# Presentation: 322942

## CMS DAQ Principles

**   ****Computing Services**

**Level 1**
**Trigger**

**    ****Collisions: ****40 MHz**

**Signals in readout electronics**

**Interesting patterns are forwarded: ****100 kHz**

**~500**** output buffers contain interesting event fragments**

**Event builder network**

**~500**** event filter units inspect complete events**

**Interesting events are forwarded: ****100 Hz ********* 1 MB**

** ****1/11**

**CMS DAQ Principles**

## CMS has only 2 Trigger Levels

- Front end

- Readout

- Network

- Detectors

**L1**

**HLT**

**L1**

**L2**

**L3**

- Front end

- Readout

- Farm

- Network

- Detectors

**CMS has only 2 Trigger Levels**

**“****Traditional”**

**CMS**

**3 levels**

**Level1: ****HW / ASIC / FPGA**

**Higher Level Triggers: ****SW**

- buffers

- buffers

- buffers

- buffers

- Farm

- Tape

- Tape

** ****2/11**

## CMS DAQ Concepts

**How to implement the ****Event Builder****?**

**CMS DAQ Concepts**

** ****3/11**

## CMS EVB – original design

**EVM**

**GTP**

**FED**

**FED**

**FED**

**RU**

**RU**

**RU**

**BU**

**BU**

**BU**

**~500 ****Front End Drivers**

**~500 ****Readout**

**~500 ****Builder**

**100 kHz**

**Global Trigger Processor**

**Event Manager**

**Tough requirements ******** need ****simulation**** of full system**

**Units**

**Units**

**CMS EVB – original design**

** ****4/11**

## Idea:
Simulate 1x1, 2x2, ... 64x64 DAQ test systems
Up to 1/8 of the real system

Compare the results with test measurements
Fix and tune the simulation where needed

Predict the behavior of the real DAQ system
From 64x64 to 512x512 is a big extrapolation...

**Simulate 1x1, 2x2, ... 64x64 DAQ **_**test**_** systems**
- Up to 1/8 of the real system
**Compare the results with test measurements**
- Fix and tune the simulation where needed
**Predict the behavior of the real DAQ system**
- From 64x64 to 512x512 is a big extrapolation...

**The problem with the original EVB design:**

**it cannot be built in ****stages**** ******** is there a better way?**

**CMS EVB Simulation**

** ****5/11**

## CMS EVB – new design

**Up to 8**** slices, routing by event number / DAQ partition**

**CMS EVB – new design**

** ****6/11**

## Advantages of new design

**Can build the full system in stages**
**More slices ******** can take higher rates**
- Low starting luminosity  need fewer than 8
**Slices largely independent**
**Only need to simulate 1 slice of 64x64**
**Largest test setup equals 1 slice**
**Do not have to extrapolate simulation results**
- Simulation now for scanning parameter space

** ****7/11**

## What does the EVM do?

**EVM has 2 logical components:**
**RM = Readout Manager**
- Receives triggers from GTP
- Maps each trigger to a free Event ID
- Informs all Readout Units of the mapping
**BM = Builder Manager**
- Receives event requests from Builder Units
**Each BU may have its own profile for requests**
- Dispenses prepared Event IDs accordingly

** ****8/11**

## Efficient Switch: Barrel Shifting

**Chop**** ****output into chunks of ****fixed size**** (4 kB)**
**Loop over all destinations; send “****filler****” data when needed**

**Efficient Switch: ****Barrel Shifting**

** ****9/11**

## FED, GTP
Custom-designed
Hardware, ASIC, FPGA
RU, BU, EVM, Filter Farm
Standard PC
Custom-designed cards avoided where possible
Typical number of Farm Nodes: 2000
EVB networks / switches
MyrinetTM
250 MB/s, elegant design (“wormhole routing”)
Gbit Ethernet
Very popular  cheap

**Custom-designed**
- Hardware, ASIC, FPGA
**RU, BU, EVM, Filter Farm**
**Standard PC**
- Custom-designed cards avoided where possible
**Typical number of Farm Nodes: 2000**
**EVB networks / switches**
**MyrinetTM**
- 250 MB/s, elegant design (“wormhole routing”)
**Gbit Ethernet**
- Very popular  cheap

**Component implementation**

**10/11**

## Principle of the HLT Farm

**   ****Many small fish...**

**11/11**