> Ah! I am starting to understand. Leap Second steering is accomplished with > the PTFF instruction and is independent of CVTLSO. PTFF appears to slow down > the physical clock. > > So ... steering and CVTLSO are essentially alternatives, right? CVTLSO > should not include any leap seconds that were previously (or were about to > be) "steered" -- is that right? And if a shop is using STP it is probably > not modifying CVTLSO: CVTLSO is probably either zero, or at least stable. Am > I getting this right? > > Charles
No, you have it wrong. Steering has nothing to do with leap seconds. STP checks the external time source (ETS) at regular intervals and makes adjustments via steering to keep accurate with the ETS. It just so happens that if you don't schedule the leap second at the appropriate time via the STP panel, when the leap second occurs, the STP UTC time will be 1 second ahead of the ETS and so steering will occur to correct it. If you do schedule the leap second, then STP generates a "Time Control Parameter Change event" external interrupt that gets processed by z/OS to make the leap second adjustment. If it is a positive change, z/OS spins on all CPUs for the amount of the positive leap second change to ensure there are no duplicate UTC time stamps and updates CVTLSO. No steering is required as STP UTC time remained accurate with the ETS. George Kozakos z/OS Software Service, Level 2 Supervisor ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
