From: brian AT apt DOT bungi DOT com (Brian Litzinger)
Subject: How do I read my memory mapped device at d000:0000?
To: djgpp AT sun DOT soe DOT clarkson DOT edu
Date: Sun, 29 Nov 92 3:04:18 WET
Reply-To: brian AT apt DOT bungi DOT com

I have a memory mapped board at d000:0000 in my machine.  The first
four bytes contain 0b 01 22 22.

I wrote and compiled the following program under djgpp 1.09:

    #include <stdio.h>

    main(int argc, char *argv[]) {
	unsigned long *a = (unsigned long *) 0xf00f0000L;
	    
	printf("0x%08x\n",*a);
    }

When run, it correctly displays the first four bytes of my AMI BIOS.
However, when I change where a points to to:

	unsigned long *a = (unsigned long *) 0xf00d0000L;

which should be the beginning of my card at d000:0000 and run the program
I get:

    Exception 13 (0xd) at eip:108d

at the instruction that is actually attempting to do the access
to 0xf00d0000.

If I run under debug32, I can issue the command 'm 0xf00d0000' before
or after the exception, and it correctly displays the bytes from the
memory at d000:0000.

So where did I mess up?

I'm running on an Intel 486/33 with 8MBs Ram.

brian AT apt DOT bungi DOT com