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]

You are able to get the GPIOs to work like you want, correct? If you ignore the SAADC?

[Ted H]

Correct, the GPIOTE pins are working as expected!

[Øivind]

Ok, great! Then I believe you will get basically what you want if you make the EGU subscribe to all the channels on different tasks, then publish all the EGU events to the same channel, which triggers the SAADC_SAMPLE.

https://infocenter.nordicsemi.com/index.jsp?topic=%2Fps_nrf5340%2Fegu.html&cp=3_0_0_6_10

[Ted H]

Please confirm if my understanding is correct:

1. Keep the current GPIOTE subscriptions to the timer1
2. Subscribe the EGU to all GPIOTE-subscribed channels (i.e. timer1 for my case)
3. Create the EGU event for the SAADC

I can't find a suitable example utilizing the EGU on nRF5340. Can you direct me to an applicable EGU sample code?

Thank you!

[Øivind]

Yes, so if you want SUBSCRIBE_SAMPLE to be triggered by channel 0-3, you instead trigger SUBSCRIBE_TRIGGER[0-3] in the EGU, one on each channel.
The EGU will then publish PUBLISH_TRIGGERED[0-3], which can all be set to channel 4.
Now, if you trigger SUBSCRIBE_SAMPLE on channel 4, you should get your desired behavior.

We don't have many samples which use the EGU, unfortunately.

nrf/samples/tfm/tfm_secure_peripheral
nrf/samples/bluetooth/radio_coex_3wire

use the EGU, but not in the same way that you are going to it seems.