Path: utzoo!attcan!uunet!husc6!bloom-beacon!mit-eddie!uw-beaver!tektronix!orca!tekecs!frip!andrew
From: andrew@frip.gwd.tek.com (Andrew Klossner)
Newsgroups: comp.arch
Subject: PDP-10 user I/O (was Re: Hardware-supported user handlers: examples)
Message-ID: <10008@tekecs.TEK.COM>
Date: 20 May 88 17:05:25 GMT
References: <353@cf-cm.UUCP> <3095@edm.UUCP> <20618@think.UUCP> <1988May12.162207.16764@utzoo.uucp> <8722@ames.arc.nasa.gov> <10002@tekecs.TEK.COM> <21671@amdcad.AMD.COM>
Sender: andrew@tekecs.TEK.COM
Organization: Tektronix, Wilsonville, Oregon
Lines: 15

[]

	"By the way, the KI- and KL-10 processors also reserved a few
	addresses in the I/O space to be "unprivileged". That is, I/O
	instructions (DATAI, DATAO, CONI, CONO) were allowed to these
	few addresses from normal user-mode programs. I'm not sure if
	this was ever used by anyone..."

While we're reminiscing, the KA-10 (first PDP-10 if you don't count the
PDP-6) had "user mode", "monitor (supervisor) mode", and "user I/O
mode".  This last differed from user mode only in that all of those I/O
instructions were available.  I never saw it used, either.

  -=- Andrew Klossner   (decvax!tektronix!tekecs!andrew)       [UUCP]
                        (andrew%tekecs.tek.com@relay.cs.net)   [ARPA]