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Exercise 1 – Measuring sleep current with different GPIO interrupt types

This exercise examines how the interrupt type affects sleep current (System ON IDLE) using both the pure PORT sense and the GPIOTE EVENT IN mechanisms.

This is demonstrated by configuring an interrupt on button0 on the nRF54L15 DK. First, the interrupt uses the GPIOTE EVENT IN, and you measure the device’s System ON IDLE. As discussed in the GPIO interrupt types on the nRF54L Series topic, this will keep the associated power domain powered, resulting in higher sleep current, which you measure using the PPK2. Then you switch off the GPIOTE EVENT IN and use a pure PORT sense mechanism, measuring the sleep current using the PPK2. You will notice that the sleep current is much lower now, as the associated power domain is no longer running.

Button0 on the nRF54L15 DK is an active-low button connected to GPIO P1, pin 13 (P1.13); hence, the PIN will be configured through the board files to be pulled up to VDD.

The high-level GPIO API in nRF Connect SDK/Zephyr is used for this. It is also possible to use the low-level nrfx drivers to achieve the same functionality.

Exercise steps

In the GitHub repository for this course, go to the base code for this exercise, found in l6/l6_e1.

1. Examine the code base of the exercise.

This code configures a button connected to P1.13 with an edge-triggered interrupt that fires when the button is pressed. When the interrupt occurs, the callback function toggles an LED.

	ret = gpio_pin_interrupt_configure_dt(&button, GPIO_INT_EDGE_TO_ACTIVE);
	if (ret != 0) {
		printk("Error %d: failed to configure interrupt on %s pin %d\n", ret, button.port->name, button.pin);
		return 0;
	}

C++

GPIO_INT_EDGE_TO_ACTIVE configures an interrupt that triggers when the pin transitions to its active state.

The nRF54L15 DK button0 is defined as follows:

gpios = <&gpio1 13 (GPIO_PULL_UP | GPIO_ACTIVE_LOW)>;

C++

When the button0 is not pressed → Pin is HIGH (pulled up), button0 pressed → Pin goes LOW (active)

GPIO_INT_EDGE_TO_ACTIVE = falling edge = fires when button0 is pressed

The question you need to answer now is whether the falling edge detection of the code is going to be implemented using GPIOTE EVENT IN or pure PORT sense. Since the low-level nrfx drivers are not used directly, you need to dig a bit deeper to find out.

Note

The GPIO API does not include debouncing. If you are looking into an implementation of button events with debouncing, check out the input subsystem in the nRF Connect SDK/Zephyr.

2. Start measuring the power consumption.

Run the Power Profiler application and ensure the DK is powered over the PPK2, as we have done in previous exercises.

3. Build the code and flash it to your DK.

4. Examine the sleep current of the device.

Ideally, this should be System ON IDLE current (~3 µA on the nRF54L15 SoC full-memory retention). However, you will see that the sleep current is way more than that – it is ~20 µA!

Important

The 17 µA difference (20-3) will differ between SoCs within the nRF54L Series (for example, nRF54LM20 vs nRF54L15) due to different die sizes.

Since an edge detection (GPIO_INT_EDGE_TO_ACTIVE) was requested in the application code, without explicitly specifying a sense-edge-mask, the driver will allocate a GPIOTE IN event for the pin by default. This means that the associated power domain (in the case of the nRF54L15 DK, that will be the PERI) will be kept powered during System ON IDLE, and hence, the high unexpected System ON IDLE current of ~20 µA instead of ~3 µA.

5. Examine what is happening at the register level.

You can verify this using an nRF Connect debug session and the peripheral viewer.

5.1 Set a breakpoint on the printk("Press the button\n");.

More on this: See Debugging in nRF Connect for VS Code in the nRF Connect SDK Intermediate course for more information on how to do this.

5.2 Start a debug session in nRF Connect for VS Code by clicking Debug in the ACTIONS view.

Note

Ignore the warning “Debug option not enabled” and click Debug anyway. The Kconfig selections in the prj.conf file are CONFIG_DEBUG_OPTIMIZATIONS=y and CONFIG_DEBUG_THREAD_INFO=y.

