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";
};
Moreover the LPTIM connected to HSI and used for HSE over frequency monitoring has to 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
:
- on STM32MP13x lines
&lptimer3 {
status = "okay";
counter {
status ="okay";
};
};
- on STM32MP2 series:
&lptimer1 {
status = "okay";
counter {
status = "okay";
};
};