Minutes of the 8^th Timing Working Group Meeting (TimWG)
Held on Friday the 20^th August 1999

  Present:

Excused:

            Philippe BAUDRENGHIEN, Julian LEWIS, John PETT.

Agenda

• Approval of previous minute
• Review of the different timing requirements and locations.
• LHC timing events based on absolute time
• Next speakers & next meeting

Approval of previous minutes

There wer no corrections on the previous minutes.

Review of the different timing requirements and locations

Gary BEETHAM presented a first summary of the different timing requirements:

• LHC bunch frequency,
• LHC revolution frequency,
• LHC 400 Mhz RF frequency,
• LHC slow timing,
• LHC injection prepulse.

For reference, Gary BEETHAM provided a list of timing specialists concerned by the different requirements.

LHC timing events based on absolute time

Quentin KING presented a proposition for the distribution of LHC timing events based on absolute time (see slide attached).

This solution proposes to remove the TG8 cards from the middle level gateway, to replace them with the distribution of timing events through the communication network with an absolute time reference and to implement a deterministic event distribution mechanism based on an acknowledge procedure between the low and the top levels. This approach permits to extend the deterministic characteristics of the low level WorldFIP fieldbus timing distribution to the complete timing event distribution.

During the following discussion, different technical points were raised:

• Thomas BOHL proposed that a comparison table between the actual and the proposed solution should be made,
• Michel JONKER explained that the MTG has to know who is listening to a specific event and that the handshaking procedure between MTG and clients can become extremely difficult and complicate to maintain and have an impact on the reliability of the complete system. He raised up also the questions of  the communication network reliability, stability and availability and the possibility to transmit deterministic events with  TCP protocol.
• Question KING explained that a continuous background polling by the MTG. is foreseen in order to check that the clients are alive and synchronized and that the network to the client is working properly. He reminded also that this approach reduce significantly the cabling cost and the complexity of the timing distribution for the power converters. He outlined, once more, that for a good LHC operation, the correct synchronization of all the power converters is mandatory.

It appeared clearly that this proposition can be useful for timing event distribution to different types of equipment. In general, the electronics will become significantly simpler, adaptable to specific user requirements and cabling cost and complexity will be reduced. On the other hand, software complexity at the MTG level will be increased and reliability has still to be evaluated. In conclusion, this proposition has to be studied more in detail and the impact of the different possible technical choices has to be evaluated.

Next meeting

Next Meeting will be held on Friday 27 August 1999 at 10:00 AM in 864 1C01.

Agenda

1. Approval of previous minutes
2. Timing requirements for machine operation. Michel JONKER & Mike LAMONT
3. Computer synchronization. Pal ANDERSSEN
3. Next speakers & next meeting
4. AOB