On 02/25/2011 01:13 PM, Somebody in the thread at some point said:
Hi -
When you cycle the target power using a web interface to the buddy box, you can also select to force a canned boot path sent over bootp, so even a trashed box with no bootloader can be recovered.
not all boards boot when power-cycled (!) and you can't test the default bootloader with this approach (e.g. if your card only boots from SD and you want to test u-boot-linaro on SD, you might not be able to recover from a broken bootloader), but for the kernel that would be fine. I think almost all our current boards boot when power-cycled though.
For PC hardware you can usually either set this on the board or BIOS; all the embedded boards I know of will start up on power coming. I'm willing to believe ones that don't might exist but I doubt they can maintain that sang froid in the face of their power-on button also being overridden at the same time ^^
It's not far away from being workable on embedded boards, maybe by having an adapter card that sites two SD cards in one slot, you can enable the normal one or a backup read-only one based on a line controlled by its buddy box.
adapter card> interesting idea! Does this require us to build custom hardware, or does this exist on the shelves already?
I never saw one; however this exists for $0.71 in quantity
http://www.fairchildsemi.com/ds/FS/FSSD06.pdf
so designing, laying out, and prototyping one is no problem for me to do from here with my existing tools if you should be interested.
I designed a similar emulation board about 12 years ago for smartcard readers, it's the same basic deal.
I guess it should present itself to the buddy box as a USB <-> serial adapter and use one of the unused serial handshake lines from PC direction to control which card is enabled, and another to switch the target power. The actual serial traffic would be the board debug port. These adapter chips are likewise cheap and simple and off the shelf. You could control it with stty without any special driver then.
-Andy