Old 486 Board for ECU??

[Axel Rietschin]

----- Original Message -----
From: "Mike from West Australia" <erazmus at wantree.com.au>
To: <diy_efi at diy-efi.org>
Sent: Tuesday, May 02, 2000 8:10 PM
Subject: Re: Old 486 Board for ECU??


>
> At 06:52 AM 2/5/2000 +0200, "Axel Rietschin"
> <Axel_Rietschin at compuserve.com> wrote:
> >> 1. PWM's are all *low* frequency - easy to handle in software.
> >
> >I've yet to see that. Interrupt activity will screw your timing badly.
>
> No it won't. Because interrupts are synchronous.

???

> And interrupt overhead
> is the same to +- 1 instruction, unless you want a problem with MSDOS.

As far as I know, not all instructions have the same duration on a x86 so
interrupt latency cannot possibly be fixed.

>
> >> 2. Most sedan ECU's do not have water injection, or IC spray
> >
> >Most sedan do not need a reprogrammable ECU either, thinking this way.
>
> What point did you try to make in the first place to bring up the
suggestion
> that a 486 m/b needs to handle water injection and IC spray ?

One of the reasons why I'd consider a custom ECU is to be able to control
more things than the existing ECU already in the car, and one of the reasons
why I'd consider building an ECU is to control more things than the most
sophisticated ECU I can purchase is able to control. Water injection and
intercooler spray are on my wish list, among other things (plenty of ECU
doing just that are available, by the way, but that's a completely different
story).

> >This is where I don't get it. If you read the timer in the ISR, the int
> >frequency gives you the base time increment at which checks are made.
>
> No. That might be how you'd do it - I wouldn't.

I'd use an MPC555 and spend most of my time writing high level engine and
drivetrain control code :)

> See above point. Just use the more common analog AFM's to start with.

You don't always have a choice.

> Nop. Many were variants of 68HC705 devices with timers less complex or
> capable then those on a 486 m/b. The x86 architecture is not a problem,
> why are you so vehement that x86 architecture is a problem.

I don't, really. I just question the feasibility and performance of a PC
ECU.

>
> (Just don't use MSDOS to do all your int processing.)

You keep mentionning MSDOS while I suggested to write the control code on
top of the BIOS, and even to write a special purpose BIOS. Note that I never
attempted to discourage those wanting to run a multitasking, multiuser OS
and also a GUI, next to the EFI code all on the same 486 ;) I'd love to hear
you on that aspect of the 486PC ECU, by the way.

> >> You don't *need* speed to do it,
> >
> >'No matter how fast' was in my very first reply to this thread.
>
> Are you saying a DX4/133 is no better then a 25MHz cpu to handle
interrupts ?

No. But I could be saying saying that a humble 4Mhz PIC (for example) with a
CCP module or two is much better than any x86 PC at generating jitter-free
PWMs or reading a frequency input.

> Nop. Do it in software. You don't *need* a PWM module to turn on an
> injector, check a timer and turn the injector off again - really !

You may not see many PWM sensors/actuators around you but I do. You say you
can do it all in software and I have no reason not to believe you. However,
this will use a lot of your coding energy and a lot more CPU cycles for a
less accurate result compared to hw generated/measured signals. I believe
that if the hw does more for you, you'll have more time to make the sw do
more too.

> Granted I am not talking an overly complex EFI system but a common
> sequential injection ECU function can be done with a 486 m/b, ADC
> and signal conditioning and that applies to most unmodded street cars
> of last 10years.

"semi co marketing" must be pretty good since they successfully convinced
the entire automobile industry to use specially designed components and
systems instead of using inexpensive off the shelf commodities like PCs to
make ECUs ;)  ;)  ;)

I'll watch this thread with great interest, looking forward to hear from
successful 486PC ECU implementations

Regards,
Axel






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