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Where can I find default settings for boot clock fuses and how to make sure the GPIOs are in a safe state after XTAL fails?

Question asked by Stefan Mitterhauser on May 14, 2020
Latest reply on Jul 6, 2020 by Stefan Mitterhauser

Hello,

this table shows different core clock frequencies for different fuse settings

so BOOT_FREQ is setting CORE to 396 MHz or 528 MHz and the Bus frequency always to 132 MHz.

 

 

Then there are the divider LPB_BOOT fuses

My questions are:

  • Is there somewhere a table for RT1020 which specifies which fuses are burned by default and which are not? I want to know which clock frequencies the Boot ROM is setting.
  • Does LPB_BOOT divide core and bus, only the core frequency or does it set the divider from core clock to bus clock (e.g. 132 MHz bus clock is not possible for 396 MHz core clock because that would need LPB_BOOT div by 3)?
  • Does bus clock mean ipg_clk_root?
  • Which clock source will be used for the first start after power was removed e.g. will it use the external 24 MHz XTAL from the beginning or will it use the internal RC oscillator and switch to XTAL as soon as the XTAL is stable? I can't find information about that in the reference manual.

Kind regards,

Stefan

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