Which computer controls auto thrust on an Airbus A320? An Airbus A320 has seven computers that control flight surfaces:
two ELAC, three SEC, two FAC, and two AP (autopilot) computers.

Is there an separate computer that controls auto thrust, or is this controlled through one of the above?
More specifically on your question:

See diagram below:



In the autothrust mode (A/THR function active), the FMGC computes the thrust, which is limited to the value corresponding to the thrust lever position (unless the alpha-floor mode is activated).




  So as you can see computers/controllers that control the A/THR are:
  
  
  FCU
  FMGC/S
  EIU or EEC
  FADEC
  ADR
  


The **speed or Mach target may be:


  ‐ Selected on the FCU by the flight crew
  
  ‐ Managed by the FMGC.


EPR mode is the normal mode to control the thrust. The required EPR is set by controlling the fuel flow.

DSC-70-35-20 P 1/2

The FADEC has two mode of power setting, EPR and N1 modes.
The FADEC computes the command EPR as a function of : 

‐ Thrust Lever Angle (TLA)

‐ Altitude

‐ Mach number

‐ Ambient temperature

‐ Air inlet total temperature (T2) ‐ Service bleed.

Arming conditions of the A/THR are numerous. The following is a list of the most important ones:

‐ One FMGC operative

‐ One FAC operative

‐ Two ADIRS operative

‐ Two FADECs operative

‐ One channel of the FCU operative

‐ One LGCIU operative

‐ A/THR is not manually disabled (instinctive disconnect pb has not been pressed for more than 15 s).


  So to summarise:
  FMGS computes the THR and the FADEC computes EPR and through EIU/EEC and ECU commands the fuel flow to the engines in order
  to give the desired EPR.