Still undergoing attempt to boot Umon from SD

Ed Sutter edsutterjr at
Tue Jun 30 00:33:40 UTC 2015

Ok, I think I may have stumbled on some "hope" for the  boot-from-sd card stuff...
I'm looking at the cpuio.c that is currently in master and unless I'm missing something,
it appears to be incomplete.  That incompleteness may explain why your uSD boot
attempts didn't succeed.  Here's what I'm thinking...

When the rom bootloader starts up, it first attempts to boot from SD card, then if that
fails it falls through to the UART.  When we do the boot from UART stuff, it works, but I
think the current version in master is working "luckily"...
Think about it... for the bootloader in ROM to interact with the UART to run an XMODEM
download, IT has to initialize the UART.  So, the code it downloads (boot.bin) doesn't even
have to do that and it will still appear to work.

Now, if we're trying to use that same boot.bin to boot from SD (earlier in the boot sequence
than the UART; hence possibly the UART is not initialized) , then its possible that the
bootloader hasn't initialized the UART at the time of the SD boot attempt.  That would
mean that our current boot.bin would not boot properly because it doesn't have the code in
it to initialize the UART.

Know what I mean?

I believe I have that UART initialization code.  My version of this (which I did about 6 weeks
back) has the UART initialization in there.  Its hard to tell if its right, simply because it still
may be depending on the bootloader's initialization for something; however, I *think* its

Am I making any sense?

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