Time Protocols in NUSTAR

Time Protocols refer to various ways to synchronise and distribute clock and timestamp information to the many DAQ systems within NUSTAR.

The gold standard and ideal solution is White Rabbit, which also provides timing to the GSI and FAIR accelerators.
More information on White Rabbit in this context is available at: https://wiki.gsi.de/TOS/Timing/WebHome

For DAQ use, White Rabbit specifies a 125 MHz clock with "low ns" timestamp accuracy (1 ns resolution) and "low ps" jitter of the clock edge.
I.e, a system using a White Rabbit-derived clock has a "low ps" absolute time, see pages 78-81: https://www.gsi.de/fileadmin/EE/MBS/mbs_overview.pdf
NUSTAR DAQs can connect to the White Rabbit network at GSI with approved receivers: VETAR (VME), PEXARIA (PCIe) and WR-EXPLODER (Standalone).

For DAQs that cannot use an approved receiver directly, various other protocols are used to transmit the WR (potentially at reduced quality). A summary table is shown below.

Additional detail is provided in the attached slides: time_protocols.odp time_protocols.pdf

Protocol	DC Bal	PLL	Medium	Transmit	Receive	Encoding	Record	Rate	WRTCLK	Future
White Rabbit	Y	Y	Single-Mode Fiber	WR Xmitter	WR Receiver	Ethernet 8b10b		1.25 GHz		Reference time
Ratatime	Y	N	Any*	FPGA	FPGA	Self-aligning Pattern		1-10 MHz	Out	Deprecate
Heimtime	N	N	Any*	FPGA	PC Complex	Periodic+Data	Y	200-400 Hz Varying	Out	Deprecate
Rataclock PLL	Y	Y	Any*	FPGA	FPGA	PWM Clock		> 5 MHz	Out
Rataclock Slow	Y	Y?	Any*	FPGA WR-LM32	FPGA	PWM Clock		1-10 MHz	Out
Heimtime II			Any*	FPGA WR-LM32	PC FPGA	Periodic+Data	Y	10 Hz-100 kHz		FPGA Version
Clock + "Schakel"	Y+N	Y	2x LVDS	FPGA	FPGA	Clock + Time Data		Clock: 200 MHz Timestamp: 50 MHz@100 kHz	In
Clock + Reset	N	Y	2x Any*	(FPGA)	(FPGA)	Clock Reset				Not Timing DO NOT USE

Any* = Arbitrary digital I/O of suitable speed: NIM, ECL, LVDS, etc
DC Balanced: Constant DC average (0 and 1 equal over a long time)
PLL: Clock recovery via PLL
Transmit: Code to transmit, WM-LM32 is softcore in WR modules
Receive: Code for receiver
Record: Can be recorded in DAQ channel (low rate)
Rate: Approx. signal rate/required bandwidth
WRTCLK: Handled by WRTCLK Gateware

Ratatime description (see "Serial timestamp distribution"): https://fy.chalmers.se/~f96hajo/trloii/vulom4_trlo/description.html
(Old) Heimtime description: (see "Heimtime (speaking clock) sender"): https://fy.chalmers.se/~f96hajo/trloii/vulom4_trlo/description.html
Rataclock description: https://fy.chalmers.se/~f96hajo/rataser/

-- NicolasHubbard - 2026-01-16