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From: greenber@phri.UUCP (Ross Greenberg)
Newsgroups: net.micro.att
Subject: Accessing the ATT clock while running IBM DOS3.1
Message-ID: <2284@phri.UUCP>
Date: Sat, 15-Mar-86 14:39:38 EST
Article-I.D.: phri.2284
Posted: Sat Mar 15 14:39:38 1986
Date-Received: Mon, 17-Mar-86 03:37:47 EST
Distribution: net
Organization: Public Health Research Inst. (NY, NY)
Lines: 38

A while ago I had to reformat an ATT 6300 with DOS3.1 in order to get
the cluster size down to a reasonable size.  That worked like a
charm --- except that the clock was no longer set upon boot-up.

The following should allow you to create your own "clockset" program.
A version of this is coming out on one of the upcoming PC/BLUE vols.

1)	Call interrupt 0x1a with AH = 0xFE.  This returns the time
	in the registers as you expect, and the date (in the format
	described below) in BX
2)	Do a DOS call to set the time: INT 0x21 with AH = 0x2d
3)	The date is the number of days since January 1, 1984. Forget
	about leap-years --- seems ATT doesn't believe in them.
	A simle kludge to convert:

	year = num_days/365
	num_days -= (year * 365)
	month = 1;
	while (num_days > month_tab[month])
		num_days -= month_tab[month++];

	year += 1984;

4)	Then set up the registers as for a DOS Set date:
		regset.h.dl = num_days;
		regset.h.dh = month;
		regset.x.cx = year;
	and call DOS Int 0x21 with AH = 0x2b.

Voila! You have your date and time back.


-- 
------
ross m. greenberg
ihnp4!allegra!phri!sysdes!greenber

[phri rarely makes a guest-account user a spokesperson. Especially not me.]