IBM Mainframe Discussion List <[email protected]> wrote on 12/02/2011 05:48:18 PM:
> Am i guaranteed that going into AR mode > and setting a non-zero access register to 2 > gives me access to the HOME address space > through the corresponding GPR, no matter > how many space-switching PCs are stacked > up? > > If the answer to the question is "it depends", > please try to be as clear as possible about > what it depends upon. Every SRB and TCB is dispatched with a Dispatchable Unit Access List (DU-AL) whose entry for ALET 00000002 translates to the dispatched (home) address space. Space switching PCs affect which PASN Access List is current, but they do not change the DU-AL. Here is the "it depends": While processing an I/O interrupt, the interrupt handler switches to an interrupt handler DUCT, which points a special DU-AL where the entry for ALET 00000002 is invalid. So you cannot use 00000002 to access the home space when you are executing in an I/O DIE (Disabled Interrupt Exit) routine. I was going to say that the same is true for external interrupts and Timer DIE routines, but since you have such faith in my accuracy, I though I had better verify that. Well, it was true when access register support was first implemented in SP3.1.0, and remained true through SP4.3.0. But it was changed in SP5.1.0 as part of the support for subspaces. Since SP5.1.0, external interrupt processing remains on the DUCT (and thus DU-AL) at the time of the interrupt, and only switches to the interrupt handler DUCT if the external FLIH returns to the dispatcher instead of returning to the interrupted work unit. Jim Mulder z/OS System Test IBM Corp. Poughkeepsie, NY ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
