I'll try and summarize what has been discussed to and from regarding the nissan trigger system.
First, we need to understand how the current trigger works.
It's an optical system located on the cam. There are two sensors. One of them records the engine speed using 360 small slots. The other one triggers the ignition events using different sized slots. It knows which cylinder is 'active' by counting the number of small slots while the larger slot is open. See [this image] and reread the paragraph and it will make sense.
![[this image]](http://200sx.jagenheim.se/images/trigger.png){kind=link}
This image is for the CA18DET engine. The SR20DET, RB26DETT and the other nissan engines works in exactly the same way, but differs on where the slots are placed and the number of cylinders.
Update: this may not be true. I've seen pictures of discs where only one of the slots is large (to indicate #1) and the rest is small. If someone could find a trigger disc which isn't from a CA18DET to confirm this, it'd be great. It's not a big problem, but it will affect the implementation.
So, how do we support this in VEMS?
360 camtooth (180 teeth per crank rotation) is suitable for interrupt processing. Especially with the small trick to disable the interrupt for the dense teeth where not needed (neglected 95% of the time).
There is an implemenation for this in SVN now; but we need to stabilize trunk before merging it in.