Re: [9fans] A shot in the dark

[Digby Tarvin <digbyt@acm.org>]

Don't know where to find that paper, but it reminds of a friend
at UNSW (in Sydney) that used to instrument the OS9 kernel by setting
and clearing bits in the parallel port.

The monitoring hardware was indeed simple - an analogue voltmeter
connected to the bit of interest to produce a simple but effective
short term average.

For example, a bit that is cleared when in the system idle loop
produced a 'tacho' style analogue load meter.

That must have been in the early 80's, but I still find the parallel
interface a good method of getting real-time diagnostics, or front
panel style indicators for statuses such as system/user mode.
Consequently I don't welcome the current trend toward optimising
them out of new hardware. USB parallel interfaces may be ok for
driving printers, but they are no substitute if you want a very low
overhead, low latency i/o mechanism.

Regards,
DigbyT

On Tue, May 27, 2008 at 06:54:58PM -0400, Pietro Gagliardi wrote:
> No, I wasn't around that time :-) But I was looking for the Hello
> World X11 paper a while back, which was pre-website USENIX. But on the
> USENIX website it seems that you can purchase papers from before
> 1991(?). Perhaps they had a paper?
>
> On May 27, 2008, at 6:02 PM, ron minnich wrote:
>
> >OK, this is a long shot, but i'm running out of ideas.
> >
> >Long, long ago, at a Usenix, I saw a talk by some adventurous
> >australians (are there any other kind?). It was concerning some neat
> >hardware designed for kernel monitoring.
> >
> >They had done a very neat hack. Basically, they modified the C
> >compiler so that, on function entry and exit, the code would emit a
> >16-bit quantity to the parallel port. They had some simple hardware to
> >grab the data.
> >
> >WIth this, they were able to get some nice kernel performance numbers,
> >all for the (low at the time) cost of an outw to the parallel port.
> >
> >OK, I have done some searching and can't find this. IIRC it was
> >pre-website usenix. I am going to UCB this week and may have time to
> >hunt it down in the paper archives, but ... just wondering ... anyone
> >else remember this?
> >
> >thanks
> >
> >ron
> >
>

--
Digby R. S. Tarvin                                          digbyt(at)digbyt.com
http://www.digbyt.com