[Diy_efi] PC-laptop based efi

[Brian Dessent]

peterw wrote:
> 
> > Hi, i'm looking into the possibility of designing a efi control system
> that
> > would run on a laptop. I think that it would be of the multi-port variety.

> Speed and timing may bring you undone. In order to read sensors, lookup
> tables, do calculations you will need a fast machine running a true real
> time operating system, especially if you are doing lookups and calcs every
> rev or every second rev. At 10,000RPM a rev takes about 6 milliseconds. This
> may fine on a fast machine untill the OS wants to flush the disk cache or do
> some other such system thing. Note Windows and Linux are not real time

I agree, you will pull your hair out trying to do this purely with a
PC-like design.  You will make your life much harder by having all the
time critical stuff percolate all the way up to the CPU.  At the very
least you would want to run some custom bastardized FreeDOS or something
running one big honkin' polling loop.  FORGET running Windows, it's out
of the question.  RTLinux or QNX may be possible candidates thoough.

The way I would suggest going about this is the divide and conquer
method.  Build a few independent modules that do all the timing-critical
functions such as spark timing and injection events (after all, you'd
want this beast to be full sequential I'd imagine.)  These sub-systems
wouldn't need to know anything about enrichment stragies or maps of any
kind, let those higher level decisions happen at the CPU level where
they are not as time critial.  It sounds like the Ford EDIS-4/6/8 is a
perfect example of this kind of implementation, and probably the reason
why Bowling and Grippo are into it for Megajolt.

If you do this right you still retain all the advantages of a PC --
mature, robust tools for development, logging, visualizing -- while
still having the advange of most of the time sensitive tasks offloaded
onto dedicated hardware.   I'd be a little worried about relying on a
laptop or PC-104 chassis as the main ECU, I mean think of all the "my
disk crashed and I was trying to run SCANDISK, officer!" jokes you could
make.  All in all I'd say attack it more from the standpoint of "how
could I build or modify an existing ECU so that it's in constant
communication with the PC, with all internal variables exposed and
accessable", rather than trying to bring the PC down to the level of the
microcontroller.

Brian
(of course I've never actually done any of this, but I've been down the
same "wouldn't it be neat" trail of thought a million times...)

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