ROHD Hierarchy: an API for compact, generic traversal of a remote design

[desmonddak]

…pact, canonical addresses

Description & Motivation

It would be nice to have a hierarchy api that allows us to remotely traverse a design hierarchy using compact addressing to support a devtools-based debugger. For example, if we receive a dictionary of the design, we can communicate requests for more data from the design by using a compressed addressing scheme like (5th instance, 4th instance below that, 15th signal) to receive a set of data on that signal. If we need 1000s of simulation values, for example, we do not need to transmit all names, providing an order of magnitude savings in transmission bandwidth.

This capability allows us to incrementally a design view over multiple data requests. For now, we primarily have two: a 'slim' view, which is the full hierarchy with names, and then a full view, which is all connectivity. This can be extended to allow for a more incremental dictionary load to allow a remote agent to use limited memory to transit a very large design.

Related Issue(s)

None.

Testing

Tests are provided with a small design fixture using a new netlist format in JSON, equivalent to Yosys JSON. A future netlist synthesizer will provide design data nd this rohd_hierarchy adapter will allow us to communicate between remote agents.

Backwards-compatibility

Is this a breaking change that will not be backwards-compatible? If yes, how so?

No

Documentation

Does the change require any updates to documentation? If so, where? Are they included?

A README.md is included to describe the motivation, architecture, and key features of the api.