Autopilot calculations

I have the following Raymarine instruments

One S1 SmartPilot, E15016 w/ fluxgate compass
Two SmartPilot Controllers, one ST8001 and one ST8002
One E120 Chartplotter
One RS130 GPS

Both controllers are connected to the SmartPilot via SeaTalk.
The fluxgate compass is connected to the SmartPilot via its dedicated terminals.
The Chartplotter’s NMEA 0183 output is connected to the Autopilot’s NMEA 0183 input.
The GPS is connected to the Chartplotter via SeaTalkng.

The system works well.

Which of the units calculates the new heading when the chartplotter advances to a new waypoint?

Which unit calculates the crosstrack error?

Which unit adjusts the heading to reduce the crosstrack error?

Thank you