NRF54L15-DK : ADC Threshold Event Configuration using LPCOMP and ANADETECT

[Pratik Panchal]

Hello Nordic Team,

I am currently working with the NRF54L15-DK. I have successfully configured the simple ADC on AIN4 (P1.11) and am able to read the raw sensor values.

Overlay : 

&adc {
	#address-cells = <1>;
	#size-cells = <0>;
	
	channel@4 {
		reg = <4>;
		zephyr,gain = "ADC_GAIN_1"; //"ADC_GAIN_1_4"
		zephyr,reference = "ADC_REF_INTERNAL";
		zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;
		zephyr,input-positive = <NRF_SAADC_AIN4>; /* P1.11 */
		zephyr,resolution = <12>;
		//zephyr,oversampling = <2>;
	};
};

However, I would like to understand how to configure and set an ADC threshold using the ANADETECT feature. Specifically, I want to know how to detect when the ADC value crosses a defined threshold, either up , down or cross  and how to receive an event when this occurs. Additionally, I would like guidance on configuring the LPCOMP for this purpose.

Please provide the necessary prj.conf settings, .overlay configuration, and a sample example to help me implement this functionality.

Thanks & Regards,
Pratik Panchal

[Kenneth]

Hi,

I suggest to check out this answer:  Using the new LPCOMP driver in Zephyr 

Kenneth 

[Pratik Panchal]

Hello Kenneth 

Thank you for your response.

I reviewed the Nordic thread you shared and used the referenced code to configure and integrate a comparator into my application. I connected a potentiometer to the defined ADC pin for input variation.

However, I expected to receive specific up or down events based on the configured threshold up/down values.
I referred to the overlay file from the provided GitHub repository, but despite defining th_up and th_down values, the test_callback function does not increment the count on defined up or down threshold, but it only increments when we fully increase the potentiometer value to 4092 = 0.899V, and the event 
bool event = comparator_get_output(test_dev); Returns 1 on 0.899V.

Even I modified the value of th-up to 40, then also the event returns 1 only at 0.899V.

Here, my application overlay for the comparator :

&comp {
	compatible = "nordic,nrf-comp";
	main-mode = "SE";
	psel = "AIN4"; /* P1.11 */
	refsel = "VDD";
	sp-mode = "HIGH";
	th-up = <63>;
	th-down = <31>;//<59>;
	isource = "DISABLED";
	status = "okay";
};

 

Could you please provide a sample that demonstrates the detailed usage of the APIs for configuring up/down thresholds and handling the corresponding events?

Thanks & Regards,
Pratik Panchal

[Kenneth]

Hi,

Dont' have time to test the code, but make sure you understand the difference between COMP and LPCOMP:
https://docs.nordicsemi.com/bundle/ps_nrf54L15/page/comp.html 
https://docs.nordicsemi.com/bundle/ps_nrf54L15/page/lpcomp.html 

One can be used in sleep and wakeup the chip (lpcomp), the other is only active while the CPU is running (comp).

Kenneth

[Pratik Panchal]

Hi Kenneth,

Thank you for your response.

I have reviewed the documents you provided and, based on that, I have defined the comparator.

The comparator configuration is provided below in the overlay.

.Overlay

&comp {
	compatible = "nordic,nrf-comp";
	main-mode = "SE";
	psel = "AIN4"; /* P1.11 */
	refsel = "VDD";
	sp-mode = "HIGH";
	th-up = <63>;
	th-down = <31>;//<59>;
	isource = "DISABLED";
	enable-hyst;
	status = "okay";
};

and define the init_comparator() function and the IRQ interrupt. When the threshold is crossed (either upward or downward), the function comp_event_handler() should be invoked.

Code:

//comparator node
static const struct device *test_dev = DEVICE_DT_GET(DT_ALIAS(test_comp));

bool event_flag = true;  //<----------- this flag needed because sometime when we adc fall from up to down then both event triggered down and up

void comp_event_handler(void)
{
   if (NRF_COMP->EVENTS_UP) {
		if(!event_flag)
		{
			printk("\tEVENTS_UP >>>>>> : [%d]\n", NRF_COMP->EVENTS_UP);
        	NRF_COMP->EVENTS_UP = 0;
			NRF_COMP->EVENTS_DOWN = 0;
			event_flag = true;
		}
    }

	if (NRF_COMP->EVENTS_DOWN)
	{
		if (event_flag)
		{
			printk("\tEVENTS_DOWN <<<<<< : [%d]\n", NRF_COMP->EVENTS_DOWN);
			NRF_COMP->EVENTS_DOWN = 0;
			NRF_COMP->EVENTS_UP = 0;
			event_flag = false;
		}
	}

int init_comparator()
{
struct comp_nrf_comp_se_config comp_config = {
		.psel = COMP_NRF_COMP_PSEL_AIN4,
		.sp_mode = COMP_NRF_COMP_SP_MODE_HIGH,
		.isource = COMP_NRF_COMP_ISOURCE_DISABLED,
		.refsel = COMP_NRF_COMP_REFSEL_VDD,
		.th_down = 5, //<---- up threshold  
		.th_up = 16, // <----- down threshold
	};
	comp_nrf_comp_configure_se(test_dev, &comp_config);
	
