GBT, an integrated solution for data transmission and TTC distribution in the SLHC
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GBT, an integrated solution for data transmission and TTC distribution in the SLHC Perugia, 17 May 2006 A. Marchioro, P. Moreira, G. Papotti CERN PH-MIC. Outline. GBT an upgrade for: Data, TTC and Slow Control links GBT operation: Operation and Data modes Some link topologies

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Outline

GBT, an integrated solution for data transmission and TTC distribution in the SLHCPerugia, 17 May 2006A. Marchioro, P. Moreira, G. PapottiCERN PH-MIC


Outline

Outline

  • GBT an upgrade for:

    • Data, TTC and Slow Control links

  • GBT operation:

    • Operation and Data modes

  • Some link topologies

  • Line codes and error correction

  • System bandwidth

  • New functionality

  • Practical developments

  • Summary

GBT


G igabit b idirectional t rigger and data link

Gigabit Bidirectional Trigger and Data Link

  • The target is to build a system based on a single ASIC which can provide a complete (link) solution for:

    • Timing

    • Trigger

    • Slow Control

    • Data Transmission

  • It will be the SLHC replacement of:

    • TTCrx + GOL + CCU (or equivalent device)

  • For data transmission links:

    • Increase the bandwidth

    • Add redundancy to coupe with higher SEU rates

  • For triggers links:

    • New CMOS technologies open a whole range of possibilities as is discussed next

GBT


Ttc link upgrade rationale

TTC Link Upgrade Rationale

  • Must be ready for SLHC higher demands

  • Must be built on the past experience:

    • Merits

    • Weak points

  • Profit from today's submicron technologies:

    • Higher performance:

      • Larger bandwidth

      • Complex commands can be sent and executed in a single bunch crossing interval

    • Higher integration:

      • Increased functionality

      • Bi-direction link

      • Robust error correction

      • Robust handling of SEUs

  • Profit from today’s optoelectronics technologies:

    • Bi-directional optical network

GBT


Current ttc system limitations

Current TTC System Limitations

  • Transmission of a single trigger type

  • Unidirectional system, return requires additional network

    • Not adapted to build a complete slow-control network

  • Channel-B commands are:

    • Relatively slow

    • Individually addressed commands “non-deterministic”.

  • No error correction on trigger bits (channel-A)

  • Unspecified clock frequency if input link not present

  • Clock quality not sufficient for GHz links

GBT


The new gbt transceiver

The new GBT Transceiver

  • GBT transceiver operation:

    • Operation modes:

      • Trigger:

        • TTC functions

      • Link

        • General purpose

        • Simplex/Duplex

    • Data transmission modes:

      • Continuous

        • Data is continuously transmitted

      • Packet

        • Data is transmitted in burstsof packets

Link

RX

TX

GBT

User Application Side

(Electrical world)

GBT


Gbt operation modes

GBT Operation Modes

  • Continuous mode (think about a traditional optical link):

    • Each link is 100 % occupied by a single transmitter.

    • The transmitter/receiver pair is fully synchronous at all times

    • This is the case for:

      • A trigger source sending data to several trigger destinations

      • Synchronous point-to-point data link

  • Packet mode (think about a backplane bus):

    • Common Transmission medium is shared:

      • A transmitter can only send data upon the request of a master transmitter

    • Several devices can share the same medium and thus communicate with the same destination without collisions

    • This is the case for:

      • Trigger return link (bus)

      • Asynchronous point-to-point data link

GBT


Gbt system configuration 1 broadcast network

GBT System Configuration 1: Broadcast Network

  • Down-path: Passive Optical Tree

    • Current TTC system architecture

    • One source to N destinations

    • For large N, an high optical power source is required

    • Operation mode: continuous

GBT


Gbt system configuration 2 broadcast network with o e o repeaters

GBT System Configuration 2: Broadcast Network with O/E/O Repeaters

  • Down-path: Passive/Active Tree

    • Passive power splitting with electrical regeneration

    • One source to N destinations

    • Optical or electrical: 1-to-8

      • Moderate optical power at each transmitter

    • Operation mode: continuous

    • Moderate increase in latency: o/e-r-e/o

GBT


Gbt system configuration 3 point to point

GBT System Configuration 3: Point-to-Point

  • Up/Down-paths: Optical

    • Full bandwidth available for data transmission

    • Simplex/Duplex operation

    • Operation mode: continuous

GBT


Gbt system configuration 4 bidirectional one to n n to one

GBT System Configuration 4: Bidirectional One-to-N / N-to-One

  • Down/up-links: Passive Optical Trees

    • Passive optical tree in both directions

    • Down-link: 1 source to N destinations

    • Fan-In-Out: 1-to-8 or perhaps 1-to-16

      • For moderate power optical source

      • Possibility of WDM to reduce the optical source power

    • Operation mode:

      • Down-link: continuous

      • Up-link: packet

      • Up-link under control of the master transmitter

GBT


Line codes and error correction

Line Codes and Error Correction

  • To deal with higher SEU rates in SLHC the following scheme is proposed:

    • 64-bit data is first scrambled for DC balance

    • The scrambled data is Reed-Solomon encoded: 16-Bit CRC field

    • An 8-bit redundant header is added to form a frame

    • This results in an 88-bit frame.

