Start/stop with the same Keypad-button?

We have had a few requests for this feature, but i have not yet found a suitable configuration that is safe. The problem is quite complex, even though it seems relatively simple.

First, i think it is better to use an 'Engine running' flag from the ECU rather than guessing if the engine is running based on the RPM (or use both).

In theory, the order of operations would be -

First start the PDM.

Then use a keypad button to enable the ECU, injectors, coils, fuel pump etc.

Then press the start/stop button to crank the engine.

Then once the engine is running (using the engine running flag from the ECU), you can press the button again to disable the ECU, injectors, Coils, Fuel pump etc.

Things to avoid are -

engaging the starter motor when the engine is running. You need to think about what if you press the start/stop button to stop the engine, and then accidentally press the button again while the engine is still spinning. Checks need to be made that the engine has stopped spinning before you can re-engage the starter motor.

having the start/stop button not actually switch off the engine. There needs to be a cut off if the 'engine running flag' CAN Input times out. I also worry about the ECU sending the engine running flag as 'Off', even if the engine is still running - this would screw all the logic up on the PDM side.

I will keep thinking of a way to do it that is robust and safe. If i come up with a way, i will let you know and post it here.