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OpenTDC

Intro

OpenTDC is a Time to Digital Converter (TDC) and a Fine Delay (FD) design.

The TDC can timestamp a pulse with a precision below 1 ns, while the FD can generate a pulse with the same precision.

TDC could be used to measure distances using time-of-flight of laser pulses. It is also used to measure the time-of-flight of particules in High Energy Physic experiments. A TDC could also be used in LIDAR.

The first implementation aims at providing a very simple TDC+FD implementation (based only on standard cells) and to test different cell libraries, different delay elements and different layouts. We will evaluate stability over time, power consumption and accuracy (all of them are difficult to estimate using analog simulators). This first implementation could also be used by other people to (partially) characterize the standard libraries.

It is forseen in a next implementation to add a FIFOs to handle pulse bursts, add a logic to convert row results (number of taps) to a time value and to be able to mesure pulse width. It is also forseen to improve handling to clock lines, and maybe to design a delay element.

You can also read the blog in the repository that tells about the progress of this project.

Particularities of the design:

  • Mixes different cell libraries (hd, hs)
  • Tool generated macros
  • Macros within macros
  • mixed languages (VHDL and verilog)

License

The design license is Apache 2.0. There is no third-party sources, the design is self-contained.

Building

First generate the hard macros in an OpenLANE docker shell:

  make macros

As most of the sources are in VHDL, you then need to synthesis them and generate very simple verilog. This verilog will be the source for OpenLANE. This is done with the ghdl-yosys-plugin.

  make verilog

Start an OpenLANE docker shell and harden the design:

  make gds/user_project_wrapper.gds

Testing

There are functional unit tests in tb/.

And a simple integration test with caraval in tests/.

Global Architecture

Each TDC or FD is within a macro, which is connected to the wishbone bus either through the main block wb_interface or through an extender wb_extender (which is connected to the main block).

In addition, there is one TDC and one FD in the main block.

And finally, there is an independant rescue block which contains one TDC and one FD and connected to the logical analyzer interface.

Register map

Not documented outside the source files! But each device uses 8 words. A device is either a TDC or a FD, except device 0 which is a control device. You can identify a device by reading at offset 0x1c. See tdc core and fd core source files for the registers, and wb_interface for the main controller.

Contributing

Please use issues and pull-requests from github