This is what we used to call a Pipe Cleaner in the old days. It caused the CPU pipe to be flushed.
One used to do this to get ready for an interlocking instruction, to make sure that everything in the pipe ahead of this instruction was committed. In certain cases, we followed the instruction that needed this with a Pipe Cleaner as well. I have not read the PoOP at this level for years so I don't even know if that instruction still clears the pipe or not. Or if Out of Order instruction operations would go nutz with it. Regards, Steve Thompson --- [email protected] wrote: From: Melvyn Maltz <[email protected]> To: [email protected] Subject: Is TESTCB a bad boy ? Date: Mon, 26 Oct 2020 11:15:44 -0400 In ancient times it was common practice to do this sort of thing... SWITCH NOP GO MVI SWITCH+1,X'F0' I believe this clears the cache and causes severe performance hits In my research into TESTCB for the z390 Project I found that it dynamically builds the subject instruction for an EX Would this have the same performance hit ? Melvyn Maltz.
