Gentlefolk,
One way to provide high integrity thrust reverse systems is to ensure that no one computer has all controls in its power.
Role [1] of the EIU is to take aircraft power and switch 28Vdc to the FADEC as required - as Flappo post #2.
Role [2] of the EIU is to take aircraft power and switch 28Vdc to the TR Isolation Valve solenoid, when required for Thrust Reverse operation.
Role [3] of the FADEC is to close the TR Isolation Valve solenoid circuit, when required for Thrust Reverse operation. N.B. the FADEC must not* power this circuit from either the 28Vdc EIU supply or from its dedicated generator systems.
Role [4] of the FADEC is to electrically power and actuate other TR valves, when required for Thrust Reverse operation.
* This particular electrical power isolation may have a permissible failure rate; the details are another story.
The combination of the above roles ensure that a TR system could only deploy with concurrent EIU and FADEC command.
I therefore speculate that the reason for the ECAM warning correlation between FADEC and TR operation, is due to electrical supply fault detection/reporting for these 28Vdc buses having shared hardware insdie the EIU.
0'n'1