my next "spare time" project....

[Mark L. Chang]

In-line, below:

On Wed, 9 May 2001, Marc Swanson wrote:

> > I guess if we went somewhere down the LinuxBIOS and a real-time kernel
> > avenue, it just _might_ work.
>
> I'm not sure you need a real-time os to do it... so long as you aren't doing
> lots of other silly tasks I don't think the important stuff would be swapped
> out of the cpu at a "Bad time".. or at leat all that much anyway ;-)  Even
> changing the nice level of the process(es) might do it.

IMHO, timing is very important. At 5000rpm, you need to handle start,
dwell, and stop on five injectors in sequence for direct-fire. Not a good
time for something to swap in or out. Now, granted, we'll strip this thing
down to its bare essentials, but still, you have no guarantee that the
kernel won't want to be doing something else. Don't get me wrong, you
could give it a shot. I'd try with an RTlinux kernel just to be safe.

> > Otherwise, you have silly issues such as boot time
>
> if I run a flash media storage device, we're talking < 5 seconds.  That's
> less than some hot rods take to prime their fuel pumps.

Yep. Solid-state devices to boot from are nice. LinuxBIOS helps, as does
Bob's "burn to ROM" suggestion. Okay. I'll concede this one.

> this is _linux_ we're talking about here right? :-)
> The only crashing issues I'd be worrying about would be bugs in my softare.
> Memory leaks aren't so bad unless a seg fault/bus error occurs at 100mph!

Well, it can crash. I guess all embedded systems can, so I'll let this one
go as well :>.

> > Plus, standard computer hardware isn't really fit for an all-weather car
> > environment.
>
> so long as the hardware runs someplace nice and dry I don't think that will
> be a problem.  I've seen some pretty cool PC on a chip configurations with
> built in A/D hardware about the size of a PCI card..

True. Really depends on where you live, climate-wise. I'd stick with
Haltech for Chicago winters and summers where condensation, bad roads, and
all that combine for harsh living conditions. But yes, no more than any
other solid-state EFI computer.

You could start by getting a PC104 or Biscuit (Bisquit) PC sized computer.
They should have either a CardBus, PCI, or some other way to hook up an
A/D system and you should be set.

> that's one of the things I've considered.  The most serious issue you've
> raised thus far (and that I've thought about) is no guarantee on processor
> time.  A well crafted simulation will tell me what I need to know in that
> regard.

Well, it would be tough. You would have to simulate how your system
responds to random interruptions that are random in duration. Say, memory
garbage collection by the kernel -- hard to say how long that will take,
or when it will take place. Too long, or at the wrong time, and you
certainly will mis-fire.

Not trying to shoot you down here, because I love Linux in all flavors.
Just trying to keep my eyes open... I'd start with the PC/104 and an A/D
card. Should be fun.

Mark

-- 
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