How to reflash NOR using the debug board and no userspace

Werner Almesberger werner at
Fri Aug 1 02:41:08 CEST 2008

Rod Whitby wrote:
> No, I haven't wiped it clean.  I've got a GTA02 which seems to be unable  
> to get past the initial NOR u-boot due to Glamo problems (see the other  
> thread).

Oh, it's *that* machine. Now I get it.

> When the machine first powers on, what is the first piece of code to run  
> - NAND u-boot or NOR u-boot?

That depends on whether AUX is held (*) at the time of reset. AUX
connects to the OM0 pin of the CPU, which determines the boot source.

If AUX is not held, the CPU boots from NAND and never looks at NOR
(unless it is told to, which would be much later). If AUX is held,
the CPU boots from NOR and never looks at NAND.

I think you could even unsolder the memory you don't need and the
system would still work. Okay, unsoldering the NAND from the MCP may
be tricky ;-)

(*) There's a slight emphasis on "held". Since AUX affects NOR and
    NAND (Steppingstone) address space anytime, not only at reset,
    the behaviour of the system becomes undefined if the state of
    AUX changes within ~200 milliseconds after reset. See the thread
    at [1] for details.

    Once we're past initial system bringup, u-boot runs from RAM and
    then remaps the vectors such that address space changes caused
    by AUX do not affect operation. (You could still observe them by
    looking at what happens at physical addresses starting at 0.)


- Werner

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