Re: [Gnucap-devel] System simulation

[Thomas Lundin]

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. 

snip!

> 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:
> 
> http://www.dattalo.com/technical/software/software.php
> http://www.dattalo.com/technical/software/pic/a2d.asm
> 
> 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. 

Thomas