Boot problem phycore AM335x

[Martijn]

Hi guys,

For my graduation I developed my own board to sniff out PLC communication.
Now I'm running into some problems and I was hoping you might be able to
help me out/have some good tips.

As processor I chose a SoM: phycore AM335x
(https://www.phytec.eu/product-eu/system-on-modules/phycore-am335x-download/).
>From an SD card the SoM has to be booted but I run into problems that hamper
the progress and I can't get out. 
My SDIO circuit looks good and the SoM detects the SD card as well.
I followed the steps for flashing the correct OS on the SD card as described
by the supplier.

Through an RS232 interface I can read the SoM, so I also have some logging.
In the attachment a screenshot of the logging is added.
After 5 seconds the SoM seems to go into sleep mode and pretty little
happens. In the datasheet of the AM335x I can partly trace what is happening
(page 5029 of:
https://www.ti.com/lit/ug/spruh73q/spruh73q.pdf?ts=1599120014623). It does
not see any bootsources so when the watchdog time is up the process is
stopped.

I didn't "wire out" the SYSBOOT pins of the processor (which might not be
very handy afterwards) but the processor should be able to boot from the SD
card.

Do you have any tips or ideas what the problem might be?
Like to hear from you.

Kind regards,

Martijn




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