PUBLISH_COMPARE[4] = DPPIC_SUBSCRIBE_CHG_EN_EN_Msk | dppi_channel_4;
	NRF_GPIOTE->SUBSCRIBE_CLR[2] = DPPIC_SUBSCRIBE_CHG_EN_EN_Msk | dppi_channel_4;
	NRF_SAADC->SUBSCRIBE_SAMPLE = DPPIC_SUBSCRIBE_CHG_EN_EN_Msk | dppi_channel_4;

	NRF_TIMER1->PUBLISH_COMPARE[5] = DPPIC_SUBSCRIBE_CHG_EN_EN_Msk | dppi_channel_5;

However, the SAADC is only triggered at the last SAADC subscription call: NRF_SAADC->SUBSCRIBE_SAMPLE = DPPIC_SUBSCRIBE_CHG_EN_EN_Msk | dppi_channel_4. 

Is there any way that I can trigger multiple SAADC reads within the DPPI channels?

The timer1 is initialized with the following:

static void timer1_init(void)
{
	nrfx_err_t err = NRFX_SUCCESS;
	nrfx_timer_config_t timer_cfg = NRFX_TIMER_DEFAULT_CONFIG;
	timer_cfg.bit_width = NRF_TIMER_BIT_WIDTH_32;

	err = nrfx_timer_init(&timer1, &timer_cfg, timer1_evt_handler);
	if(err != NRFX_SUCCESS)
	{
		LOG_ERR("Error! Could not initialize TIMER1: %d\n", err);
	}

	nrfx_timer_extended_compare(&timer1, NRF_TIMER_CC_CHANNEL0, nrfx_timer_us_to_ticks(&timer1, 800), NRF_TIMER_SHORT_COMPARE0_CLEAR_MASK, false);
	nrfx_timer_extended_compare(&timer1, NRF_TIMER_CC_CHANNEL1, nrfx_timer_us_to_ticks(&timer1, 100), NRF_TIMER_SHORT_COMPARE0_CLEAR_MASK, false);
	nrfx_timer_extended_compare(&timer1, NRF_TIMER_CC_CHANNEL2, nrfx_timer_us_to_ticks(&timer1, 200), NRF_TIMER_SHORT_COMPARE0_CLEAR_MASK, false);
	nrfx_timer_extended_compare(&timer1, NRF_TIMER_CC_CHANNEL3, nrfx_timer_us_to_ticks(&timer1, 300), NRF_TIMER_SHORT_COMPARE0_CLEAR_MASK, false);
	nrfx_timer_extended_compare(&timer1, NRF_TIMER_CC_CHANNEL4, nrfx_timer_us_to_ticks(&timer1, 400), NRF_TIMER_SHORT_COMPARE0_CLEAR_MASK, false);
	nrfx_timer_extended_compare(&timer1, NRF_TIMER_CC_CHANNEL5, nrfx_timer_us_to_ticks(&timer1, 1000), NRF_TIMER_SHORT_COMPARE0_CLEAR_MASK, false);
}

Thanks!

Ted

[Øivind]

Hi,

I'll try to implement this and get back to you. Which SDK version are you using?

[Ted H]

I am using nRF Connect SDK v1.7.1 with SES.

[Øivind]

Please read the section of the DPPI documentation titled "Subscribing to and publishing on channels".
https://infocenter.nordicsemi.com/index.jsp?topic=%2Fps_nrf5340%2Fdppi.html&cp=3_0_0_6_8

"one task can be triggered by multiple events by publishing different events to the same channel."
You need to set all the events that you want to trigger the SAADC sampling task to the same channel, and have the task subscribe to that channel.

[Ted H]

Thanks, for the info from the documentation. I read it through but it confuses me even more now...

So it is "not possible" to trigger the SAADC in multiple channels, right? Currently, if I change the configuration to the following, it works but this is not the right setup for my application:

	NRF_TIMER1->PUBLISH_COMPARE[1] = DPPIC_SUBSCRIBE_CHG_EN_EN_Msk | dppi_channel_1;
	NRF_GPIOTE->SUBSCRIBE_OUT[1] = DPPIC_SUBSCRIBE_CHG_EN_EN_Msk | dppi_channel_1;
	NRF_GPIOTE->SUBSCRIBE_OUT[2] = DPPIC_SUBSCRIBE_CHG_EN_EN_Msk | dppi_channel_1;
	NRF_GPIOTE->SUBSCRIBE_OUT[3] = DPPIC_SUBSCRIBE_CHG_EN_EN_Msk | dppi_channel_1;
	NRF_GPIOTE->SUBSCRIBE_OUT[4] = DPPIC_SUBSCRIBE_CHG_EN_EN_Msk | dppi_channel_1;
	NRF_SAADC->SUBSCRIBE_SAMPLE = DPPIC_SUBSCRIBE_CHG_EN_EN_Msk | dppi_channel_1;

What I want to do is the SAADC is triggered for each published channel. Is it a feasible feature in DPPI?

[Øivind]

Sounds like it might be too complex for the dppi, but to be sure, can you explain the application in a bit more detail? What's the behavior you are looking for?