On 1/6/2012 8:24 AM, McKown, John wrote:
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?
It is a chip "real estate" thing. The amount of extra silicon used to make an instruction interruptible is extreme. It is a complex undertaking. Using standard, non-interruptible instructions is simpler and allows many more new and useful instructions to be added to the instruction set. -- Edward E Jaffe Phoenix Software International, Inc 831 Parkview Drive North El Segundo, CA 90245 310-338-0400 x318 [email protected] http://www.phoenixsoftware.com/
