Date: 3 May 88 11:21:48 GMT
Comment:  Extracted from Info-Atari16 (INFO-A16) digest number 88-235
From: mcvax!philmds!leo@uunet.uu.net  (Leo de Wit)
Subject: lasterr.c Bomb lister
To: info-atari16@score.stanford.edu

Having recieved a few enthousiastic reactions for the Bomb detector program,
here is it. You can run it afterwards whenever a bombing has taken place.
The main pre is that it does not have to be resident and that it is an
ordinary C program (what is ordinary C? :=).

The program is called LASTERR and compiles succesfull on a Lattice-C compiler,
so note that int == 4 bytes, and short == 2 bytes!
It could be cleaned up a bit, replacing the 'magic numbers' by macro's etc.
It is mainly self-explainatory; the data referenced (addresses 0x380 etc.)
have already been filled in by the standard error routine (the one that also
throws bombs).

------------------------------- CUT HERE --------------------------------------

/* lasterr.c: report last occured error and stack dump.
 * Copyright L.J.M. de Wit, 1988.
 * This source and the generated code may be freely distributed, if not used
 * commercially.
 */

#define PEEKB(a)  (*(unsigned char  *)(a))
#define PEEKW(a)  (*(unsigned short *)(a))
#define PEEKL(a)  (*(unsigned long  *)(a))

main()
{
    int ssp, i;

    ssp = gemdos(0x20,0);    /* switch to supervisor mode, save stack pointer */

    if (PEEKL(0x380) != 0x12345678) { /* magic marker */
        printf("No error occured since last reset\n");
    } else {
        static char *errmsg[] = {
            "Reset", "Reset",
            "Bus error",
            "Address error",
            "Illegal instruction",
            "Division by zero",
            "CHK",
            "TRAPV",
            "Privilege violation",
            "Trace"
        };
        short excepno, offset;

        excepno = PEEKB(0x3c4);
        offset = ((excepno == 2) || (excepno == 3)) ? 8 : 0;

        printf("Exception no. %d (%s)\n",excepno,
            (excepno >= sizeof(errmsg)/sizeof(errmsg[0]))
            ? "Unassigned" : errmsg[excepno]);

        for (i = 0; i < 8; i++) {
            printf(D%d : %8x\tA%d : %8x\n",
                i, PEEKL(0x384 + 4 * i), i, PEEKL(0x3a4 + 4 * i));
        }
        printf(PC : %8x\tUSP: %8x\nSR : %8x\n",
            PEEKL(0x3ce + offset), PEEKL(0x3c8), PEEKW(0x3cc + offset));

        if (offset == 8) { /* exceptions 2 and 3 */
            short status = PEEKW(0x3cc);
            static char *accmode[] = {
                "unassigned",
                "user mode data reference",
                "user mode program reference",
                "unassigned",
                "unassigned",
                "supervisor mode data reference",
                "supervisor mode program reference",
                "interrupt acknowledge"
            };

            printf("\nRead/Write  : %s\n",
                (status & 16) ? "read" : "write");
            printf("In-/Extern  : %s\n",
                (status & 8) ? "extern" : "intern");
            printf("Access mode : %s\n",accmode[status & 7]);
            printf("Address     : %8x\n", PEEKL(0x3ce));
            printf("Instruction : %8x\n", PEEKW(0x3d2));
        }
    }
    gemdos(0x20,ssp);
}

------------------------------- CUT HERE --------------------------------------

I hope no errors have crept into the source while I was typing it over; but
then, you could use this program to see what bomb was produced ( :=)).
Have fun!

        leo.    (What you C is what you get).