5.3. Make sure to set the Breakpoint at the line printk(“Press the button”).

5.4 Click Continue

Execution should stop at the breakpoint:

5.5 Examine the GPIOTE associated with GPIO P1.

Examine the GPIOTE associated with GPIO P1, which is GPIOTE20 (for the nRF54L15 DK) as covered in the GPIO interrupt types on the nRF54L Series topic

Note

Different nRF54L Series DKs might have different pin assignments for Button0. Check the table below:

nRF54L15 DK	nRF54LM20 DK	nRF54LS05 DK	nRF54LV10A DK
Button0	P1.13	P1.26	P1.13	P1.21
Associated GPIOTE	GPIOTE20	GPIOTE20	GPIOTE20	GPIOTE20
GPIO Port	P1	P1	P1	P1
sense-edge-mask for Button0	<(1 << 13)>	<(1 << 26)>	<(1 << 13)>	<(1 << 21)>

You can see that the GPIOTE IN channel is allocated to pin 0xD (13), port 0x1 (1), on a polarity of HiToLo (falling edge). This is the suspected reason for the high power consumption of ~ 20 µA in System ON IDLE.

Important

Close the debug session after verifying the register content because the SWD interface draws high current during debugging, which prevents accurate System ON IDLE measurements.

6. Disable the GPIOTE IN event.

This is a straightforward operation in the nRF Connect SDK by setting the associated sense-edge-mask bit mask (pin 13) in the board overlay file for the associated port (port 1).

Uncomment the line in the corresponding DK board overlay file:

&gpio1 {
   /* STEP 6 - Disable the GPIOTE IN event on pin 13 (button 0) */
 sense-edge-mask = <(1 << 13)>;
};

Copy

&gpio1 {
   /* STEP 6 - Disable the GPIOTE IN event on pin 13 (button 0) */
 sense-edge-mask = <(1 << 13)>;
};

Devicetree

&gpio1 {
   /* STEP 6 - Disable the GPIOTE IN event on pin 26 (button 0) */
 sense-edge-mask = <(1 << 26)>;
};

Copy

&gpio1 {
   /* STEP 6 - Disable the GPIOTE IN event on pin 26 (button 0) */
 sense-edge-mask = <(1 << 26)>;
};

Devicetree

&gpio1 {
   /* STEP 6 - Disable the GPIOTE IN event on pin 13 (button 0) */
 sense-edge-mask = <(1 << 13)>;
};

Copy

&gpio1 {
   /* STEP 6 - Disable the GPIOTE IN event on pin 13 (button 0) */
 sense-edge-mask = <(1 << 13)>;
};

Devicetree

&gpio1 {
   /* STEP 6 - Disable the GPIOTE IN event on pin 21 (button 0) */
 sense-edge-mask = <(1 << 21)>;
};

Copy

&gpio1 {
   /* STEP 6 - Disable the GPIOTE IN event on pin 21 (button 0) */
 sense-edge-mask = <(1 << 21)>;
};

Devicetree

With this mask, you no longer allocate a GPIOTE channel. A pure PORT sense mechanism (+ LATCH edge detection) is used instead. This will save a lot of power in System ON IDLE, as the associated power domain (PERI for the nRF54L15 DK) is no longer powered during System ON IDLE, and is accurate enough for actions like button presses and sensor interrupts.

7. Pristine build the application and flash it to your DK.

8. Examine the sleep current of the device using the Power Profiler.

It should now be the normal “expected”, System ON IDLE current of ~ 3 µA. Savings of 10x compared to the GPIOTE IN event.

9. (Optional) If you redo step 5, you should see that there is no channel used in GPIOTE20.

The PORT sense is used in GPIO P1.13 (or the matching GPIO in case of DK different than nRF54L15DK ) .

10. (Optional) Evaluate the behavior when using the LEVEL detention in nRF Connect SDK.

Is it going to use GPIOTE EVENT IN ?

ret = gpio_pin_interrupt_configure_dt(&button,
					      GPIO_INT_LEVEL_ACTIVE);

C++

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Exercise 1 – Measuring sleep current with different GPIO interrupt types

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