      • Line rate  40 MHz × 88-bit = 3.52 Mbit/s

    • To minimize the dead-time due to a loss of synchronization the scrambler is designed as self synchronizing:

      • One LHC clock cycle is enough to synchronize the scrambler

    • The efficiency of the line encoding is: 64/88 = 72.7 %

GBT


Data rate and user bandwidth

Data Rate and User Bandwidth

  • Transmission data rates must be multiples of the (S)LHC bunch crossing frequency:

    • Trigger system remains synchronous with the accelerator cycles

    • Fixed latency communication channels

    • 130 nm CMOS technology:

      • Raw 3.2 Gbit/s ok, (~5 Gbit/s maybe feasible)

      • Transmission of 88-bits encoded at 40 MHz (the LHC rate)

      • Effective data bandwidth of 2.56 Gbit/s (for 3.2 Gbit/s raw)

    • 90 nm CMOS technology:

      • Raw 6.4 Gbit/s ok, (~10 Gbit/s maybe feasible)

      • Transmission of 128-bits properly encoded at 40 MHz (the LHC rate)

      • … or transmission of 64-bits encoded at 80 MHz (the SLHC+ rate)

      • Effective data bandwidth of 5.12 Gbit/s (for 6.4 Gbit/s raw)

GBT


The gbt as a ttc controller transceiver

The GBT as a TTC/Controller transceiver

data

GBT

trigger

1-Wire

I2C Master (3 – wires) (×4)

JTAG Master (4 – wires) (×1)

SPI Master (3 + 5 – wires) (×1)

Parallel port (4 × 8-bit) (×1)

Memory bus (A 16-bit, D 16-bit)

Phase programmable clocks (×4)

Trigger emulator (4 – wires) (× 1)

Event Counter

Bunch Counter

Receiver control

Link Flow control

Transmitter control

I2C Slave

JTAG Port

Receiver

Transmitter

data

GBT


Gbt block diagram

GBT Block Diagram

Lim

Amp

CDR

& PLL

Ser/Par

Converter

Decoder &

Error Correction

IO

Interface

High Resolution

Clock Phase Adj

Clock

Generator

I2C &

P-Port

LHC Bunch

Emulator

Configuration

Registers

Command Decoder

& Trigger

Logic

RX

TX

Parallel/Serial

Converter

Encoder

& FEC

IO

Interface

Laser Diode

Self Test

Logic

JTAG

Slave

SEU monitor

& Correct

Watchdog

& Init Logic

Cable

Needs 3*logic + Voting

GBT


Prototypes

Prototypes

  • Three GBT building blocks were prototyped in 130 nm CMOS:

    • Laser driver (Gianni Mazza, INFN Torino)

    • Encoder / decoder (Giulia Papotti, CERN)

    • Limiting Amplifier (Paulo Moreira, CERN)

  • Tape out in December 2005

  • Dice received in March 2006

  • Two of the circuits already successfully tested:

    • Encoder / decoder

    • Limiting Amplifier

GBT


Encoder

control

resetn

data_e_strb

data enable

clock

hold

load

resetn

enable

enable

ser data

ser start

scr enable

data loaded[0]

synch out

resetn

80

data register

8

64

demux

data loaded[2]

scrd out

scr data in

64

64

to be ser

80

data out

IDLE

scrambler

bypassRS

serializer

64

to be encoded

64

80

encoded 80

bypass scr

RS enc

scr on

64

scrd idle

80

ser data in

RS on

80

64

Encoder

GBT


Decoder

control

resetn

data_d_strb

clock

data/idle

rs load

rs hold

copy sr

rs enable

des resetn

data frame

frame sync

des enable

mux resetn

mux enable

data to decode[0]

data to decode[2]

synch in

error

shift register

rs input

80

64

dec whole

frame

synch

RS dec

scr out

80

64

64

64

scrd in

RS on dec out

idle for scr 1

idle for scr 2

data out

descr.

data in

mux word in

80

64

8

data dec out

RS/scr bridge

64

64

64

bypass scr

mux

64

64

bypassRS 1

bypassRS 2

64

64

64

fs on

scr on

RS on

Decoder

GBT


Limiting amplifier

Limiting Amplifier

  • Specifications:

  • Data rate: 3.60 Gbit/s

  • Gain: > 55 dB

  • Bandwidth > 2.52 GHz

  • Equivalent input noise: < 1 mV

  • Minimum input signal (differential): 10 mV

  • Maximum input signal (differential): 600 mV

GBT


Limiting amplifier1

Limiting Amplifier

Gain

Cell

Gain

Cell

Gain

Cell

Bias

Gain

Cell

OffsetCancellation

Output Buffer

Size: 194 mm × 194 mm

GBT


Limiting amplifier2

Limiting Amplifier

3.35 Gbit/s

1 Gbit/s

GBT


Summary

Summary

  • We propose a Single ASIC solution for:

    • Trigger Links;

    • Data Acquisition Links;

    • Slow Control Links.

  • For TTC applications we try to eliminate the drawbacks of the previous system:

    • The link becomes bidirectional;

    • Allows execution of complex commands in a single bunch crossing interval;

    • Trigger Decisions as well as data become protected against SEUs.

  • The system allows flexible link topologies

  • Specifications are still evolving for which we need the feedback of the potential users

  • Some of the building blocks of the transceiver are “universal” and for some of them we have already attempted practical implementations:

    • Laser driver

    • Encoder/decoder: Line code and CRC

    • Limiting amplifier

GBT


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