FTK variable resolution pattern
banks
TDAQ Week at SLAC – 11/18/2010
G. Volpi – INFN Frascati, MC Fellowship
Associative memory and SS size
Large SS
Small SS
SS size optimization is an hard task, with many variables
Using “large” SS the final AM bank is fully efficient with a
limited number of patterns
Using “small” SS, half the “large” SS, the number of patterns
increase
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Decrease the chance a pattern fires for random hits (noise, tracks
fragments, …)
More patterns, more chips, more €€€ or $$$
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2
Current estimate for the number of patterns per region is 25M for
2013, 5M for 2013-2014, up100M for 2018, 386 M after 2020
G.Volpi - FTK Variable resolution banks
TDAQ@SLAC - 11/18/2010
SS size vs efficiency and road traffic
Pattern size r-f: 24 pixel, 20 SCT 36 pix z
(1.2 mm) (1.6 mm)
(14 mm)
Pattern size r-f: 12 pixel, 10 SCT 36 pix z
(0.6 mm) (0.8 mm)
(14 mm)
90%
65M
500M
# of patterns in Amchips (barrel only, 45 f degress)
The output is very different in a real scenario: i.e. using WHbb@3E34:
<# roads/event @ 3E34> = 342k
3
<# roads/event @ 3E34> = 40k
G.Volpi - FTK Variable resolution banks
TDAQ@SLAC - 11/18/2010
TSP and variable resolution
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Patterns with “large” and “small”
SS could be related:
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One pattern with large SS contains
many patterns with small SS
A tree organization is natural
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AM level
AM is used to search the 1st step
TSP processor could search within
the sub-patterns
TSP banks can be implemented
using less expensive devices
TSP level
Final efficiency depends on the
TSP patterns
4
G.Volpi - FTK Variable resolution banks
TDAQ@SLAC - 11/18/2010
AM performance and TSP relation

Most simple bank with AM
patterns doubling the phi size
of TSP pattern: 1 bit/layer
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Typical reduction factor 3
Most of the AM patterns have
few sub-patterns (1, 2 or 3)
Difference made by
fake AM roads, rejected
at TSP stage
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5
WH@3E34 shows a very small
fraction of AM patterns are
confirmed at TSP level
A strategy able to reject the AM
road with few kids early will
have a large effect
G.Volpi - FTK Variable resolution banks
TDAQ@SLAC - 11/18/2010
Variable resolution AM
We can use don’t care on the
least significant bit when we want
to match the pattern layer @
AM resolution or use all the
bits to match it @ TSP
resolution
TSP patterns
AM
pattern
DC
6
G.Volpi - FTK Variable resolution banks
• All patterns with 1 kid
are stored at TSP
precision
• All the layer without
DC can ignore the hits
in the “wrong” side of
the layer
TDAQ@SLAC - 11/18/2010
DC bits and sub-patterns distributions
Single “kid” AM patterns
Using DC single kid AM patterns are described using the best precision
The number of DC bits in a bank peaks to 1 also for AM patterns with >1
sub-pattern
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The distribution shows how the sub-patterns are strongly correlated
The DC bit in the AM chip increases the number of cells used to describe
a pattern: from 15  16
The increase is 1/15~7%, the equivalent TSP bank is 3 times bigger
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7
G.Volpi - FTK Variable resolution banks
TDAQ@SLAC - 11/18/2010
Simulation strategy
The FTK simulation was modified to include the DC bits
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Option A only simulation: 3 pixel layers + 4 SCT axial layers
Option B test is ongoing
3 pileup scenarios were studied: 17, 40 and 75 pileup events
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For each pile-up scenario a different bank is chosen to try to meet
chip development and LHC schedule
The working point for each scenario is decided fixing the TSP
size to have an efficiency >=90% and following our experience
For each scenario the extracted numbers are:
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8
Number of roads/processing units at different simulation level using
barrel only simulation:
Final numbers assuming16 processing units
G.Volpi - FTK Variable resolution banks
TDAQ@SLAC - 11/18/2010
Road flux Bank 96x80x72
10000
8000
TSP Total bank size 5 MP
Median
0
2000
50% of events
95% of events
6000
Bank studied using WHbb
with 17.6 pileup events.
