Adam Marmbrant Samuel Silverstein Stockholm University Link Test Status

2 Goals of study Explore several ideas:  Low-cost hardware?  10 Gbit ethernet vs. high speed FPGA I/O  Cheap FPGAs (Spartan 3)  Running links synchronously?  Use LHC bunch structure to schedule link retiming (comma chars) in empty BCs  Run from TTC clock  Commercial jitter cleaners sufficient?

3 Ribbon Fiber Simple transmitter (Zarlink ZL60113)  up to 12 channels  3.2 Gb/s  Low latency

4 Link board prototype (Stockholm) Readily available components  TI TLK3114SCZPV 10 Gb ENET transceivers  Xilinx XC3S1400AN-4 FPGA  National Semiconductor LMK03033CISQ clock conditioner Zarlink Tx 10 Gbit FPGA 10 Gbit 30 Gb/s 12-fiber bundle 96 x 320 Mb/s Zarlink Rx and/or or

5 Link prototype Tx Rx SNAP12 FPGA 10 GB TX/RX Jitter cleaner

6 Link prototype

7 Link test motherboard data out data in TTC fiber FPGA serial terminal TTCdec daughter card

8 Test setup

9 Current test setup Repeating sequence of parity-encoded data  Destination performs parity check One of three transceiver chips used so far (4 of 12 lanes) Simulated TTC optical signal from Spartan-5 developer board  Will also test with TTCvi crate  Using Deskew-1 output with PLL from TTCdec Link resynchronization during the large gap in LHC bunch structure

10 Current test setup 32-bit test sequence (24b + 8b checksum) Checksum tested at destination Data source Data sink 4 of 12 lanes currently populated

11 Test setup

12 Phase sweep of data clock ~800 ps

13 Timing-in "by design" CK0 CK90 CK180 CK270 Spartan3 DCM To pattern generator To I/O buffer multiplexers CKIN 160 MHz Works well in overnight runs

14 Results Long, stable runs with no parity errors!  17 hours  4 lanes  2.56 Gbit/s gives upper BER limit of 1.6e-15 Link very stable, very low realignment needed  Last week: 1500 seconds between realignment words without errors  Realignment takes fraction of a tick  two consecutive data words (rising, falling edges of 160 MHz clock)

15 Outlook Near-term plans  Run with all three transceivers (12 lanes)  Precise jitter measurements of conditoned TTC clock  Latency measurements between transmitting and receiving FPGAs  Run from "real" LHC clock hardware (TTCvi)

16 Conclusions Low cost hardware  10 Gbit ENET transceivers are relatively inexpensive and definitely usable in LHC environment.  Spartan 3 being used at its speed limit; we probably want a more modern device... Synchronous running possible  Resynching during one of the LHC bunch gaps is more than sufficient to maintain link Commercial clock conditioner can clean TTC clock well enough to run multi-GB links  Will do more careful measurements in near future