Re: [9fans] A shot in the dark

[Paul Lalonde <plalonde@telus.net>]

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FWIW, we used a similar technique just last summer debugging some PS3
code.  The dev system is kind enough to include 4 front panel lights
and a very lightweight API for setting them.  We wound up "printing"
out the program counter during a deadlock by mashing too many calls
to set the lights into the suspect areas.

I miss hardware debuggers.

Paul

On May 27, 2008, at 5:06 PM, Digby Tarvin wrote:

> 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
>

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