1. Serial link Loss-of-Lock impact on trigger distribution dead time
24/01/2018
Serial link Loss-of-Lock impact on trigger distribution dead time
Sergio Cavaliere
Department of Physics, University of Napoli “Federico II”, Italy
and
INFN Sezione di Napoli, Italy
In this talk I will present some results from a preliminary study of Forward Correcting Codes for the SuperB serial links, simulations results and tools built for the purpose.
It’s actually an ongoing work which will require soon a closer integration to the architecture which are being studied for the actual link.
XIV SuperB Workshop – LNF Frascati - Sept, 2010

2. XIV SuperB Workshop – LNF Frascati - Sept, 2010
Introduction
Recall the error sources due to SERDES Serializer-Deserializer in a radiation hard environment
Describe the problem under analysis, that of Loss Of Lock due to bit failures in specific bit positions
Describe some features of the Poisson statistics of this source of errors or better missed data
Describe the parameters analyzed in order to evaluate the impact of LOL events
Describe the simulation performed and the histogram and charts useful in order to evaluate the impact of LOL events on the performance of the overall architecture
Conclusion and future work
XIV SuperB Workshop – LNF Frascati - Sept, 2010

3. SerDes in rad enviroments
Rad hard
Fixed latency
under test
Connections:
From the FCTS to the detector
From the detector to the subdetectors
Layout by D. Breton
LNF, Dec.09
FCTS link
Tight latency requirements
DS92lv18
SuperB Workshop - SLAC, Oct.09

4. Which bits may be protected against errors? not of concern today
start
stop
only these bits may be protected bit
20bit symbol: start, 18bit payload, stop
Guaranteed transitions at the symbol boundary
No encoding provided, pattern is transmitted as-it-is
61.2 MHz x 20 -> 1.2 Gbit/s, 1.1 Gbit/s user bandwidth, 1 UI = 817 ps
SuperB Workshop - SLAC, Oct.09

5. Loss-of-lock: no recovery is possible
Error injection
Error flag
RX recovered clock
LOCK*
Loss-of-Lock
Lock achieved
Each and every missing start/stop triggers a loss-of-lock
Then, the RX automatically tries to lock on the stream
Lock is (should be) guaranteed by SYNC patterns: BELLE reports a few problems with older components, no issues have been seen during our tests
SuperB Workshop - SLAC, Oct.09

6. Loss-of-lock recovery sequence
Transmission restarts
ECS signals lock to the TX via Ethernet TX RX
ECS
ETHERNET
LOL signalled to TX
and later
Resynch happened
Synchronization command
Red: Loss Of Lock handling
Black: normal operation
commands
RX reveals LOL event
ECS acknowledges LOL and signals it to the TX via Ethernet which in turn issues a re-synch command
RX starts relocking T2
T1a
T1b T3
XIV SuperB Workshop – LNF Frascati - Sept, 2010

7. XIV SuperB Workshop – LNF Frascati - Sept, 2010
24/01/2018
Involved times
T1 it is the time needed to traverse the message trough Ethernet. It
depends on the performance of the Ethernet, the communication procedure, etc.
We will take into consideration the following figures
T1 = 5ms 20ms 50ms 75ms 100ms +/-10%
T2 is the the time needed to the receiver to inform the ECS that lock was lost
0.1 ms -0.5 ms -1.0 ms
T3 is the recovery time in the RX .
Uniform distribution between 500ns e 1000ns
XIV SuperB Workshop – LNF Frascati - Sept, 2010 7