4000
# roads
Road flux 17.6 PE
TSP
AM@TSP
AM@DC
AM
TSP roads
Average number of road at
different levels per
processing unit:
2020384283423
Strong reduction using DC,
about 5.
Most of the DC roads are
confirmed by the TSP (74%)
Often AM roads have more
AM board
than 1 TSP roads
TSP bank 48x40x72
output
AM roads confirmed at
AM roads
TSP level
confirmed by DC
9
G.Volpi - FTK Variable resolution banks
TDAQ@SLAC - 11/18/2010
Road flux Bank 48x40x36
60000
Road flux 40 PE
50000
Bank studied using WHbb
with 40 pileup events.
30000
The number of roads at the
different levels per
processing unit:
20000
14780260015532286
10000
The DC suppression factor
5.6
0
# roads
40000
TSP Total bank size 100 MP
TSP
AM@TSP
AM@DC
AM
TSP bank 24x20x36
10
G.Volpi - FTK Variable resolution banks
TDAQ@SLAC - 11/18/2010
Road flux Bank 24x20x36
Roads flux 75 PE
15000
Bank studied using WHbb
with 75 pileup events.
10000
Number of roads at the
different levels per
processing unit:
5000
21400330017702380
DC reduction factor 6.5
0
# roads
TSP Total bank size 384 MP
TSP
AM@TSP
AM@DC
AM
TSP bank 12x10x36
11
G.Volpi - FTK Variable resolution banks
TDAQ@SLAC - 11/18/2010
Summary tables
Average number of roads/units*
AM
AM w/ DC
AM w/ TSP
TSP
17.6 evts
5040
959
709
1060
40 evts
37000
6500
3880
5720
75 evts
53500
8250
4430
5950
No DC in old
AM chip
To be compared with a limit of 8000 output roads.
The 75 pileup events exceed that limit indeed at that time (2020) a
more powerful chip should be used: 8L and maybe better use of DC
with more bits/layer
* the number are corrected x2.5 to include the traffic in the endcaps. 16 processing
units are assumed
12
G.Volpi - FTK Variable resolution banks
TDAQ@SLAC - 11/18/2010
Conclusions
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The use of DC bits gives the opportunity to strongly
reduce the number of roads
DC does most of the work of the TSP
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Use of variable resolution patterns for option A showed
promising results
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Is the TSP really necessary?
Further optimizations are possible
The number of roads confirmed by he DC is within the
required limit
Variable resolution and DC are generic, test using the
same algorithm in FTK option B ongoing
13
G.Volpi - FTK Variable resolution banks
TDAQ@SLAC - 11/18/2010
Backup slides
14
G.Volpi - FTK Variable resolution banks
TDAQ@SLAC - 11/18/2010
Combination flux Bank 96x80x72
1000000
The flux of the
combinations is also largely
effected the DC.
600000
The average number of
combinations is (x103):
200000
92.311.69.17.2
0
# Combinations
Combination flux
TSP
AM@TSP
AM@DC
AM
TSP bank 48x40x72
15
G.Volpi - FTK Variable resolution banks
TDAQ@SLAC - 11/18/2010
8e+05
6e+05
The average number of
combinations is (x103):
15719.912.89.58
2e+05
The flux of the
combinations is also largely
effected the DC.
4e+05
Combination flux
0e+00
# Combinations
Combination flux Bank 48x40x36
TSP
AM@TSP
AM@DC
AM
TSP bank 24x20x36
16
G.Volpi - FTK Variable resolution banks
TDAQ@SLAC - 11/18/2010
Combination flux Bank 48x40x36
2000000
The average numbers of
combinations are (x103):
1500000
23728.516.312.7
1000000
AM@DC accounts for the
hits in the unused part of
the AM pattern.
500000
AM@ TSP can use only the
standard DC mask.
Could a dynamic DC mask
reduce the fits’ number?e
0
# Combinations
Fit combinations
flux
TSP
AM@TSP
AM@DC
AM
TSP bank 24x20x36
17
G.Volpi - FTK Variable resolution banks
TDAQ@SLAC - 11/18/2010