User program

Before issuing a PC instruction, the user's program must:

Save general registers 14 through 12 at the location starting at offset 12 (word 4) in the save area pointed to by general register 13. The program must save registers before issuing a PC instruction because the basic PC linkage updates general registers 3, 4, and 14. As a result of the update, the address space where the save area resides might no longer be the currently addressable address space.
Save the current SASID in bits 16-31 of save area word 5.
Optionally load general registers 0, 1, and 15 as parameter registers.
Load general register 2 with the PC number.
Issue the PC instruction specifying general register 2.

When the PC routine returns control to the user's program, the user's program must restore its general registers and its secondary address space identifier (SASID).