	// Configure event UP to publish
	NRF_COMP->PUBLISH_UP = COMP_PUBLISH_UP_EN_Enabled;

	// Define handler for event UP
	NRF_COMP->INTENSET = COMP_INTENSET_UP_Msk;

	// Check if the IRQ is already registered before connecting
	if (!irq_is_enabled(DT_IRQN(DT_NODELABEL(comp)))) {
		// Register the interrupt handler
		IRQ_CONNECT(DT_IRQN(DT_NODELABEL(comp)), DT_IRQ(DT_NODELABEL(comp), priority), comp_event_handler, NULL, 0);

		// Enable the interrupt
		irq_enable(DT_IRQN(DT_NODELABEL(comp)));
	} else {
		printk("IRQ %d is already registered.\n", DT_IRQN(DT_NODELABEL(comp)));
	}
	
		// Enable and start COMP
	NRF_COMP->ENABLE = 2;
	NRF_COMP->TASKS_START = 1;
}

Proj.conf

# Comparator
CONFIG_COMPARATOR=y
CONFIG_NRFX_COMP=y
CONFIG_SHARED_INTERRUPTS=y

According to the formula provided in the documentation for the TH threshold registers.

VDOWN = (THDOWN+1)/64*VREF
VUP = (THUP+1)/64*VREF

For example, with a threshold of 5, the expected voltage is 104 mV based on the given formula.

e.g, Threshold =  5   
       Voltage(mv)  = 104
     
I expected mv value as per the above formula, but it is not.

However, in my testing, I observed:

e.g, Threshold =  5   
       Voltage(mv)  = 168.75

After reverse engineering, I found that the voltage calculation in the system follows this formula:

V = ((TH + 1)/32) * Vref  // divided by 32 not 64

Please find attached the log table in .txt.  

Could you please clarify what changes or settings are required to achieve the voltage readings as per the formula provided in the documentation?

Thanks & Regards,
Pratik

Fullscreen th_adc_tab.txt Download

Formula : V = ((TH + 1)/32) * Vref
Where Vref = 0.9V

Threshold |       Voltage (mV)      |   ADC Raw
-------------------------------------------------
    0     |          28.12          |        128       
    1     |          56.25          |        256       
    2     |          84.38          |        384       
    3     |          112.50         |        512       
    4     |          140.62         |        640       
    5     |          168.75         |        768       
    6     |          196.88         |        896       
    7     |          225.00         |       1024       
    8     |          253.12         |       1152       
    9     |          281.25         |       1280       
   10     |          309.38         |       1408       
   11     |          337.50         |       1536       
   12     |          365.62         |       1664       
   13     |          393.75         |       1792       
   14     |          421.88         |       1920       
   15     |          450.00         |       2048       
   16     |          478.12         |       2176       
   17     |          506.25         |       2304       
   18     |          534.38         |       2432       
   19     |          562.50         |       2560       
   20     |          590.62         |       2688       
   21     |          618.75         |       2816       
   22     |          646.88         |       2944       
   23     |          675.00         |       3072       
   24     |          703.12         |       3200       
   25     |          731.25         |       3328       
   26     |          759.38         |       3456       
   27     |          787.50         |       3584       
   28     |          815.62         |       3712       
   29     |          843.75         |       3840       
   30     |          871.88         |       3968       
   31     |          900.00         |       4096       
   32     |          928.12         |       4224       
   33     |          956.25         |       4352       
   34     |          984.38         |       4480       
   35     |         1012.50         |       4608       
   36     |         1040.62         |       4736       
   37     |         1068.75         |       4864       
   38     |         1096.88         |       4992       
   39     |         1125.00         |       5120       
								  

[Pratik Panchal]

Hello Kenneth,

Just a quick reminder—have there been any updates or findings regarding my query?

Thanks & Regards,
Pratik

[Pratik Panchal]

Hello Nordic Team,

Could you please answer my query?

Regards,
Pratik