Hi Bernie,
Not enough free context could be detected by the context management subsystem and result in the FCD / FCU trap.
FCD occurs when FCX points to LCX. LCX is a user chosen free element typically chosen close to the last free element of the CSA limit. This means that the free context list is 'almost empty'. The operation responsible for the context save completes normally and then the FCD trap is taken. The FCD trap handler is normally expected to take some form of action to rectify the context list depletion
FCU, on the hand, occurs when the FCX=null, meaning that the free context list is empty and the system cannot perform a context switch properly. This means that the architectural state is lost, and the occurrence of an FCU trap is a non-recoverable system error, which means that the user should ultimately initiate a system reset.
See 6.3.4 Context Management (Trap Class 3) of the architecture manual for details.
Best regards,
Mr. AURIX™
