[Diy_efi] PC-laptop based efi

[Brian Dessent]

Marcell Gal wrote:

> yes, a PC can be programmed like a microcontroller. IIRC today's
> PC's have the timing interrupt capability that is sufficient for an
> eventqueue. (And they have precision timers, so under
> 1ms timing-precision is clearly achievable).
> 
> But you rarely operate your CNC under -20C temperature, and
> shake the house under operation like a vehicle shakes.
> Notebooks might be perfect for amusement and non-critical
> displays (maps, mileage-statistics, tuning etc..) but why would you
> put essential tasks on them, when you can put those functions
> to an uC for $2 extra? (compared to a little more dummy uCs
> that can only do the TPU  - Time Processing Unit - functions)

Yeah, while you could coax the functionality out of a general-purpose
CPU, you'd lose all the properties that make it really useful, namely
the ability to use all that software out there.  You would have to run
either a very barebones OS, or a regular OS with a lot of hacking to
ensure that the controller app has complete and timely access to all the
interrupts it needs.  In such a state you would not be able to, e.g.,
bring up Excel to make a nice purdy display of your fueling map.  In
fact I don't think you'd be able to run much of anything else except
this dedicated task loop, at least while it's actively controlling the
engine.  

On a NT/XP system, try putting a process that's actively doing something
at the highest priority level ("realtime") and watch the rest of the
system fall completely to its knees.  You'll have the pleasure of
clicking the mouse or pressing a key and getting your response a few
seconds later, and watching as the display turns into a big mess as
those UI threads that normally repaint the screen when it needs updating
just aren't getting any timeslices.  

With very careful design I suppose you could mitigate this effect but
the point I'm trying to make is that using a regular computer as a
real-time controller makes it no longer a regular computer, and you
can't use it like one.

Brian

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