How to activate HSE monitoring

Applicable for

1. Article purpose[edit source]

The purpose of this article is to explain how to monitor the HSE oscillator.

If the HSE oscillator is used in the clock tree, it is possible to enable a monitoring function to detect and avoid over frequency. The LPTIM mechanism can detect any over frequency and triggers a tamper event which runs the appropriate custom actions.

2. How to activate the monitoring[edit source]

By default, the HSE monitor is disabled in the dtsi "SoC" files.

To activate the HSE monitor, add this node in your board OP-TEE device tree

	&hse_monitor {
		status = "okay";
	};

Moreover the LPTIM connected to HSI and used for HSE over frequency monitoring (lptimer3 on STM32MP13x lines and lptimer1 on STM32MP25x lines ) has to be be:

assigned to the Arm^® Cortex^®-A secure context (OPTEE)
enabled in counter node in your board OP-TEE device tree with:
- on STM32MP13x lines :

	&lptimer3 {
		status = "okay";
		counter {
			status ="okay";
	 	};
	};

on STM32MP25x lines :

	&lptimer1 {
		status = "okay";
		counter {
			status = "okay";
		};
	};