Re: Interrupt Attribute for 68K

[Scott Howard <scott@objsw.com>]

David Williams wrote:
> 
> Hi all,
> 
> There was a discussion on this mailing list about a month and a half ago
> about having an interrupt attribute for functions. I am coding some
> interrupt handlers for a 68000 target (DragonBall) and would like to use
> the interrupt attribute for functions that will be interrupt handlers.
> 
> 1. Is this supported for 68K targets?

Our next release of gcc (based upon egcs-1.1.2) will include support for
the interrupt attribute, on 68k targets.

> 2. Is there already some source code for set and get interrupt vectors for
> 68K targets?

The easiest way to 'get' and 'set' vectors is to simply define the
vector table as an array of pointer to function returning void, eg 

extern void (*exceptiontable) (void) [256];

To set a vector, let's say the 'divide by zero' vector:

exceptiontable [5] = MyDivByZeroHandler;

(I suppose it's obvious, but the table must be located in RAM for this
to work.)

Our next compiler release will include a linker script for ROM-based 68k
systems which (among other things) creates an exception vector table in
ROM. If user code defines a handler for a particular vector, then the
linker will set that vector to the address of the user code; otherwise
the vector is set to the address of a user-defined 'default' handler.
This avoids having to 'get' and 'set' vectors at run time.

Scott Howard
scott@objsw.com
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