UAEFI: two low tooth count VR triggers

[Dron_Gus]

I (steal) rented (form new owner) my old Subaru GC8. https://rusefi.com/forum/viewtopic.php?t=2023 . BTW another 5 years almost passed.
I wanted to run some LTFT test on it.
I wanted to run bleeding edge uaefi on it. It was running MRE 5 years ago. It is still good but no WBO, no EGT...
So I did an "adapter" to stock ecu connector.

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I knew that I will fall into MAX9924 watchdog issue.

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But there is not way to swap cam or crank sensor to Hall or even swap trigger wheel to something more toothed.
Owner of this car likes his Mines ECU a lot. And he does not believe in my tuning skills a lot.
So no permanent swap to RE is possible, car should be reverted back to original state by reconnecting ECU.

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So I have to dig a little into MAX9924 documentation.

Problem statement:
MAX9924 does not like low-tooth count trigger wheels because of its "adaptive peak threshold" and its watchdog.

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Adaptive peak threshold is enabled in A1 and A2 modes. But what about other modes?

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B mode looks what I need. But it needs externally supplied Bias and Threshold voltages. (Why did Maxim decided disabling internal Vref it this mode???)

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This mode is exactly what we need. Zero crossing feature is still enable, but we can supply external threshold voltage.
So MAX9924 uses Ext threshold voltage when signal goes up and uses Bias voltage as threshold when signals goes low.
Cool thing is that uaEFI already have source for both voltages in Discrete VR circuit.

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Solution:
According to mode table what we need to do to switch from A2 to B mode:
1. pin 6: ZERO_EN connect to VCC instead of GND.
2. pin 4: supply 2.5 V instead of GND
3. pin 8: EXT, supply external threshold voltage

Pins 4 and 6 needs to be lifted from PCB to be disconnected from GND.
Pin 8 initially is not connected to any circuit.
I used hot air gun to de-solder whole chip. Then I twist pins 4 and 6 up so both do not touch PCB when I solder it back. And then I solder chip back.
Now use thin wire to connect:
1. pin 6 to pin 10 of the same chip.
2. pin 4 to Vref at R769 + C754. See file:///home/work/rusefi/docs/uaefi-d-ibom.html for its locations
3. pin 8 to thresh_high at U756 pin 1. See file:///home/work/rusefi/docs/uaefi-d-ibom.html for its locations

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Results:
I was finally able to rev up to red zone without trigger issue.
Also trigger signal looks perfect, even on high rev.

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