Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!utgpu!water!watmath!clyde!rutgers!ucla-cs!zen!ucbvax!decvax!gsg!ariola
From: ariola@gsg.UUCP
Newsgroups: comp.sys.ibm.pc
Subject: Use DOS interrupt 1C (timer tick) from MSC help needed
Message-ID: <338@gsg.UUCP>
Date: Wed, 2-Sep-87 18:11:44 EDT
Article-I.D.: gsg.338
Posted: Wed Sep  2 18:11:44 1987
Date-Received: Fri, 4-Sep-87 04:36:07 EDT
Lines: 66
Keywords: MS-DOS timer interrupt MSC clock

System:		IBM PC/AT compatible
Sofware:	running DOS 3.20, MSC vresion 4.0
Problem:        use type 1C timer interrupt from a C program.

I tried to modify interrupt service routine of type 1C from my main
program (see main.c below) to be function 'ciao' which is written in
assembly (see file ciao.asm below).  I thought I followed all the
instructions among 5 different DOS reference books but I was not able
to make it working properly.  What happened was: the control is
transferred to ciao but the segment registers are all screwed up and
the machine halts.  Can someone points out what's wrong with it?
Thanks in advance...  (BTW, I was using codeview to debug this.)
 
The following is the source code for assembly routine ciao.asm and
its calling C program int.c:
----------------------------------------------------------------------
;	Static Name Aliases
;
	TITLE   ciao1
;	NAME    ciao1.C

	.287
_TEXT	SEGMENT  BYTE PUBLIC 'CODE'
_TEXT	ENDS
_DATA	SEGMENT  WORD PUBLIC 'DATA'
_DATA	ENDS
CONST	SEGMENT  WORD PUBLIC 'CONST'
CONST	ENDS
_BSS	SEGMENT  WORD PUBLIC 'BSS'
_BSS	ENDS
DGROUP	GROUP	CONST,	_BSS,	_DATA
	ASSUME  CS: _TEXT, DS: DGROUP, SS: DGROUP, ES: DGROUP
_TEXT      SEGMENT

	PUBLIC	_ciao
_ciao	PROC NEAR
	;	Do nothing, just return from interrupt
	iret	

_ciao	ENDP
_TEXT	ENDS
END
----------------------------------------------------------------------
#include	<dos.h>

extern ciao();

main ()
{
	union	REGS	irg, org;	/* input, output registers */
	struct	SREGS	srg;		/* segment registers */
	struct	{
		unsigned int	seg;
		unsigned int	off;
	} c;
	char far *p;

	p = ( char *)((long)ciao);
	segread(&srg);

	c.off = FP_OFF(p);  c.seg = srg.cs;
	srg.ds = c.seg;  irg.x.dx = c.off;  irg.h.ah = 0x25;  irg.h.al = 0x1c;
	intdosx(&irg, &org, &srg); 	/* set 1C interrupt to: ciao */
	for (;;)
		printf ("wait...");
}