Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cornell!uw-beaver!rice!sun-spots-request
From: auspex!guy@uunet.uu.net (Guy Harris)
Newsgroups: comp.sys.sun
Subject: Re: Experiences with 386i serial ports under DOS
Keywords: 386i
Message-ID: <1148@auspex.UUCP>
Date: 30 Mar 89 05:14:53 GMT
References: <8902161302.AA02088@cobra.mitre.org>
Sender: usenet@rice.edu
Organization: Auspex Systems, Santa Clara
Lines: 15
Approved: Sun-Spots@rice.edu
Original-Date: 11 Mar 89 00:59:53 GMT
X-Sun-Spots-Digest: Volume 7, Issue 214, message 3 of 13

>Remember that the DOS interrupt handlers aren't really talking to the
>hardware directly - they're going through Unix!

Are they? The 80386 has an "I/O Permission Bit Map" that, I think, lets an
OS allow non-privileged programs (including DOS programs running in a DOS
emulation) directly manipulate *some* devices, while not allowing them to
manipulate *all* devices.  I don't know whether the implementation of
VP/ix on the '386i uses this.  I also don't know whether it allows
non-privileged DOS programs manipulate the serial ports.

However, this *still* doesn't necessarily mean "real-time" interrupt
handling will work well; just because the program can directly bang on the
device with I/O instructions doesn't mean it'll instantly see interrupts
from the device (for instance, what if the interrupt handling code is
paged out, assuming DOS tasks are paged?).