i.mx8 mini, alternatives to uart debug (A53 vs M4)

[dav1]

Hi,

1. On the imx8 mini, what are the best alternatives to get early print logs from the A53 and/or M4?
      ...all 4 UART's are taken for other things, so can't use these.
   
   The most convenient would be to run it over a composite usb with cdc
   Jtag would also be a good option since it doesn't eat any valuable gpio's...
   
   
   
2. Is there any activity or prints on the two uarts during cold-boot / ROM (Serial Downloader)?
   or is all of this explicitly activated in u-boot?

[CarlosCasillas]

Hi,

Yes, you could implement a USB-Serial for secondary Debug option, but it is required to first boot the system to load the USB drivers/classes, so, it won’t be available on early boot stages.

Regarding activity of other pins during the boot, they are the boot selector GPIOs that may select entering to serial downloader mode, which could be implemented by USB or by UART. Please refer to Figure 6-1 “Boot flow” of the i.MX8M Mini Reference Manual.

Hope this will be useful for you.
Best regards!
/Carlos
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[dav1]

HI Carlos,

Can you please clarify that there aren't any UART prints made from within the on-chip boot ROM.

i.e. all UART activities are explicitly activated in uboot, correct?