🚀 go-pugleaf

wam.UMD.EDU!rick@decwrl.dec.com asked the question:
> Where in the source do the lowcore vectors get saved
> and replaced by the panic calls?

     The exception and interrupt vectors are initialized by a function
called vecinit.  It is not listed in the book, but it is called by
macinit on p. 248.  Vecinit simply swaps the values in the array lowcore
with those starting at memory location 0.  The array lowcore is in
lowcore.s, p. 438.  Vecinit does not touch the locations in low memory
that correspond to entries in lowcore that contain 0.  Notice that Xinu
has to be careful to call vecinit only once, not calling it on
subsequent reboots after it has already been called.  Here is the source
code for vecinit:

/* vecinit.c - vecinit */

#include <kernel.h>
#include <macvars.h>

extern	int	*lowcore[], *endvec;	/* New interrupt vectors	*/

/*------------------------------------------------------------------------
 *  vecinit  --  initialize exception, interrupt and trap vectors
 *------------------------------------------------------------------------
 */
vecinit()
{
	register int	v, *swap;

	for (v = 0; v < &endvec-lowcore; ++v)
		if (lowcore[v] != 0) {
			swap = intvec[v];
			intvec[v] = lowcore[v];
			lowcore[v] = swap;
		}
	setdebug(intvec[DEBUG]);
}

/*------------------------------------------------------------------------
 *  setdebug  --  set interrupt switch interrupt vector to specified value
 *------------------------------------------------------------------------
 */
setdebug(newvec)
int	*newvec;
{
	register int	v;

	if (_newrom() == 2)		/* Mac II: set level 7 vector	*/
		intvec[DEBUG] = newvec;
	else				/* Otherwise: set levels 4-7	*/
		for (v = INT4; v <= DEBUG; ++v)
			intvec[v] = newvec;
}

					Steve Munson
					sbm@Purdue.EDU
					sbm@Purdue.CSNET
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