Still undergoing attempt to boot Umon from SD

Jarielle Catbagan jcatbagan93 at
Tue Jun 30 01:24:25 UTC 2015

On Jun 29, 2015 5:33 PM, "Ed Sutter" <edsutterjr at> wrote:
> Jarielle,
> Ok, I think I may have stumbled on some "hope" for the  boot-from-sd card
> 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...

You are correct, I have not completed the cpuio.c file yet.  I was planning
to update it and implement the parts as I proceeded with the porting
process.  I believe that you're absolutely right about the incompleteness
being the cause of the uSD boot to fail.

> 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.

I think you might be onto something.  I was assuming that I didn't have to
worry about initializing the UART as I was under the impression that since
it was already working it wasn't something I had to worry about.  I have no
doubt that my assumption could be wrong all along.

> 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?

It makes perfect sense.  After my attempts at uSD booting, I was already
suspecting that it could be the boot.bin file all along that's causing the
uSD boot to not come through.  I just did not know how to verify at the
time during my attempts.  Hence why it motivated me to get a JTAG debugger.

> 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
> correct.
> Am I making any sense?

Crystal clear. I will look into this right now.

> Ed
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