Re: [avr-libc-dev] Interrupt vector redirection scheme

[Michael Schulze]

Hi Dave,

> > If you want to allow that behavior in C, it looks like that:
> >
> > typedef void (*funcpointer)(void);
> >
> > funcpointer     fp;
> >
> > ISR(TIMER1_OVF_vect) { if (fp) (*fp)(); }
> >
> > Attention: The function pointer has to be set with interrupts
> > disabled, because of changing a word and on the AVR isn't
> > atomically.
>
> There's already a vector table. Each entry consists of an rjmp (or 
> jmp) instruction to a named routine.

Yes, of course and I know this. The redirection scheme of me uses the 
vector table and provides a way for binding ISRs at runtime. In my 
opinion, the above C-code is functional equivalent to my proposed 
solution. However, my scheme is cheaper in terms of resource usage.

> Right now the ISR macros uses numbers to line up the routines. By
> creating a new macro which declares the ISR handler correctly, but
> uses a name rather than a number, you could then write a function
> which fabricates the appropriate rjmp (or jmp) instruction and stuffs
> into the existing vector table. No performance hit at all.

Sorry, but I don't understand what you meant. Could you it explain? 
Allows your scheme dynamic changing of ISRs at the runtime?

Regards,
Michael

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