[Battlemesh] [FCC] What hardware still works?

[David Lang]

On Tue, 23 Feb 2016, Bastian Bittorf wrote:

> * Adam Longwill <adam.longwill at metamesh.org> [23.02.2016 19:53]:
>>> Anyone have a Explain it Like I'm 5 version out there to help explain?
>
> JTAG: you are talking directly with a chip and pushing bits into it
> SERIAL: you are speaking with software (e.g. bootloader or linux)
> TFTP: the same but very limited but via network (mostly ethernet)
>
> so:
> serial/tftp needs a lot of stuff to work *for* you.
> if someone decides to not implement/forbid it,
> this will not work for you.
>
> JTAG: it's some layers lower and *meant* for fallback/debug
> the chips directly (see wikipedia). this will "always"(tm)
> work, but the soldering points are for "advanced" users.
> back in the old days i did it several times for the WRT54G...

no, JTAG will not "always" work, many/most chips have a fuse you can blow on 
them that will prevent part of the built-in flash from ever being re-written.

now, most vendors are not going to blow this because they want the backdoor to 
be able to fix mistakes as well. But if someone starts going to the effort of 
locking down the bootloader that's available via serial, then why not go the 
extra step and prevent the bootloader from being modified.

David Lang