RFA: RL78: Improve interrupt function generation

[nick clifton]

Hi DJ,

>>      * Uses register bank 3 instead of register bank 0 inside the
>>        handler.
>
> I wonder if nested interrupts will cause problems, since the second
> interrupt will occur with RB3 already selected.

Yes - in fact this appears to be a general problem with RL78 interrupt 
handlers.  There are no instructions to push/pop the current bank 
selection, so in order for nested interrupt handlers to work they would 
have to do something like:


   push ax        ; Save AX
   mov  psw, a    ; Get the current register bank selection
   push ax        ; Save it.

   [... rest of interrupt handler code ...]

   pop  ax
   and  a, #0x24
   cmp  a, #0x24
   sknz
   sel rb3
   cmp  a, #0x20
   sknz
   sel rb2
   cmp  a, #0x04
   sknz
   sel rb1
   cmp0 a
   sknz
   sel rb0
   pop  ax

Which sure seems messy to me.  Is it reasonable to say that C based 
interrupt handlers cannot be nested, or would you like me to extend the 
current patch to  generate prologues/epilogues as suggested above ?


> Also, there are some hand-coded routines in libgloss/libgcc that
> manually swap banks, they'd have to be checked to see if there are
> issues there.  Perhaps the G10 work there solved it already.

There are ?  I did not find any.


> Those, plus Vinay's patch, should be OK otherwise.

Vinay's patch was based on the RL78 backend supporting the G10 
architecture variant, which it currently does not.  So I am attaching a 
revised patch which includes my ISR improvements, Vinay's G10 ISR 
improvements and the addition of G10 support to the RL78 backend.  What 
do you think of this version ?

Cheers
   Nick


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