Very Computer

How do you call a C routine from an interrupt in sas-c??

Whenever I try to do it, the machine locks up.

the C routine looks like this:

----- cut ---
LONG Counter = 0;

void VBLRoutine(void)
{
        Counter++;

Quote:}

----- cut -----

and the assembly vertical blank interrupt like this :

----- cut -----
; some includes, don't remember precicely

        XDEF _VBLRoutine
VertBlankServer
        jsr _VBLRoutine
        moveq   #0,d0
        rts
----- cut -----

Now, when I don't call the C routine, but increase the Counter by using
(a1), everything is fine. But when I call the C routine. the machine just
locks.

Now, the VBL is not supposed to just add a counter, it is just a test :-)

--

===========================================================================
Fighting for peace is like *ing for *ity.

__interrupt __saveds IRoutine(void)
{
   blah blah blah++

Quote:}

The __interrupt insures SAS will set the CCR on return, and disables stackchecking.
Be sure that stack extension is turned off.

Finally, the __saveds is desperately needed if you try to access variables.  The
C code will access your variables as an offset from A4.

For example,

   count += 5;

would become

   addq.l #5,_count(a4)

The problem is this.  Without __saveds, your program (C-code) will not have a4 set.

Imagine this

assembly code:
   move.l a3,a4
   lea 24(a4),a0  (just misc code)
   addq.l #1,d0
   jsr _interrupt(pc)
   move.l d0,(a3)+
   rts

C code
{
   count++;           addq.l #1,count(a4)

Quote:}                     rts

This will crash, since A4 was tampered with in the Asm part previously.  The __saveds
keyword will change the "interrupt"routine to look more like this:

C code
__saveds interrupt(void)
{
                      move.l __saveds(pc),a4
   count ++;          addq.l #1,count(a4)

Quote:}                     rts

Hope this helps.

Ian J. Einman

Quote:>How do you call a C routine from an interrupt in sas-c??

>Whenever I try to do it, the machine locks up.

>the C routine looks like this:

>----- cut ---
>LONG Counter = 0;

>void VBLRoutine(void)
>{
>    Counter++;
>}
>----- cut -----

For SAS C:
void __interrupt __saveds VBLRoutine(void)
{...}

__interrupt disable any stack checking (if not disabled at all), __saveds
gets A4 to point at your local data.

--
Ruud van Gaal
MarketGraph Visual Automation

DoomShell 4.5 homepage: http://www.xs4all.nl/~jwkorver
"...Works fascinates me. I could sit and watch it for hours..."

Use the __saveds keyword to set up your global data pointer (A4).
Or, put __far on the Counter variable's definition.  Or compile
with DATA=FAR.  Or compile with SAVEDS.

Please read your SAS/C manual for information about when you should
use  __saveds or related options and keywords.

--

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Any opinions expressed are mine, not those of SAS Institute, Inc.