Update: uMon is now booting from SD

Ed Sutter edsutterjr at gmail.com
Sun Jul 5 01:02:30 UTC 2015

On 7/4/2015 2:29 PM, Jarielle Catbagan wrote:
> Great to hear that it's working now!
Yep,  I will go ahead and push the patches as they are (since I was able to
verify the build), but we still need some documentation or a script on the
procedure for building the SD card.
> For the "raw" mode, a Configuration Header TOC Structure had to be
> prepended before the GP header, am I right?
Right, and that is placed at the base of the SD card (or at one of a few offsets)
just using 'dd'.  I can add that if you want me to.
> What are the other tasks that you would recommend I pursue.  I am
> thinking of getting the DDR initialization working and then Ethernet.
> What are your thoughts?
Definitely DDR init should be next on the list.  After that, Ethernet is a good candidate,
however one other more fundamental interface is MMC.  Think about the actual
bootup of a full-blown bootmonitor that is then capable of loading an RTEMS application...

First of all, we're building the "MLO" as they call it.  As we know, that image is pulled from
SD (or EMMC) directly into SRAM.  This is the first stage, and I think we're almost there.
Next, the program needs to initialize DDR and then load the FULL uMon into DDR.  To do that
the MLO needs to be able to read from the SD card.  So it seems to me that the MMC interface
to the SD card is really the next most important interface to tackle.

Lets think about this a bit.  Obviously both interfaces are needed; but my personal opinion is
that the ability to read from MMC is more fundamental.  Actually, a functional BBB boot
monitor *could* run without Ethernet as long as it had the ability to load from SD.
Let me know what you think...

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