What is the Treadle
Treadle is a hardware circuit simulator that takes its circuit description directly from FIRRTL. It is based on earlier work done in the FirrtlInterpreter. Treadle is most commonly used as a backend for ChiselTest and ChiselTesters unit tests framework. It supports a Peek, Poke, Expect, Step interface. Treadle can be quite a bit slower for very large circuits but it spins up much faster than other backends so for unit tests of small to medium circuits it generally runs considerably faster.
Treadle also provides the TreadleRepl, an interactive shell that provides execution and debugging commands.