User in Primary Mode

A user program that's running in primary mode can invoke a PC routine that receives control in either primary mode or AR mode. Any addresses that the user program passes must be located within the user's primary address space. The user must not use ARs to pass parameter values or addresses. Before issuing a PC instruction, the user must:

Load the PC number into general register 14.
If there is a parameter list to pass, load its address into general register 1.

When the PC routine returns control, GPRs 2 - 13 and ARs 2 - 13 are restored to their original values. GPRs 0, 1, and 15, and ARs 0, 1, and 15 contain the values that were in them when the PC routine issued the PR instruction. GPR 14 and AR 14 are used as work registers by the system.