Date: Wed, 30 Jul 2003 19:50:04 +0100
From: John Bradford <john@grabjohn.com>
Message-Id: <200307301850.h6UIo412000243@81-2-122-30.bradfords.org.uk>
To: john@grabjohn.com, pavel@suse.cz
Subject: Re: PATCH : LEDs - possibly the most pointless kernel subsystem ever
Cc: linux-kernel@vger.kernel.org, pgw99@doc.ic.ac.uk
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1436
Lines: 34

> > > But this kind of blinkenlights needed pretty fast LEDs. (At 486 time
> > > I decided that parport on ISA is fast enough..)
> > 
> > I'll buy some LEDs and build a parallel port connected LED panel
> > tomorrow...  Do you think the overhead of driving the LEDs would have
> > too much of a negative effect on system performance?  If so, or if
> > we
>
> I'm not sure. At 486 days I was pretty sure it did not matter. These
> days you might get 10% slowdown on some microbenchmark, or something
> like that. I do not think it can slow down common tasks.

OK, so no problems there...

> My construction of LED lights is extremely flaky, and I'm afraid of
> burning printer port. At 486 days ports were expected to survive such
> abuse. Not sure if todays EPP/wtf ports can handle that.

This could be a problem, though - now I've looked in to it, the
maximum recommended current drain on the parallel port seems to be
really low :-(.

I've CC'ed Alan - maybe he can offer some advice.

(Alan - basically we're thinking of using this LED-on-parallel-port
driver for a standardised 'front panel', showing things like interrupt
being serviced, BKL taken, etc, for debugging purposes.)

John.
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