White Rabbit Inside

The D-TACQ ACQ2106 DAQ Appliance now supports White Rabbit the high precision network timing project initiated by CERN

White Rabbit (WR) provides extremely accurate timing on a standard fiber optic Ethernet link, with the possibility to work over long distances and large numbers of links. WR is an extension of IEEE1588 Precision Time Protocol

The ACQ2106 implementation is a complete port of White Rabbit Node functionality to the ZYNQ7030 SOC device on ACQ2106.

White Rabbit Ensures ..

• All nodes share a phase synchronized clock.
• All nodes share a TAI timestamp accurate to nanoseconds.

This is ideal for synchronizing D-TACQ networked DAQ appliances. Work by D-TACQ includes

• Port of the standard WR gateware to ZYNQ, compiled on a current version of Xilinx Vivado.
• Shared memory interface for parameter sharing (eg mac address, calibration constants) between the ZYNQ ARM core and the WRPC embedded core; eliminates the need for eeprom configuration storage.
• Use of the WR master clock to condition the local low jitter clock device already present on ACQ2106, allowing data acquisition modules to clock phase-synchronously at any frequency from 1 to 80MHz, integer Hz resolution.
• Use of WRTD / LXI wire protocol for sharing triggers. ACQ2106 can trigger a capture on an incoming control message packet from the WR network.
• Conventional External Triggers are snapshotted against the current TAI timestamp to a resolution of less than sample (12.5nsec mininum), and the receiving ACQ2106 can use this to multicast a trigger instruction to other ACQ2106 boxes on the network. All the units then start a capture completely simultaneously. The delay until start time has been tested reliable to less than 10 msec. This means that a WR enabled-cluster of ACQ2106 DAQ Appliances can be integrated into an existing plant without requiring any White Rabbit knowledge from the plant. If zero delay to trigger is required, then the cluster can run in pre/post mode, and "turn back time" at the end of the capture to the exact external trigger point.

The number of commercial White Rabbit node products is increasing. ACQ2106 enhances the ecosystem by providing

• High channel count high quality simultaneous Analog Inputs.
• High channel count simultaneous Analog Outputs and digital IO.

Use Cases

• WR-SLAVE: Isolated digitizer boxes are completely synchronized by remote master, without need for a dedicated connection.
• GROUP: A single ACQ2106 can convert a plant system trigger to TAI time and share this trigger with a cluster of ACQ2106 boxes. This can lead to extremely large systems eg 960 channels x 20MSPS in 20U, with no shared copper interconnect, giving a very high immunity to radiated noise.
• FUNCTION-TRIGGER: Units can generate a synthetic trigger based on DSP analysis of real time data. Multiple digitizers in a group can be running a Fault Monitor application - continuous capture with Analog Threshold Detect ATD trigger. The first box to detect a trigger broadcasts a stop time to the group. All systems run until the stop time, then wind back a preprogrammed delay time in the data buffer so that all units present a full rate pre/post data set centered on the declared trigger time.
• TRIGGER-GENERATOR: ACQ2106, in conjunction with digital IO module DIO482 together can generate a precise trigger pattern with preprogrammed relative delay. We anticipate that the whole sequence would be started on a TAI timestamp specified by an incoming Control Message Packet. ACQ2106 has two methods of running clocked digital outputs
  • Gate Pulse Generator GPG: the pattern is controlled from a hardware State Transition List. This is a very simple way to precisely control a sparse set of states over a period 0..100s. The total number of states is limited by hardware STL memory
  • Digital Pattern Generator DPG: here the output pattern is sourced as a raw data set in memory, typically played out at 4bytes x 1MHz. This is suitable for huge numbers of states. The pattern can become large of high sample rates (up to 25MHz) over long periods of time (to limit of memory).
• ARBITRARY-WAVEFORM-GENERATOR : ACQ2106 has a high channel count AWG function, typically running on 32 or 64 AO channels. This can be triggered by a remote WR control message packet.

What we have left to do

• Complete WRTD functionality, tracking the standard as it emerges.
• Reduce the trigger broadcast delay further.
• Run conventional Ethernet traffic on the WR ethernet port. Currently we run network traffic either on the regular 1000T (copper) port, or a separate 1000X SFP fiber optic port, but for lowest cost and simplest layout it would be helpful to combine time and data on the single WR fiber.

Product Demonstration planned at ICALEPCS 2019. Do visit our stand to see the great combination of precision ADC and precision network timing!.