These registers are used in function call and return:
A0..An In full call, the first three arguments. In unknown values return, the first three return values.
CFP The current frame pointer. In full call, this initially points to a partial frame large enough to hold the passed stack arguments (zero-length if none).
CSP The current control stack top pointer.
OCFP In full call, the passing location for the frame to return to.
In unknown-values return of other than one value, the pointer to returned stack values. In such a return, OCFP is always initialized to point to the frame returned from, even when no stack values are returned. This allows OCFP to be used to restore CSP.
LRA In full call, the passing location for the return PC.
NARGS In full call, the number of arguments passed. In unknown-values return of other than one value, the number of values returned.