Long ago in a galaxy far away, IBM introduced the concept of resumeable
instructions; an interrupt could occur in the middle of the instruction
execution and the instruction would continue properly after a normal
dispatch. It appears that CLCL and MVCL were not only the first such long
instructions but also the last. Subsequent long instructions have required
testing the condition code to see whether the instruction had been
interrupted in media res. Superficially that seems like extraneous
overhead. Can anybody cast any light on why IBM went that way?
--
Shmuel (Seymour J.) Metz, SysProg and JOAT
ISO position; see <http://patriot.net/~shmuel/resume/brief.html>
We don't care. We don't have to care, we're Congress.
(S877: The Shut up and Eat Your spam act of 2003)
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