drivers: misc: Add Low-voltage detection (LVD) driver support for RX130

[quytranpzz]

Introduce low-voltage detection driver support on RX130
The voltage detection circuit (LVD) monitors the voltage level input to the VCC or external pin using a program.
Upon detecting a voltage level transition (either upward or downward) past the configured threshold, the system can generate a reset or an interrupt, enabling appropriate protective or recovery actions.

[github-actions]

The following west manifest projects have changed revision in this Pull Request:

Name	Old Revision	New Revision	Diff
hal_renesas	zephyrproject-rtos/hal_renesas@0cdd997	zephyrproject-rtos/hal_renesas@f728bb5 (main)	zephyrproject-rtos/[email protected]

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[thenguyenyf]

LGTM

[kartben]

It looks to me as if it should be using the Comparator API instead of being a misc. driver but I will let @bjarki-andreasen chime in.

[kartben]

-1 until the comparator discussion happens. I will also add comments re: a few things that need fixing in the docs and sample. Thanks!

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[bjarki-andreasen]

This hardware maps really well to the comparator subsystem, check out https://docs.zephyrproject.org/latest/hardware/peripherals/comparator.html , and see the comments I added to this PR. The comparator subsystem comes with documentation, a shell, and test suites, so you get a lot "for free" including portability using it instead of introducing a new API :)

There is a component in tree which contains multiple comparator's as well, check out https://github.com/zephyrproject-rtos/zephyr/blob/main/dts/bindings/comparator/renesas%2Cra-acmphs-global.yaml and https://github.com/zephyrproject-rtos/zephyr/blob/main/dts/bindings/comparator/renesas%2Cra-acmphs.yaml Comparators don't have "channels", a comparator is "a comparator" if there are two channels, there are two comparators :)

[bjarki-andreasen]

This maps well to

zephyr/include/zephyr/drivers/comparator.h

Lines 60 to 74 in 90723c8

	/**
	* @brief Get comparator's output state
	*
	* @param dev Comparator device
	*
	* @retval 1 Output state is high
	* @retval 0 Output state is low
	* @retval -errno code Failure
	*/
	__syscall int comparator_get_output(const struct device *dev);
	static inline int z_impl_comparator_get_output(const struct device *dev)
	{
	return DEVICE_API_GET(comparator, dev)->get_output(dev);
	}

[bjarki-andreasen]

This maps to

zephyr/include/zephyr/drivers/comparator.h

Lines 27 to 36 in 90723c8

	enum comparator_trigger {
	/** No trigger */
	COMPARATOR_TRIGGER_NONE = 0,
	/** Trigger on rising edge of comparator output */
	COMPARATOR_TRIGGER_RISING_EDGE,
	/** Trigger on falling edge of comparator output */
	COMPARATOR_TRIGGER_FALLING_EDGE,
	/** Trigger on both edges of comparator output */
	COMPARATOR_TRIGGER_BOTH_EDGES
	};

specifically

zephyr/include/zephyr/drivers/comparator.h

Line 31 in 90723c8

COMPARATOR_TRIGGER_RISING_EDGE,

which seems to be the only edge this hardware supports

[bjarki-andreasen]

These map to

zephyr/include/zephyr/drivers/comparator.h

Lines 51 to 56 in 90723c8

	__subsystem struct comparator_driver_api {
	comparator_api_get_output get_output;
	comparator_api_set_trigger set_trigger;
	comparator_api_set_trigger_callback set_trigger_callback;
	comparator_api_trigger_is_pending trigger_is_pending;
	};

get_status -> get_output, callback_set -> set_trigger_callback, clear_status -> trigger_is_pending. The comparator API additionally has the set_trigger API which allows the user to enable/disable the edge detection (interrupt), and details how to implement power management as well.

[quytranpzz]

@bjarki-andreasen , Thank you. I initially considered using the comparator driver, but it doesn't fully meet the functionality. The LVD (low-voltage-detection) only monitors the VCC supply (some MCUs have an additional CMPA pin) and triggers when the voltage crosses fixed thresolds, typically generating a reset, an interrupt, or doing nothing. We also have support for a comparator on this MCU, but it uses a different hardware IP

[bjarki-andreasen]

A device does not need to meet the full functionality of a device driver API, most devices in fact don't :) Drivers return -ENOTSUP if the application tries to make a specific device do something which it does not support, so unless the LVD has features which are not covered by the comparator API, which it seems it does not, its perfectly fit to use the comparator API to implement the features it does support

[quytranpzz]

Yes, but the LVD usage does not match the comparator description and may confuse users.
comparator: "Compares the voltages of two analog signals connected to its negative and positive inputs"
LVD just "compares VCC supply with voltage threshold"

[bjarki-andreasen]

Right, the voltage threshold is the negative input, and VCC the positive input, in which case if VCC is above the threshold, the output will be 1 (high) :) Just because the inputs can't be freely selected does not make the hardware "not a comparator" does it?

[bjarki-andreasen]

Like this

.

removing my request for change as this will likely evolve to something else. Happy to re-review in the future if there are still significant documentation or sample bits in it.