USB not working when MCO2 enabled and driven by PLLI2SCLK

[C.East2]

The image shows my clock configuration for the STM32F469IIT. I want a 12MHz output from MCO2 and I found that I could theoretically achieve this using the PLLI2SCLK input. However, when I use this configuration, the device is not recognised by the PC via USB. I have also measured the signal using a scope and I seem to get a frequency of 6MHz. I can increase the clock speed on MCO2 to be "24MHz" and this will produce a 12MHz signal.

I won't post any code just yet as this issue may be more fundamental, but let me know if more information is needed. I hope someone can explain why this doesn't work.

I'm using an external 8MHz clock, USB FS but I am not using the I2S peripheral itself, only the clock divider and multiplexer.

[Lubos KOUDELKA]

Hello,

can you check your HSE crystal is really 8 MHz? Is USB working when you set your PLL parameters for 4 MHz HSE crystal?

From your description and verification using MCO this looks possible.

[C.East2]

Hi @Lubos KOUDELKA​ ,

HSE crystal is definitely 8MHz.

When I select the MCO2 source to HSE, I get 8MHz. I can also use the division to achieve the correct values.

[C.East2]

@Lubos KOUDELKA​ 

I've found that MX is wanting to enable the HSI in the SystemClock_Config (See image below). When I remove 'RCC_OSCILLATORTYPE_HSI' the device works. However, every time I regenerate code from MX, it appears. I can't (from the clock config diagram) where I am enabling/using the HSI. I am using the LSI for the RTC.

[Lubos KOUDELKA]

Yes, I just tried on my side and I can also see problem with RCC_OSCILLATORTYPE_HSI in init, I will report to our developers. Unfortunately now I don't have any easy solution for to skip RCC_OSCILLATORTYPE_HSI after STM32CubeMX re-generation, you will need to do it manually.

[C.East2]

Thanks @Lubos KOUDELKA​ ,

For the time being I can assign HSI to the MCO1. This means it's being used and will not cause an error. It also means I don't have to keep deleting the code after generation. Hopefully a fix can be made.

[Imen.D]

Hello @C.East2​,

Thank you for having reported this issue.

Hi @Lubos KOUDELKA​ Thank you for bringing this post to my attention.

I added CubeMX team @Khouloud OTHMAN​ @Khouloud ZEMMELI​ in this post to review this issue.

Thanks

Imen

[Imen.D · Accepted solution]

Hi @C.East2​ ,

This issue is confirmed and an internal ticket (ID 119067) is submitted in order to fix this in the coming release of CubeMx.

(PS: Internal ticket ID 119067, this is an internal tracking number and is not accessible or usable by customers).

Thank you again for having reported the point.

Imen