Reports and Measurements

This page serves to collect reports and measurements on the GMT.

Timing Receivers

Network

The Unofficial Feature List

Although the subject is extremely complex, it is tried to summarize the status of some key characteristics of the GMT in the following table. It is intended to give safe (worst case) values of the actual performance including a reference; same for the specification. Values are taken at various conditions that might not be representative.

Sub-SystemSorted ascending Item Stat Reported Value Specified Value Date Rep (Spec) Ref Rep (Spec) Remark
Data Master @2018              
Data Master @2018 upper bound latency per lm32 CPU DONE < 500 us @ 16 msg (sl) 500 us [2] (sl) 12/2017 (12/2017) minutes (./.) update 2018-sep-03: max reported upper latency is 505 us
Data Master @2018 throughput per lm32 CPU DONE > 16 messages @ 500 us 16 msg. @ 500 us 12/2017 (12/2017) minutes (./.)  
Data Master @2018 capacity per lm32 CPU processing 600 msg @ 2018 600 msg @ 2018 12/2017 (12/2017) minutes (./.) 1 control block 'eats' 11msg
Data Master @2018 number of patterns lm32 CPU processing 4 @ 2018 > 10 ? 12/2017 (12/2017) minutes (N/A) not really specified; 4 patterns ok for 2018
Data Master @2018 number of lm32 CPU ALERT! 3 8 ? 12/2017 (2012 ?) minutes (N/A) not really specified; 3 cores ok for 2018
OS              
OS CentOS RT: task switching latency DONE 100 us (ub), 20 us (av) < 1 ms (?) 09/2018 (<2010 ?) priv comm. from HEL (SR) measurement on SCU using preempt-test, only 3us gain without hyperthr
Timing Network              
Timing Network upper bound latency DONE < 390 us @ 4 WRS layers 500 us [1] 06/2016 (2012 ?) report (minutes, wiki) F-DS-C-05e mentions '200 us' as 'should'
Timing Network throughput (messages) DONE > 16 messages @ 500 us (sl) 16 msg. @ 500 us (sl) 12/2017 (12/2017) Dry Run #3 ( minutes )  
Timing Network throughput (frame size) ALERT! < 60 MBit/s 100 MBits/s 08/2016 (09/2014) report (wiki) 1 to N ports @ 64 bytes/frame, ok for 2018
Timing Network loss rate ALERT! < 2e-8 @ 600 Hz msg. rate 1e-12 08/2016 (01/2013) wiki (F-DS-C-05e) without forward error correction, ok for 2018
Timing Network loss rate ALERT! > 90% @ > 10% bandwidth 1e-12 08/2016 (01/2013) wiki (F-DS-C-05e) for small packets of 64 and 128 bytes. Better for larger packets.
Timing Network max numbers of WRS layers DONE 4 5 06/2016 (2012 ?) report (various minutes) maybe 4 layers are sufficient
Timing Receiver              
Timing Receiver FTRN userland latency @ API DONE 93 us (ub), 62 us (av) < 1 ms (?) 12/2012 (<2010 ?) article (N/A) 1 ms spec is overal FEC performance
Timing Receiver FTRN userland latency @ saftlib ALERT! 2500 us (ub), 1400 us (av) < 1 ms (?) 11/2017 (<2010 ?) wiki (N/A) 1 ms spec is overal FEC performance, ok for 2018
Timing Receiver FTRN output (Lemo) jitter (RMS) DONE 20 ps (av) 100 ps 11/2014 (01/2013) article (F-DS-C-06e) 'term jitter' defined in F-DS-C-05e
Timing Receiver FTRN output (Lemo) precision (RMS) DONE 50 ps (av) 1 ns 11/2014 (01/2013) article (F-DS-C-06e) 'term precision' defined in F-DS-C-05e
Timing Receiver FTRN output (Lemo) accuracy (RMS) DONE ok, needs re-checking with every release 2-3 ns 11/2014 (01/2013) wiki (F-DS-C-06e) 'term accuracy' defined in F-DS-C-05e
Table: Status of key characteristics of the GMT. Some values are marked by upper bound (ub), or average (av) or sliding window (sl).

[1] The Data Master sends messages to the White Rabbit network 500 us ahead of their scheduled time. The budget of 500 us includes the processing time in the timing receiver.
[2] The upper bound latencies of the network and the data master must be added. It was decided to use a total upper bound latency of 1 ms for the 2018 beam time. Update: The '1ms upper bound' is kept for the 2019 und 2020 beam times.

-- DietrichBeck 2019 October 10
Topic revision: r27 - 18 Feb 2021, DietrichBeck
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