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From: cet1@cl.cam.ac.uk (C.E. Thompson)
Newsgroups: comp.lang.asm370
Subject: Storing into the CAW (was: (none))
Message-ID: <1364@scaup.cl.cam.ac.uk>
Date: 20 Oct 89 14:56:23 GMT
References: <8910181519.AA05760@brazos.rice.edu>
Sender: news@cl.cam.ac.uk
Reply-To: cet1@cl.cam.ac.uk (C.E. Thompson)
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Organization: U of Cambridge Comp Lab, UK
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In article <8910181519.AA05760@brazos.rice.edu> 
PERSHNG@YKTVMH.BITNET ("John A. Pershing Jr.") writes
>CMS normally runs all programs in (virtual) Supervisor State -- if you
>find that you are in problem state, then there is something amiss.
>
>However, to try to keep you from shooting yourself in the foot, CMS
>protects its own storage areas with a Storage Key of x'F', and sets all
>"user" pages to a Key of x'E'.  This is probably why you are having
>difficulty storing into the CAW.  There are a number of ways to get
>around this annoying behavior ...

All of which he gives correctly. However, there is another point to
keep in mind: doing your own I/O instructions, and relying on things
like the CAW, is going to stop working when (if) you have an XA mode
virtual machine. It is better, where possible, to use the synchronous
I/O diagnose instructions.

Chris Thompson
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