----- Original Message -----
From: "Peter Schuller" <[EMAIL PROTECTED]>
To: "Matthew Emmerton" <[EMAIL PROTECTED]>
Sent: Tuesday, March 23, 2004 15:54
Subject: Re: disconnecting keyboard: big trouble !?!

> On Tuesday 23 March 2004 19.44, Matthew Emmerton wrote:
> > FreeBSD should not be working around user's bad practices.
> > It has *always* been a bad idea to hot-plug PS/2 peripherals, and
> > until USB is the norm, will continue to be the case.
> Again I've never heard of anyone running into any kind of problems
due to
> this. And someone else recently posted about not being able to find
> conclusive information on this info at all while googling. So really
I don't
> consider it bad practice at all, since I have never heard of a
failure, nor
> seen any concrete evidence why it would actually be bad.
> --
> / Peter Schuller, InfiDyne Technologies HB


I wasn't to post further to this to the list as it is not FreeBSD
related, but it seems to be of community interest.
Why is PS/2 different from USB? Leaving aside the different physical
and electronic designs, the USB spec calls for hotplugging, and the
PS/2 spec doesn't. The PS/2 IO spec, written in 1986-87 as part of
IBM's Micro Channel architecture, doesn't mention hotplugging all. It
probably never occurred to the original engineers that someone would
try it. (Ever see a spark when plugging something into a wall socket?)
Interestingly, every operating system I've used since PS/2 came on the
market either had no way to detect a PS/2 device was hotplugged, or it
was disabled by default. I believe that's for a reason.
As always, whenever there is a blank spot in a spec, different
companies fill it in differently, so too with PS/2 controllers. Here
is what I have witnessed first-hand happen when hotplugging: works
perfectly, fails to recognize the keyboard without power cycling,
fails to recognize both the keyboard and mouse because they were in
the "wrong" ports, and of course blows the MB.  Also, just because it
worked on one particular MB, don't assume that make and model is
"safe." As I commented off-list, a likely scenario is Brand X buys its
components from various suppliers that have various brands with
various models within brands with various revisions within models;
each of which may or may not support hotplugging.
Ultimately, the question is, what will the particular controller on
the motherboard in the box in front of you do when you hotplug it? Two
methods exist for finding out: the smoke test (pull the plugs, put
them back in, wait for smoke) and o-scoping the ports. Because I don't
care for smoke tests and don't usually have a scope handy, I power
down. Is it a hassle? Oh yeah, but not as big a hassle as replacing a
MB in a box at a colo or datacenter or my desk at home, for that
For those with a perverse sense of humor, IBM has "extended" the PS/2
spec for optical mice, etc. but has not added hotplugging. The
perverse part? You can hotplug some of their product lines. But you
didn't hear that from me ;).



[EMAIL PROTECTED] mailing list
To unsubscribe, send any mail to "[EMAIL PROTECTED]"

Reply via email to