Paul,

With the Parallel Port, you are going through the super IO
Chip.  This device is off the LPC (low pin count) bus.
Four lines with multiplexing of command, address, and data
bits.  From the LPC back into the system are a few more
paths.  While the printer will generate an interrupt, that
interrupt is polled to see if it is set.

The BIOS is running a bunch of events in the background,
with DOS sitting on top of that software.

System is not deterministic.  So there is variable timing
to the system on what the parallel port is serviced.

There are ways of working around this, from both hardware
and software points of view.  For hardware using a separate
timing subsection to handle inputs from the eccentric shaft
pulley, to software of rewriting the bios and coding
everything in a fixed matter.  So it can be done.

Nice thing about rotary engines is they are so much simpler
to determine when to fire injectors, and spark plugs.  No
camshaft timing required, so using the Ford Ignition
subsystem for spark and DOS computer for fuel is very
viable, that it should work nicely for the dyno testing.
Once you have the parameters established, then code in that
small micro controller for aviation use.  I still like
redundant back up with 'Notlauf' (emergency run, aka limp
home mode) which the 555 timer could provide.

Tom W

Good info Tom. Thanks. That explains why MTIMER is all over
the playing field. I can buy a PCI plug in card with an external
counter timer chip which may improve the situation. Also do
you think a PCI plug in par. port card would help. I have one so
I will try that.

I have a listing around here someplace for the IBM BIOS.
You would not happen to have it in computer readable form
would you? How about a list of the back ground processes?
I know time is lost to refresh the ram.

Is there anything I can disable in the BIOS setting or config.sys?

I don't think recoding the BIOS will work on these cheap mother boards
as the ROM appears to be embedded  in one of just several chips
on board. I might be able to live with it as is if I can get
the RPM with a external counter timer chip.

Thanks again for your thoughts on this thing.

------------------------------------------------------------------------
http://www.via.com.tw/en/products/mainboards/others/p4pb_ultra.jsp

I think I was wrong about changing the BIOS. It appears
to be in flash. Perhaps they have a real time BIOS.

There are two ways to update the BIOS:

Second method:
(System needs to boot into DOS prompt with bootable disk):

1. Make a bootable system 3.5" diskette.
2. Then copy the flash utility (eg. awfl818.exe) and the new BIOS file (eg. P4XBSOLI.BIN)
onto this diskette. The latest BIOS update and flash utility can be downloaded from
www.viavpsd.com for your specific product.
3. Boot the computer using this diskette.
4. At the A:> prompt type awfl818.exe (file name).BIN.

You can find out additional parameters of the flash program by type "awfl818/?". This will
cause the flash utility to load and automatically use the new file. Just follow the
prompts that you see on the screen. When you are through, reboot your computer. Please
load the optimized default settings in the BIOS.

WARNING!! During the final flash process, power should not be disconnected and the process
should not be interrupted or the motherboard will not be able to boot up.

I am looking into this further.

---------------------------------------------------------------
I have email into VIA. They make a whole range of PC boards for
embedded applications. If every car had a PC the possibilities
are stunning.

http://www.via.com.tw/en/company/locations.jsp#usa

BASIC is the fastest way to program. Programs can be written in
minutes that take hours or days in C or assemble language.

This mother board is 200 times!! TWO HUNDRED TIMES!!! faster than
boards just ten years ago. BASIC historically has been dismissed
as too slow for real time applications. NOT TRUE ANYMORE.
DOS BASIC instructions execute in less than one microsecond.

Paul Lamar