CM4 core clock limited to 64 MHz while CM7 runs at full configured frequency?

[Prathiksha]

I am working on the NUCLEO-H755ZI-Q, which contains a dual-core STM32H755 (Cortex-M7 + Cortex-M4).

I configure the system clocks in CubeMX as follows:

• SPI1/2/3 Clock MUX: 400 MHz
• System Clock: Configured for high-speed operation
• CM7 core frequency: Correctly matches the configured value (e.g., 200 MHz / 400 MHz depending on settings)

However, when I debug or read the CM4 core clock, I always see:

• CM4 clock = 64 MHz
• It does NOT increase even when I configure higher values in CubeMX. 

Regards,

Prathiksha

[AScha.3]

How you "see" the 64Mhz ?

 

[Prathiksha]

These are the below functions used to verify the clock.

• HAL_RCC_GetSysClockFreq() → returns system clock (SYSCLK) in Hz.
• HAL_RCC_GetHCLKFreq() → AHB clock (HCLK).
• HAL_RCC_GetPCLK1Freq() / HAL_RCC_GetPCLK2Freq() → APB clocks.

[TDK]

It's probably an issue with how you're running the program. If the CM7 core is doing the clock configuration, it needs to do that before the clock will be updated. Just running the CM4 side will use the default clock (64 MHz).

[Prathiksha]

Yes, I’m aware that the CM7 core needs to configure the clocks for CM4. While debugging both CM7 and CM4, I ran CM4 to verify the clock because it was showing 64 MHz. I was using DMA for ADC in our project, and since DMA requires a higher frequency, I suspected a clock issue. However, the actual problem was related to DMA.

[mƎALLEm]

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@Prathiksha wrote:

However, when I debug or read the CM4 core clock, I always see:

• CM4 clock = 64 MHz

---

How did you check that?

[Prathiksha]

These are the below functions used to verify the clock.

• HAL_RCC_GetSysClockFreq() → returns system clock (SYSCLK) in Hz.
• HAL_RCC_GetHCLKFreq() → AHB clock (HCLK).
• HAL_RCC_GetPCLK1Freq() / HAL_RCC_GetPCLK2Freq() → APB clocks.

[mƎALLEm]

What API you have used to get the CM4 clock?

Please share your project so we can reproduce the behavior and understand what is going on...

[Prathiksha]

I have uploaded the project file contains both CM4 and CM7. 

[mƎALLEm]

Hello and thank you for the sharing. I don't see where do you get the CM4 in the attached firmware. Could you please clarify?