Re: [avr-gcc-list] Customizing interrupt vector entries when using GCC?

[Joerg Wunsch]

(Please don't crosspost.)

Rick Mann <address@hidden> wrote:

> I'm working on an ATmega128, using avr-gcc, and I need to speed up
> the handling of interrupts on three pins INT5, INT6 and INT7. Rather
> than creating three interrupt handlers that all call a single
> unified handler, I'd like to put the same handler in each of those
> three slots in the vector.

The obvious solution would be to write all of it in assembly language,
and supply multiple labels to the ISR:

#include <avr/io.h>

..global INT5_vect
INT5_vect:
..global INT6_vect
INT6_vect:
..global INT7_vect:
INT7_vect:
        ;; do something here
        reti

There's a GCC feature of an `alias' attribute, so in C you could
write:

#include <avr/io.h>
#include <avr/interrupt.h>

ISR(INT5_vect)
{
        /* do something here */
}

void INT6_vect(void) __attribute__((alias("INT5_vect")));
void INT7_vect(void) __attribute__((alias("INT5_vect")));

Alas, when trying this, GCC says:

foo.c:9: warning: alias definitions not supported in this configuration; ignored
foo.c:10: warning: alias definitions not supported in this configuration; 
ignored

(Also, I'm not sure whether the macro expansion for INT5_vect would
work inside the double quotes, probably not.  Perhaps you'd have to
write __vector_6 instead.)

Finally, you could apply the alias on the linker command-line.  For my
simple example, the respective compiler command would look like:

avr-gcc -mmcu=atmega128 -Os \
-Wl,--defsym=__vector_7=__vector_6 \
-Wl,--defsym=__vector_8=__vector_6 \
-o foo.elf foo.c

As you can see, plenty of options without really touching gcrt1.S. :)

-- 
J"org Wunsch                                           Unix support engineer
address@hidden        http://www.interface-systems.de/~j/