Timing for AP: introduction Javier Serrano AB-CO-HT 15 September 2006

Plan for the morning  Intro, context, hardware. Javier.  General timing concepts. Julian.  Central Timing. Jean Claude.  Distributed Timing. Ioan.  Visit of central timing and BA3 Faraday Cage.  Hands-on demo.

The timing team  One of the 3 broad activities of the HT section.  Three SW FTE:  Julian: activity leader, low level software.  Jean Claude: central timing, libraries.  Ioan: distributed timing.  Broad mandate: sync services for all accelerators at CERN, both HW and SW.  Strong ties to operation, many installed systems -> very visible activity.  Big inter-dependencies with all layers of control system -> need to communicate a lot.  Many clients with different (sometimes conflicting) requests -> continuous evolution, sometimes causing unavoidable instability.  Overall though, very successful system. Injectors can change function completely every 1.2 seconds!

GPS One pulse per Second GPS Smart clock PLL One pulse per Second Phase locked 10MHz Basic Period 1200/900/600 ms Advanced (100us) One pulse per Second Synchronized 1KHz (slow timing clock) Phase locked 10MHz Phase looked 40 MHz Event encoding clock 40MHz PLL CTSYNC RS485 Timing CTGU The new generation low jitter <1ns VME based MTG module UTC time (NTP or GPS) Event tables External events General Machine Timing (GMT) Hardware Architecture CERN UTC Time Set once on startup & on Leap Seconds RS485 Timing CTRP 40 MHz 10 MHz 1 KHz 1PPS Delay Control System CERN UTC Time 25ns steps Timing receiver

UTC: the basis for GMT at CERN  Very precise atomic time standard.  Uniform seconds defined by International Atomic Time.  Leap seconds added every ~18 months to compensate for the Earth’s slowing rotation.  Warning 1: Subtraction of two dates must in principle consult a table of leap seconds.  Warning 2: other time scales (like UNIX time, GPS time and TAI) do not use leap seconds.  UTC is nevertheless the most used system because all legal time is referenced to it.  All leap seconds happen at midnight on June 30 or December 31.

GMT cards  CTG: Controls Timing Generator. Runs “event programs” in a dedicated CPU. Its output drives one GMT network.  CTR: Controls Timing Receivers. They produce pulses and interrupts in response to GMT events.  CTRV: VME format.  CTRP: PMC format.  CTRI: PCI format.