Software Design Spec

Combustion Pressure Monitoring Subsystem Software Design Specification

Inputs:

• Crankshaft Position (Frequency Signal - Interrupt Based)

• Engine Load (Analogue signal – ADC)

• Spark Gap Ion Current (Analogue signal – ADC)
  
  

Outputs:

• Optimum ignition timing referenced with engine load and RPM.
  
  

Software Components:

Crankshaft Position Sensor Decoder

• Takes input from crankshaft position sensor via input capture.
• Uses crankshaft position sensor input to constantly update engine RPM and crankshaft position.

Angular Event Generation

• Uses engine RPM and crankshaft position inputs to calculate reference tooth and timing variables for output compare to trigger asynchronous events.

• Steps through each event which has not been carried out this cycle to update timing variables.

Angular Event Sorting

• Steps through all current events and determines which event is next in queue for triggering.
• Next event is assigned to an output compare module.
• Output compare becomes active when the next event reference tooth is reached.

Angular Event Triggering

• Output compare calls event at predetermined time to achieve correct phase.

Ion Current Sampling

• Creates asynchronous events to log samples of the spark gap ion current from the ADC module.
• Creates and maintains buffers, pointers and variables to store samples for later use.

Peak Cylinder Pressure Point Calculation

• Operates on the stored ADC samples to determine the crankshaft angle where peak cylinder pressure occurs.
• The results are stored with reference to the engine RPM and load to allow the ECU to update the ignition timing maps.

Timing information transmission

• The stored results are transmitted to the ECU via UART, CAN, SPI?