NRF54L15 adc channel does not get proper value with matter stack code

[Pratik Panchal]

Hello Nordic team,

For the (POC), I configured ADC channel 1 and interfaced a potentiometer to pin P1.14. The ADC was set up accordingly to read raw value from the potentiometer.

/ {
	zephyr,user {
		io-channels = <&adc 1>;
	};
};


&adc {
	#address-cells = <1>;
	#size-cells = <0>;

	channel@1 {
		reg = <1>;
		zephyr,gain = "ADC_GAIN_1";
		zephyr,reference = "ADC_REF_INTERNAL";
		zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;
		zephyr,input-positive = <NRF_SAADC_AIN7>; // P1.14
		zephyr,resolution = <12>;
		zephyr,oversampling = <2>; // Enable oversampling with a factor of 2
	};

};

As per "Exercise 1 – Interfacing with ADC using Zephyr API", we configured and initialized the ADC, and invoked it within the main() function.
We also included a function call to read the ADC value, as shown in the following code snippet:

//adc.cpp

int32_t readValue(void)
{
    int err;
    err = adc_read_dt(&smoke_adc, &smoke_seq);
    if (err < 0) {
        LOG_ERR("Smoke ADC read failed (%d)", err);
        return err;
    }

    LOG_INF("Smoke rawvalue : %d\n",smoke_buf);
}

To analyze the ADC reading values, we observed two scenarios:

1) As mentioned in the code below, when we called the readValue() function within the while(1) loop in main.cpp.

//main.cpp

int_main()
{
	if(smoke_init())
	{
		LOG_ERR("Smoke init failed");	
	}

	while(1)
	{
	    readValue();
		k_msleep(1000);
	}
	
	commenting StartApp function 
	
	CHIP_ERROR err = AppTask::Instance().StartApp();

	LOG_ERR("Exited with code %" CHIP_ERROR_FORMAT, err.Format());
	return err == CHIP_NO_ERROR ? EXIT_SUCCESS : EXIT_FAILURE;
}

2) The readVoltage() function is called every second using a timer, which is initialized through the SensorTimerHandler in the Apptask:Init() function. This function also initializes the Matter stack.
 

CHIP_ERROR AppTask::Init()
{
	/* Initialize Matter stack */
	ReturnErrorOnFailure(Nrf::Matter::PrepareServer());

	if (!Nrf::GetBoard().Init(ButtonEventHandler)) {
		LOG_ERR("User interface initialization failed.");
		return CHIP_ERROR_INCORRECT_STATE;
	}

	k_timer_init(&mSelfTestLedTimer, &SelfTestLedTimerTimeoutCallback, nullptr);
	k_timer_init(&mSelfTestTimer, &SelfTestTimerTimeoutCallback, nullptr);

	/* Register Matter event handler that controls the connectivity status LED based on the captured Matter network
	 * state. */
	ReturnErrorOnFailure(Nrf::Matter::RegisterEventHandler(Nrf::Board::DefaultMatterEventHandler, 0));

	/* Register Smoke CO Alarm test event triggers */
#ifdef CONFIG_NCS_SAMPLE_MATTER_TEST_EVENT_TRIGGERS
	/* Register Smoke CO alarm test events handler */
	static chip::SmokeCOTestEventTriggerHandler sSmokeCoAlarmTestEventTrigger;
	ReturnErrorOnFailure(Nrf::Matter::TestEventTrigger::Instance().RegisterTestEventTriggerHandler(
		&sSmokeCoAlarmTestEventTrigger));

	/* Register test event handler to change the power source. */
	ReturnErrorOnFailure(Nrf::Matter::TestEventTrigger::Instance().RegisterTestEventTrigger(
		kPowerSourceOnEventTriggerId,
		Nrf::Matter::TestEventTrigger::EventTrigger{ 0xFFFF, PowerSourceOnEventCallback }));
	ReturnErrorOnFailure(Nrf::Matter::TestEventTrigger::Instance().RegisterTestEventTrigger(
		kPowerSourceOffEventTriggerId,
		Nrf::Matter::TestEventTrigger::EventTrigger{ 0xFFFF, PowerSourceOffEventCallback }));
#endif
    // Read ADC value using Timer
	k_timer_init(&sSensorTimer, &SensorTimerHandler, nullptr);
	k_timer_user_data_set(&sSensorTimer, this);
	SensorActivateHandler(); 
	return Nrf::Matter::StartServer();
}

CHIP_ERROR AppTask::StartApp()
{
	ReturnErrorOnFailure(Init());

	while (true) {
		Nrf::DispatchNextTask();
	}

	return CHIP_NO_ERROR;
}

Based on the above two code snippets, we will examine adc raw data values based on following two scenarios:

A) Without initializing the Matter stack, where the value is read within the while(1) loop in main.cpp.
B) With the Matter stack initialized, where the value is read using a timer.

• Scenario A-1 readings:
  
  
  
• Scenario B-1 readings:
  
  
  
• Scenario A-2 readings:
  
  
  
• Scenario B-2 readings:
  
  
  In above we can see the two scenarios reading,
  where mentioned A/B defined scenario (as mentioned above) and 1/2 defined reading number. 
  
  

• Scenario A-1: With the potentiometer set to a specific value, we observed a reading of ~1111.

• Scenario B-1: With the same potentiometer setting, we observed a reading of 4092.

• Scenario A-2: At another potentiometer setting, the reading was ~241.

• Scenario B-2: With the same potentiometer setting, the reading was around 26xx.

  we can see the clear difference in both scenarios.
  
  we want to understand why we got a wrong reading when we initialize matter stack ?
  
  Looking forward to your insights.
  
  Thanks & Regards,
  
  Pratik Panchal