FPGA link

Warning

The reference design and the on-the-wire format are not stable and will be subject to incompatible changes with further development.

The FPGA link output of the Time Tagger X allows you to connect an FPGA of your own design to the Time Tagger X via an Ethernet-based protocol and benefit from higher data throughput and lower latency compared to USB.

In a typical use case, you want to use either process tags at a higher rate than the USB connection to the PC allows or integrate the measurements into a test fixture and trigger events based on the measurements.

The SFP+ port on the Time Tagger X can be used either with a DAC or fiber transceivers to connect to your own FPGA. We recommend using the OpalKelly XEM8320 for your custom design.

The QSFP+ port on the Time Tagger X should be used with a fiber transceiver to connect to your own FPGA. We also recommend using the OpalKelly XEM8320 together with the SZG-QSFP for your custom design.

Note

We recommend using the SFP+ port unless the higher bandwidth is necessary.

Warning

There is currently no retransmission support so if corruption occurs during transmission, tags will be permanently lost. Please verify that your data link is of high quality or that tag loss can be tolerated.

Getting Started with SFP+

To enable the FPGA link output of the Time Tagger use enableFpgaLink(). Start by enabling the FPGA link on channel 1:

import TimeTagger
tagger = TimeTagger.createTimeTagger()
tagger.enableFpgaLink([1], "", TimeTagger.FpgaLinkInterface.SFPP_10GE, True)

To receive the tags, use our Time Tagger FPGA link reference design. Follow the instructions in the XEM8320 readme to build the reference design. Connect the SFP+ port on the Time Tagger X to the SFP 1 port on the XEM8320 and load the bitstream on the XEM8320. You should now be able to observe the LED D1 on the XEM8320 matching the input state on channel 1 of the Time Tagger X.

To verify the link quality, activate a test signal as follows:

tagger.setTestSignal([1], True)

and reload the bitstream on the XEM8320. LED D6 should stay dark, indicating that the channel 1 events are arriving at the expected time without drops.

Using QSFP+

QSFP+ is quite similar to using SFP+. Start by enabling the FPGA link for the QSFP+ interface for input channel 1 of the Time Tagger X:

import TimeTagger
tagger = TimeTagger.createTimeTagger()
tagger.enableFpgaLink([1], "", TimeTagger.FpgaLinkInterface.QSFPP_40GE, True)

Similarly use our Time Tagger FPGA link reference design, but follow the instructions in the [40G readme](https://github.com/swabianinstruments/TimeTagger-FPGALink-Reference/tree/main/target/opalkelly-xem8320-qsfp).

Connect the QSFP+ port of the Time Tagger X with the SZG-QSFP module which has to be connected to Port E of the XEM8320. You should now be able to observe the LED D1 on the XEM8320 matching the input state on channel 1 of the Time Tagger X.

Note

Using the reference design with QSFP+ requires the Xilinx EF-DI-LAUI-SITE IP core license. We recommend starting with the SFP+ connection.

Warning

Only one output is active at the same time. Enabling the QSFP+ port disables the SFP+ port and vice-versa.

Modifying the reference design

Follow the instructions in Building you own design.