stm32H7 - USB application - HSE or HSI+CRS

[jmf1]

Hello,

I'm a hobbyist and I'm working on a USB to 4xI2S (8 channels using the SAIs) using a stm32H7 MCU. I have a proof of concept working on a stm32F7 discovery board. I'm starting to look at the dedicated board.

I understand that the USB peripheral needs a precise clock, which can't be achieved alone by the internal HSI oscillator, as it is not precise enough. The stm32H7 has a clock recovery system, CRS, to calibrate the HSI with the SOF signal.

Would you have experience with using the HSI+CRS?

Are there tricks in the implementation if the Return of Experience was positive?

Safer to go with a 8Mhz HSE?

Best regards,

JMF

[AScha.3]

Hi,

yes, always better to use HSE / crystal or oscillator .

And for audio...anyway: want best, low jitter clock source. (Never an internal RC-osc.)

[jmf1]

Thanks for the confirmation.

For the audio part, my intention is to feed the SAI with dedicated crystals fit to 48k and 44.1k frequencies.

Best regards,

JMF

[AScha.3]

Right,

or other way round : i use an ES9038 DAC, as SAI master with its own low jitter clock ( AS318-B ), and it can be set to the desired sampling rate . So no clock switching needed . (CPU has its standard crystal, 8M or 24MHz .)

And for USB usually a crystal is recommended for stable connection anyway .