> -----Ursprungligt meddelande----- > Från: IBM Mainframe Assembler List [mailto:ASSEMBLER- > [email protected]] För Chris Craddock > Skickat: den 6 januari 2012 17:45 > Till: [email protected] > Ämne: Re: z/Arch design question. > > > My curiosity is why MVCLE sets the CC, thus forcing user code to branch > back. Why not just not update the PSW instruction address until all the > data is processed? Still allow the interrupt like MVCL does, of course. I > understand why the interrupt is necessary, especially in a single CP > environment. Does anybody know? Is it a "millicode" thing? > > > Well it *is* a millicode "thing" in so far as the instruction is > implemented in millicode. So why does it work this way? The idea is that > the instruction can come up for air somewhere in the middle and give the > application the opportunity to do something else before > continuing/resuming the move. Examples would be (perhaps) checking I/O > completion, kicking off (another) I/O request, processing some business > logic on the data being moved etc. Can't say I have ever come across a > situation where that actually happens. But they are at least theoretically > possible with MVCLE and *not* with the plain old fashioned MVCL. > Realistically the only time that this would come into play is while doing > very large moves on a busy system. Otherwise the MVCLE just does its thing > and control passes to the next instruction. > CC >
I imagine MVCLE been used when handling linear datasets (VSAM) in memory. Regards, Thomas Berg _________________________________________ Thomas Berg Specialist A M SWEDBANK