8. Loss Of Lock: statistics of the recovery duration
24/01/2018
Loss Of Lock: statistics of the recovery duration
T1 = 5ms 20ms 50ms 75ms 100ms +/-10% Ethernet +ECS
T2 time to signal lock lost to the ECS 0.1 ms -0.5 ms -1.0 ms
T3 lock time in RX. Uniform pdf 500ns e 1000ns
The three times add up to a pdf resulting from the convolution of the three pdfs
Since T3 has uniform pdf 500ns to 1000ns it may be neglected
Overall pdf is essentially determined by the sum of T1 and T2, both normal.
It will be normal showing parameters
σ1232=σ12+σ22 e µ123= µ1 + µ2
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9. Loss Of Lock: pdf of the recovery duration
24/01/2018
Loss Of Lock: pdf of the recovery duration
(s)
T1 = 5ms 20ms 50ms 75ms 100ms +/-10%
T2 = 0.1 ms -0.5 ms -1.0 ms
T3 = 500ns ns
XIV SuperB Workshop – LNF Frascati - Sept, 2010 9

10. Loss Of Lock events: Poisson statistics
24/01/2018
Loss Of Lock events: Poisson statistics
Loss of Lock has the usual statistics giving
the number of events which take place in a radiation hard environment
one after the other and indipendently each other
the average number of events in unit time is constant, equal to λ.
λ is the average number of events in unit time (frequency or rate)
μ =1/ λ is the average time distance from one event to the next
λ is the average number of events in unit time (frequency or rate)
μ =1/ λ is the average time distance from one event to the next
XIV SuperB Workshop – LNF Frascati - Sept, 2010 10

11. Loss Of Lock events: diffferences from thePoisson statistics
24/01/2018
Loss Of Lock events: diffferences from thePoisson statistics
After a Loss Of Lock events takes place a recovery procedure is needed before the link is active again and a new LOL may happen.
Time distance between one event and the next cannot be less than recovery time.
The statistics is slightly modified in the origin of the times
but
Recovery time max is 100ms
Average time distance ranges from 1 hour 10 days
The statistics is practically unaffected
XIV SuperB Workshop – LNF Frascati - Sept, 2010 11

12. XIV SuperB Workshop – LNF Frascati - Sept, 2010
24/01/2018
Loss Of Lock impact on average for each single link Foreseen range [1h 2h 4h 12h 1day 5days 10days]
From the test beam we know the
average no of LOL events for a link
Because of n LOL events in unit time
a link will be off for n*LOL_duration
seconds
We may define the ratio: 75 50 20 10
5 ms
1 LOL event each 1/ day
10ms LOL recovery duration
toff/ton = 4E-4%
Average time distance for LOL events
(s)
BUT
What happens when we have links working at the same time in response to a flow of triggers in the kHz range?
This requires thorough simulations.
XIV SuperB Workshop – LNF Frascati - Sept, 2010 12

13. The problem to be faced 1/2
24/01/2018
The problem to be faced 1/2
Here is a sketch in the case of 3 links only
rad events and LOL recovery intervals
rad events and LOL recovery intervals
rad events and LOL recovery intervals
link 1
link 2
green: LOL events affecting 2 links
Blue: LOL events affecting 3 links
link 3
XIV SuperB Workshop – LNF Frascati - Sept, 2010 13

14. The problem to be faced 2/2
24/01/2018
The problem to be faced 2/2
LOL event
100kHz Trigger stream
LOL recovery interval
If a channel has its links impaired in some time instant it will not deliver the command to acquire data for that trigger
If many links are likely to be impaired at the same time, data quality will be strongly affected because data from many channels will be missing
We would like to know:
How many triggers are canceled for too many links thus causing significant loss of information for those triggers?
What is the statististics of the number of links impaired (because of a LOL event) for the same trigger?
These question may be answered by means of long simulations, as follows
XIV SuperB Workshop – LNF Frascati - Sept, 2010 14

