🚀 go-pugleaf

In article <910524.224442.EDT.VALDIS@vtvm1.cc.vt.edu>, Valdis Kletnieks
<VALDIS@VTVM1.CC.VT.EDU> says:
>Does anybody out there have a war story of a "undocumented" opcode or
>similar feature on an IBM 360/370/etc mainframe?

Well,  this is  probably more  appropriate for  the alt.computer.folklore
newsgroup, but here goes. Back in the early 80's I worked for a small PCM
called Magnuson. The Magnuson processor  had been designed by Carl Amdahl
(which meant  our company was called  "Son of Amdahl") and  competed with
the 138/148 (and later the 4331/4341) boxes.

The guy who wrote the initial cut  of the microcode was a guy named Kevin
Anderson  (still in  jail, last  I heard,  for trying  to ship  things he
shouldn't have to the Russians). Kevin  was an Othello buff, and hacked a
game  we had  on  our games  disk... moving  critical  routines into  the
microcode. The Magnuson  M80 was, therefore, the only  IBM 370-compatible
machine that had (in addition to ECPS:MVS, ECPS:VM, etc.) an undocumented
ECPS:OTHELLO.

I pity the poor programmer who stumbled into that instruction.  :-)

Speaking of  assembler trivia,  what are  the three  370/390 instructions
that have to be done twice in microcode for each target instruction? (The
microcode has  to run through the  whole operation once to  see what will
happen, and then again for real.)

Hint: The answer's in the POO.  :-)
---
Jim McIntosh (jim@auvm.auvm.edu)
The American University
Washington DC 20016-8019 USA