Re: [avr-gcc-list] source code of crtm48.o

[Joerg Wunsch]

Erik Christiansen <address@hidden> wrote:

> For assembler ISRs, it appears to be " a name like __vector_N should
> appear, with N being a small integer number."

Well, rather use preprocessed assembler instead (filename suffix .S,
the capital letter `S'), and feed it through the compiler instead the
assembler.  (The compiler driver will then chain the preprocessor
together with the assembler.)  Then,

#include <avr/io.h>

..global SIG_INTERRUPT0
SIG_INTERRUPT0:
        your
        isr
        goes
        here

        reti

> A trial build should show a handler for ISRs not "installed", at
> "__vector_default", if I've understood the doco correctly. How that
> would avoid competing for an interrupt that you wish to handle in
> assembler, is not quite clear to me yet, since I haven't tried it.

The vectors are pre-bound to so-called `weak symbols'.  These symbols
satisfy the linker's search for undefined externals, but any non-weak
(global) symbol (supposedly supplied by the application itself) will
get precedence.  That way, your vector as declared above will get
linked, instead of the jump to __vector_default.  Note that
__vector_default itself is also a weak symbol (jumping back to address
0 as supplied by the library), so your application can overload it
with whatever seems reasonable.

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