15. A single situation (intermediate case)
24/01/2018
A single situation (intermediate case)
LOL recover time 20ms
Trigger frequency =150 kHz
Average time interval between two consecutive LOL events 1day
Simulation: 1 year of the apparatus
Each trigger is sent through 1000 links to 1000 channels
So it is important to undertstand the statistics of LOL in the different links
As a result of simulations in this case the percentage of triggers with
1 link impaired and then data missing from 1 channel is 0.02% of the overall triggers
2 links impaired and then data missing from 2 channels is 2.7E-6%
3 links impaired and then data missing from 3 channels is 6E-8%
4 links impaired and then data missing from 3 channels is 2E-8%
5 links impaired and then data missing from 5 channels is 0.0%
Likely: No more than 4 links for the same trigger are unable to transmit the trigger command.
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16. Histogram for the intermediate case on a log scale
24/01/2018
Histogram for the intermediate case on a log scale
LOL recover time 20ms
Trigger frequency =150 kHz
Average time interval between two consecutive LOL events 1day
Simulated time of the apparatus 1year
Trigger with impaired links
1 link 0.02%
2 links 3E-6%
3 links 6E-8%
4 links 2E-8%
5 links 0%
Trigger frequency =150 kHz
6E-8%
2.7E-6%
2.0E-8%
0.023%
0.0%
LOG SCALE
No. of links impaired
0.0%
XIV SuperB Workshop – LNF Frascati - Sept, 2010 16

17. XIV SuperB Workshop – LNF Frascati - Sept, 2010
24/01/2018
Intermediate case: LOL recovery lasts 20ms LOL interval 1h 2h 4h 12h 1day 5days 10days
0.55%
0.001%
3E-6%
5E-7
0.55
0.02%
6E-8%
2E-8%
XIV SuperB Workshop – LNF Frascati - Sept, 2010 17

18. XIV SuperB Workshop – LNF Frascati - Sept, 2010
24/01/2018
Intermediate case: this equivalent chart allows easily reading histogram values
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19. Worst case : longest LOL recovery time and shortest LOL interval
24/01/2018
Worst case : longest LOL recovery time and shortest LOL interval
LOL recover time 100ms
Trigger frequency =150 kHz
Average time interval between two consecutive LOL events 1hour
Simulated time of the apparatus: 1year
2.7%
Trigger with impaired links
1 link 2.7%
2 links 0.04%
3 links 4E-4%
4 links 4E-6%
5 links 0%
0.04%
4E-4%
4°-6%
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20. Worst case: LOL recovery lasts 100ms
24/01/2018
Worst case: LOL recovery lasts 100ms
LOL average time distances:
1h 2h 4h 12h 1day 5days 10days 0%
0.009%
4E-5%
1e-6%
1.4%
6e-7%
03e-8%
9e-9
0.01%
6e-5%
3e-7%
9e-8%
0.1%
0.04%
4E-4%
4E-6%
2.7%
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21. XIV SuperB Workshop – LNF Frascati - Sept, 2010
24/01/2018
Worst case: this equivalent chart allows easily reading histogram values
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22. Best cases: LOL ricovery time is 5ms
24/01/2018
Best cases: LOL ricovery time is 5ms
Data from the green histogram:
Average rad interval 12 hours simulated for 1year
Trigger with missing links
1 link 0.012% triggers
2 links 8E-7%
in 3 links 3E-8%
in 4 links 9°-9%
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23. Best case: LOL ricovery time is 5ms
24/01/2018
Best case: LOL ricovery time is 5ms
LOL recover time 5ms
Average rad interval 1day simulated for 1year
Trigger with missing links
1 link % triggers
2 link 1.161e-007%
in 3 link 1.513e-008
in 4 link 4.679e-009%
Trigger frequency =150 kHz
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24. Conclusion and perspectives
24/01/2018
Conclusion and perspectives
Statistical analysis of the impact of Loss Of Lock on data quality has been set up
Many alternatives has been analyzed in order to understand the impact of the problem on design parameters
To be done:
Understand the impact on fata quality and front end synchronization
More thorough error analysis is on the way and some results have been obtained
Impact on the error performance of the choice between uncoded, Hamming coded or ReedSolomon coded data transmission in terms of coded error probability.
XIV SuperB Workshop – LNF Frascati - Sept, 2010