> You can rely on MVCL to operate the way the POP says it will. My impression from reading the POP is that the MVCL is an interruptible instruction so if you're coding first level on a multi processor configuration without an operating system to manager things for you the results of the MVCL can be erractic in appearance even if the instruction has done exactly what it was supposed to since another thread on another processor was updating the storage the MVCL was operating on.
I haven't dug this piece of PoP out for some time, but memory suggests that the interruptibility of MVCL has little to do with it, apart from increasing the window. Even instructions like MVC can cause garbling if two sharing processors hit the same piece of storage at the same time. Older machines used to store a doubleword at a time - do modern designs do a conceptual full-length store at one time? ISTR PoP saying the results of two processors trying to update the same storage at the same time would always be unpredictable. -- Phil Payne http://www.isham-research.com +44 7785 302 803
