some progress

Ed Sutter edsutterjr at
Wed Jul 1 03:55:30 UTC 2015

I made some progress regarding boot from sd...
I took a step back and decided to get the LEDs initialized.
Doing that allows me to work with a simpler device to verify startup.

Anyway, I managed to get the GPIO pins initialized correctly so
that I could control the LEDs.  Then I built a SD card with the
proper prefixes etc.. in there and was able to boot up the led
pattern as expected.

That tells me that it boots correctly, but is not initializing the UART
as it should. On the other hand, since our UART-boot does work, we can
at least say that the code in cpuio.c currently is NOT breaking the
uart initialization that the rom-bootloader does for us.  So, my hunch
is that some clock that drives the UART is not being turned on in our
code (but it is turned on when the bootloader is forced to boot through
the UART).

Anyway, that's my state at the moment.  Done for the night.
The one tricky part that I'm glad to have out of the way is the prefix
needed at the base of the image.  That wasn't obvious to me.


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