[U-Boot] Mips: start.S Questions

[Detlev Zundel]

Hi Peter,

>     Why should it?  I presume the CPU starts at _start, so it will "b
>     reset", i.e. branch (jump) to "reset" and be happy.  Its only if the CPU
>     jumps to one the reserved vectors that it will loop.  And well, as they
>     are reserved, this is a legal thing to do, no?  As the purple port
>     works, I'm pretty sure they do not usually get jumped to there ;)
>
>
> I knew I must be missing something, I didn't see that the reset definition
> comes straight under all the other vector calls, so _start just runs through
> all the vectors if for some reason reset returns (twice) and would get trapped
> because of RVECENT(romReserved,2).

It seems to me that you may still be missing the point that a "b reset"
is an unconditional jump, not a call, i.e. we will never return to the
next instruction.  A call would be a "bal reset", i.e. "branch and link"
which puts the address of the next instruction into the $ra register.
One would return with "jr $ra".

As I'm not really into MIPS, please don't ask me why MIPS has branch
*and* jump mnemonics - I don't see how they designate different
concepts.

Cheers
  Detlev

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