Unable to HAL_RTC_SetTime in STM32U585 with TrustZone enabled

[erosghignoni]

Hi 

I am working on an STM32U585 microcontroller with TrustZone enabled and I need to update the RTC time with the HAL_RTC_SetTime function. During the execution of that function, the line

status = RTC_EnterInitMode(hrtc); //stm32u5xx_hal_rtc.c

returns HAL_TIMEOUT, so I am unable to update the RTC values. 

I have attached several screenshots that show the microcontroller configuration The Project Manager generates both MX_RTC_Init functions for the Secure and NonSecure zones. 

The main files of both Secure and NonSecure zone execute the MX_RTC_Init function without any errors, the software starts up correctly, but at some point I am not able to set the RTC Time. 
Upon debugging, I noticed that during the execution of RTC_EnterInitMode, the line

SET_BIT(RTC->ICSR, RTC_ICSR_INIT);

does not set the INIT bit, which remains at 0. 

Thank you in advance for your support. Please let me know if you need any further information.

Best regards,
Eros

[Saket_Om · Accepted solution]

Hello @erosghignoni 

If you need to update the RTC from NonSecure code while the RTC is configured as Secure, you should implement a Secure callable function using the CMSE_NS_ENTRY attribute. This function is defined in the Secure zone and exposes a controlled interface for NonSecure code to request RTC updates. For example, you can create a function like SECURE_SetRTCTime, which takes a pointer to an RTC_TimeTypeDef structure and internally calls HAL_RTC_SetTime to update the RTC. The NonSecure application can then invoke this Secure function via a function pointer, ensuring that all RTC modifications are performed within the Secure context, maintaining the integrity and security of the RTC peripheral.