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jmf1
jmf1
Associate III
June 20, 2024
Solved

stm32H7 - USB application - HSE or HSI+CRS

  • June 20, 2024
  • 1 reply
  • 2883 views

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

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Best answer by 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.)

1 reply

AScha.3
AScha.3Best answer
Super User
June 20, 2024

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.)

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jmf1
jmf1Author
Associate III
June 20, 2024

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
AScha.3
Super User
June 20, 2024

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 .

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