You can use the Supervisor Call (SVC) instruction to enter Supervisor mode, usually to request a particular supervisor function. The SVC handler reads the opcode to extract the SVC function number. A SVC handler returns by executing the following instruction, irrespective of the processor operating state:

MOVS PC, R14_svc

This action restores the PC and CPSR, and returns to the instruction following the SVC. IRQs are disabled when a software interrupt occurs.