How to activate HSE monitoring

Applicable for

STM32MP13x lines, STM32MP25x lines

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1. Article purpose

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

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";
	};

The LPTIM connected to HSI and used for HSE over frequency monitoring has to be be assigned to the Arm^® Cortex^®-A secure context (OPTEE) and to be enabled in counter node in OP-TEE device tree with:

• lptimer3 on STM32MP13x lines :

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

• lptimer1 on STM32MP25x lines :

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

High speed external oscillator (STM32 clock source)

High speed internal oscillator (STM32 clock source) or High speed synchronous serial interface (MIPI^® Alliance standard)

Open portable trusted execution environment