Coding guidelines documentation

docs/ARCHITECTURE.md

@@ -21,9 +21,10 @@ As mentioned previously, all core engine control is handled on the Cortex M7, th
 
 ### Input Signals
 The engine provides two key input signals:
-- Crank pulse
-- Cam pulse
+- Crank pulse, triggered every 180 deg
+- Cam pulse, triggered every 720 deg and slightly dephased
 These are both registered using a hardware interrupt using `TIM2` as a low jitter time source.
+These signals can have missing pulses or extra triggers which need to be accounted for.
 
 ### Time Base
 `TIM2` is the main timebase used to control the engine, it provides 4 channels that are used as follows: