If the control of PERCON is transferred to a user module, the contents of registers 1, 13, 14 and 15 have the following meanings:
Register 1: | Contains the address of a sequence of 4-byte address constants indicating parameter areas. The number of parameter areas varies depending on the interface. The end of the address list is indicated by a constant in the form X’80000000’. |
Register 13: | Using this register PERCON transfers the address of an 18-word save area to the user module. In this area the PERCON registers are to be saved by means of the SAVE macro, which must be issued at the beginning of the user routine. By means of the RETRN macro (see the manual [8] "Executive Macros") control can be returned to PERCON. With the help of the save area the RETRN macro can also reconstruct the contents of the PERCON registers. For this reason register 13 must not be overwritten by the user or must be reconstructed before RETRN is called. |
Register 14: | Return address. |
Register 15: | Branch address of the user routine. |