VAX Complex Instructions
note that the ficon description is nearly identical to the HYPERChannel remote device adapters (A51x) boxes starting...
Version 0.1 of vtapeutils is available from the Sourceforge project page at vtapeutils is intended to ba a package of utilities to work with virtual tape files. Although the current program is not structured this...
I worked for many years on VAXen and while I never wrote anything in its buttembly language (Macro) I got to read it a lot and became quite familiar with it.
For those who never encountered them, the VAX was a byte machine 'til it hurt with a remarkably complex instruction set. It had a POLY instruction for polynomials, another for calculating CRCs etc. It had 5 operand byte instructions including one which was obviously to implement a Cobol EXAMINE statement in one instruction.
The thing that puzzled me was a SYSGEN parameter, name long since forgotten, which set the smallest size(in pages) a working set could be reduced to. The idea was to stop working sets getting smaller than the number of pages a single instruction could access, and thus page fault itself to rest.
The book said the maximum was 54 but I could never work out how. Even if the instruction crossed a page boundary and all of its five indirect operands crossed two page boundaries and everything else I could think of, I could only get to about half that.
Any wise souls out there know how?
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