-----Original Message----- From: IBM Mainframe Discussion List [mailto:[EMAIL PROTECTED] On Behalf Of Jim Mulder Sent: Thursday, November 08, 2007 6:07 PM To: [email protected] Subject: Re: CSA 'above the bar'
IBM Mainframe Discussion List <[email protected]> wrote on 11/08/2007 06:23:58 PM: <SNIP> Actually, no. We are talking about virtual addressability, and x'000000' is certainly addressable as a 24-bit virtual address in every address space, and addresses the PSA for the processor on which the code is executing. Furthermore, absolute frame 0 is also addressable by using the SQA virtual address of the PSA for the processor on which the code is executing. This will reverse prefix to absolute 0. As of z/OS 1.5, if there was more than one CPU available at IPL time, the SQA virtual address of the a PSA will be a 31-bit ESQA address. Otherwise, it will be a 24-bit SQA address. As of MVS/XA, we always use a non-zero prefix for each online CPU, so practically speaking, MVS does not use frame absolute 0 for anything other than IPL processing and SADMP processing (SADMP only uses one CPU and uses a prefix of zero). <SNIP> You did say dedicated. And it certainly appears to me to be both dedicated and reserved (by architectural definition). In the MVS world, if a Problem State program attempts to modify 00000xxx (where x is 0-512 decimal and regardless of the content of the current base register) and LAP is on... So it is not truly available (except to the SCP). Otherwise, as I recall [MVS environments], that page is Key0 non-fetch protected. [The above is only for non-Z architected machines. I honestly haven't read the requisite chapters in the new PoOP.] Regards, Steve Thompson -- All opinions expressed by me are my own and may not necessarily reflect those of my employer. -- ---------------------------------------------------------------------- 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
