Portenta H7: schematics wrong - MCU XTAL is 25 MHz

Official Hardware Portenta Family Portenta H7
1

This board drives me crazy:
I see in schematics, MCU gets external clock as 27 MHz. I think I saw also in code that HSE_VALUE is/was set to 27000000.

So, if you use Arduino code which assumes XTAL frequency is 27 MHz - you might get a result as 480 MHz (nominal) MCU core clock. But it is NOT correct: your MCU might run slower, e.g. just with 450 MHz.

I can confirm: My board has external MCU clock as 25 MHz (not 27 MHz).
And changing code to:

    /* Make sure that HSE_VALUE is set properly - it looks like Portenta H7 uses a 25 MHz XTAL, not 27 MHz as shown in schematics! */
#if HSE_VALUE == 25000000
    RCC_OscInitStruct.PLL.PLLM = 5;
    if (lowspeed) {
        RCC_OscInitStruct.PLL.PLLN = 40;
    }
    else {
        RCC_OscInitStruct.PLL.PLLN = 192;		//192 = 480 MHz - with a 25 MHz XTAL!
    }
#endif

sets the clock correctly.

I could confirm via SPI2 PLL clock config: it makes only sense when 25 MHz is there. Now my SPI clock speed is correct with the expected speed (but not with assuming 27 MHz).

Here is a modified file "system_clock_override.c":
system_clock_override.c (11.1 KB)

2

Yes, there are some ambiguities with the crystal values. Both 27 and 25 MHz values are found in source code and schematic.
It has been mentioned here some times:

I guess that some early boards were using 27 MHz but because we don't have a clear changelog of the boards revisions, is it difficult to tell.

3

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