DT Upgrade: Phase 2 RO

C. F. Bedoya December 11th, 2012 2

TSWG (Trigger Strategy Working Group)

CMS is discussing the possibility of operating in Phase 2 with:

- 1 MHz L1A rate (instead of 100 kHz)- 20 us latency (instead of 6 us as previously assumed. Now 3.2 us)

We are asked to provide statements about the implications in our subsystem.

Two meetings already took place:- https://indico.cern.ch/conferenceDisplay.py?confId=195153- https://indico.cern.ch/conferenceDisplay.py?confId=200590

It appeared unlikely because it meant replace all ECAL electronics, but now this is not considered so difficult.(Would this mean that tracking trigger is not so mandatory if we can increase the trigger rate to 1 Mhz? not clear)


Higher LHC luminosity will imply larger occupancies in the DT chambers, which will turn into a higher hit frequency. The consequences of this higher occupancy are the following:

-increase buffers occupancy at the different levels-slow down the time to process an event (reduce processing speed)-increase the required bandwidth for the output link

Increase of trigger rate and/or trigger latency only makes this scenario even harder.

* L1A rate and latency will impact only readout chain

* ROS will be redesigned between LS1 and LS2.

* Will try to incorporate DDU functionality to remove further bottlenecks

* i.e. impact is on the ROB


Rate outside the trains, no muons included (basically neutrons)

Big difference between chambers,:

- YB-2 S4 MB4 27 kHz/TDC channel- YB-/+2 MB1s 12 kHz/TDC channel

Accounting inside trains may increase 3.6 kHz in MB1 and 0.3 kHz in MB4 (¿?)

From Gianni CMS week June

1035

1035


Gianni CMS week June

* Upper sectors MB4* Leaks between barrel and endcap in MB1s

C. F. Bedoya December 11th, 2012 6From I. Redondo

YB-/+2 MB1s at 1035 : 350 kHz “muon” rate (per chamber)114 kHz “muon” rate per ROB29 kHz “muon” rate per TDC

This are chamber rates (DTTF input counters)

Phi rates


From I. Redondo

eta


Hit rate 27 kHz => 37 us between hits. Since there are:128 channels/ROB, => one hit per ROB each 0.29 us (3.5 hits/ROB/event)32 channels/TDC, => one hit per TDC each 1.2 us.

Including muons, adds 8 hits per L1buffer FIFO (or more):Worst muon rate 350 kHz => 29kHz/TDC => 1 muon every 35 us/TDCHits stored in L1buffer until the L1A arrives.

So if the L1A latency was 20 us, this means we will have to store max 1 hit/channel, i.e. 32 hits/TDC until the L1A arrive + 8 hits/TDC from muons until the L1A arrive This represents 12 hits per L1buffer FIFO/event, while they are 256 positions in the FIFO.

It seems it should be possible to work with 20 us latency in phase 2


-Readout FIFO-Event processing speed-Output link bandwidth

Time window is approximately 1 us, and we will have 1 hit/TDC each 1.2 us, that is the number of hits per event that are expected to be stored in the Readout FIFO

But the limiting factor is the speed at which you output the data

byte-wise mode at 20 MHz Header,trailer, hits = 32 bit words

It takes 8 BXs to send each hit (minimum) + 16 BXs header+ trailer+ 8 BXs token sharing + seems there is more... (next slide)


No muons

<- 3.5 hits/ROB

Max 500 kHz... probably optimisticIf one includes the worst case muon rate (350 kHz/chamber => 1 muon/ROB every 9 us) => MAX 300 kHz

(one could reduce the time window, increase the threshold or start being inefficient...)

Test perform on a ROB at lab with fixed trigger rate:


• trigger matching: reduces the payload. (100 kHz L1A rate => one L1A each 10 us with a sampling window of 1 us => we read 10% of the time)

• At 1 MHz L1A rate => we will be reading 100% of the data, thus trigger matching is an overhead

of processing time and bandwidth (headers and trailers)

• In principle, it is possible to run the HPTDCs in continuous mode:• - hits sent as arrive from chambers, • - time measurement referred to BC0

• Latency and L1A rate becomes irrelevant for the ROB

• Trigger matching in the new ROS may be possible (needs study and will imply detailed calibration of the different absolute BXs ID between the ROBs and the ROS).

• It may open possibility to use TDC data in the trigger (?)... (output delay not deterministic and long...)

• Limiting factor in this mode of operation is the bandwidth of the readout link:

27 kHz * 128 ch * 32 bits/hit = 110 Mbps

• With muons (350 kHz/chamber => 114 kHz/ROB of 8 hits muons => 114 Mbps

• Max bandwidth is 160 Mbps => hit rate 39 Hz/cm2 (to be checked) MB4s are close...

• This may work depending on the uncertainty of the background. If it is large, then we start o be inefficient


• We don´t expect any problem for running present ROBs design with Phase 2 occupancies and 100 kHz L1A rate and 6 us L1A latency

• With the background rates expected in Phase 2, it is unlikely that we could run at a trigger rate higher than 500 kHz.

• Latencies of 20 us could likely be achieved, although proper testing should

be done. • HPTDCs could be operated in continuous mode, which should allow

operation with 20 us latency and 1 MHz trigger rate. However, this means no background reduction is possible playing with the time window (no filtering is done, all hits are sent). Therefore, we could start to loose efficiency for background rates larger than 39 Hz/cm2. (This number should also be checked). MB4 rates are too close to this number (27 Hz/cm2 for YB-2 S4 MB4).

• Any action to place a shielding in the MB4s of the upper sectors or in the

MB1s of the external wheels will reduce any possible efficiency drop. • Considering the large uncertainties (energy, extrapolation, target

luminosity, etc), even if the MB4s can be shielded, replacing the ROBs of the MB1s external wheels with a higher performance board, should also not be discarded

• In order to operate in continuous mode, a DC balancing is mandatory at

CUOF level.

DT Upgrade: Phase 2 RO

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