gtpm1m1qTPF V4R1 Migration Guide: 3.1 to 4.1

Changing the System State

Use of the set system mask (SSM) instruction will cause problems with both the dynamic address translation (DAT) facility and the program event recording (PER) trace facility. To avoid these problems, replace SSM instructions with the new $MASKC macro to change PSW system masks for I/O, external, DAT facility, and PER trace facility interrupts.