STM32U535: SPI2 Stops Working When TRNG Enabled in CubeIDE

[Badrinathan]

Hi @all  @stforum @stforum2  @stforum.tormod9  @stforum23 @jkn_stforum 

I’m using STM32U535CBTx MCU, using STM32Cube IDE.

Peripherals in use:

• I2C1

• UART4

• LPUART1

• SPI2

• GPIO PB8, PB9, PB10 for LEDs

Issue:

• SPI2 works fine when TRNG is disabled.

• After enabling TRNG, SPI2 stops working.

I’ve attached both .ioc files (with TRNG enabled and disabled). Could someone please review them and suggest a solution?

Could anyone please:

1. Review my .ioc files

2. Explain why this happens and how to fix this issue?

3. Suggest how to use TRNG and SPI2 together

I have attached two .ioc files for reference:

1. sensor nodewith TRNG.ioc – this version has the TRNG peripheral enabled.

2. sensor node without TRNG.ioc – this version does not use TRNG and SPI2 works correctly.

Please review and help identify why SPI2 stops working when TRNG is enabled.”

Thanks in advance!

[Ghofrane GSOURI]

Hello @Badrinathan 

I'm currently checking this behavior. I will get back to you asap.

THX

Ghofrane

[Badrinathan]

Hi @Ghofrane GSOURI 

Thanks, Ghofrane. I’ll wait for your update.

Thank you
Badrinathan J

[Ghofrane GSOURI]

Hello @Badrinathan 

I compared the two provided IOC files and identified the key differences in the clock configuration:

Without RNG:

The PLL is enabled and used as the system clock (SYSCLK).
MSI is selected as the PLL source.
SYSCLK is derived from the PLL, resulting in a higher system frequency.
Voltage scaling is set to SCALE1, providing the highest performance.
With RNG:

HSI48 (the 48 MHz internal oscillator, required for TRNG) is enabled.
The PLL is disabled (PLLState = RCC_PLL_NONE).
SYSCLK is sourced directly from MSI, not the PLL, leading to a much lower system frequency.
Voltage scaling is set to SCALE3, which is the lowest performance setting.
Recommendation:
To ensure both RNG and SPI2 function correctly, enable HSI48 for the RNG peripheral while maintaining your original PLL-based system clock and high-performance voltage scaling. This configuration will allow both peripherals to operate at their required speeds.

Please try this adjustment, and let me know the results.

PS: I used the latest version of CubeMX6.16.0 , you can download it from the following LINK

THX

Ghofrane

[Badrinathan]

Hello @Ghofrane GSOURI 

Thank you for your prompt response.

I would like to clarify that I am not using CubeMX .
I am configuring everything directly in STM32CubeIDE (latest version) using the .ioc file inside the Cube IDE. I am not manually changing the voltage scaling, but as soon as I enable the RNG, CubeIDE may be automatically switches the Voltage Scaling from SCALE1 to SCALE3. 

Could you please explain step-by-step how to correctly keep:

• PLL enabled

• SYSCLK sourced from PLL

• Voltage Scaling = SCALE1

• HSI48 enabled only for RNG

specifically inside STM32CubeIDE?

In this Cube IDE,  I am not sure where to set the voltage scaling back to SCALE1 or how to prevent CubeIDE from changing it automatically.

A detailed sequence of steps (menu paths, tabs, and settings) would really help me solve this using STM32 CubeIDE.

Thank you,
Badrinathan

[Ghofrane GSOURI]

Hello @Badrinathan 

Here are the steps I followed: I used CubeMX 6.16.0  standalone  and loaded your IOC file (sensor node without TRNG.ioc). I kept your original configuration, then activated the RNG and ensured that HSI48 is selected as the input for the RNG multiplexer. Afterward, I generated the code and chose STM32CubeIDE as the toolchain.

I will review this in STM32CubeIDE and get back to you.

[Ghofrane GSOURI]

Hello @Badrinathan 

Inside STM32CubeIDE, import the attached IOC  

Then generate code