booting from NOR (GTA02)

Michael 'Mickey' Lauer mickey at
Sun Jan 13 00:53:49 CET 2008

Werner Almesberger wrote:
> As of r3819, this works now. I still need to make it ignore the
> environment (which it fetches from NAND, and which may contain nasty
> surprises), but that's less urgent.

> However, there's one subtle detail that's quite interesting: we can
> check the boot mode (i.e., whether NOR or NAND) by reading the OM[1:0]
> bits through the BWSCON register.

> As it turns out, BWSCON reflects the _current_ status of OM[1:0],
> i.e., after doing a "reset halt" in OpenOCD while holding down AUX,
> and then releasing AUX (after all, it's kinda inconvenient to type
> when one hand it busy with the GTA02), BWSCON will happily read all
> zero.

> Even better, this also changes whether we see Steppingstone (followed
> by zeroes) or NOR at address 0. u-boot copies itself away quickly
> enough (and, in fact, we could just jump to the permanently visible
> copy of the NOR at 0x18000000 if we're in a great hurry), so this
> doesn't cause any real issues.

> But it surely made debugging this little feature a lot more exciting
> than I expected ...

Awesome news -- this can be really handy! Thanks. Once in a while, a
positive surprise makes us feel so much better...



Dr. Michael 'Mickey' Lauer | IT-Freelancer |

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