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Re: [Gnucap-devel] System simulation

From: Thomas Lundin
Subject: Re: [Gnucap-devel] System simulation
Date: Mon, 19 Mar 2007 18:53:40 +0100

Hi Scott,

> KTechLab implements a system simulator... sort of. It's not a full blown
> extensible simulator like gnucap but it does combine Microcontroller
> simulation with analog simulation. For the microcontroller simulation,
> KTechLab uses gpsim.
It seams like KtechLab has hibernated. The site is down and according to
Wikipedia it sounds rather final. The sources are laying around so I can
try it but I'm a bit hesitant to before I know if its maintained or not.
Pity, sounds very promising.

> Since both gpsim and gnucap support a concept of plugins then
> theoretically one could be plugged into the other. I don't know exactly
> how gnucap implements the simulation model, but I'm certain it's different
> than gpsim! So there would have to be some work to merge the two.

My though was that it looked fairly easy, that most work done in both
gnucap and any MCU simulator with I/O control. You can already run
gnucap for a MCU clockcyle, probe all the inputs then go another clock
cycle and probe again. 
To me it looks like a way to arbitrarily set a digital output in gnucap
would be the only gnucap work, and some interface code in the MCU sim to
fetch and set the I/O pins through a simple pipe. 


> My system simulations are tailored to firmware development. There are many
> things that I can test and develop in a simulation environment. For
> example, I've created behavioral models of the RF ID transmitters. I can
> instantiate these in a gpsim simulation and evaluate how well my RF
> receiver can tolerate a variety of corner case anomalies like slow
> transmitter clocks, single bit errors, bit burst errors, etc. At the same
> time I can simulate switches, and LCD display, LEDs, an RS232 interface,
> etc. My gpsim configuration script is a couple hundred lines long
> sometimes! But I've uncovered all sorts of weird bugs over the last few
> years that would have been extremely difficult to capture with just an ICD
> (or with MPLAB).

This is what exactly what I'm looking. Both running the full system
interactively and being able to set up a test-bench and sweep a number
of parameters to catch those strange parameter-combination bugs that
appear way to often. Let it be that it has to run over night when the
number of parameters increases.

> There are times I've wish gpsim had an even more accurate analog
> simulator. For example, the sort of sigma delta style 1-pin A2D converter
> found:
> If gpsim had accurate I/O pin models then I could better predict the
> behavior of this example. Furthermore I could possibly optimize it and
> evaluate it over corner cases.

I can imagine that you get quite far with what you've done in gpsim (was
quite some time since I used it in a project), and it's a huge
improvement to just software simulation. But I also see a lot cases that
would require more accurate analog simulation. 


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