Register conventions

SVC routines are entered with the following data in the general purpose registers:

• Registers 0, 1, 13, and 15 – Contents when the SVC instruction was processed.
• Register 3 – Address of the CVT.
• Register 4 – Address of the TCB.
• Register 5 – Address of the current RB (for type 1 or type 6 SVC), or address of the SVRB for SVC routine (for type 2, 3, or 4 SVC).
• Register 6 – Address of the SVC routine entry point.
• Register 7 – Address of the ASCB.
• Register 14 – Return address.
• Other registers – Unpredictable.