The 2014 Edition of VL is a "stable" fork of VL that is meant to provide continuing support for older tools, notably including esim, and also including other internal Centaur tools that are based on earlier versions of VL.
The 2014 Edition is not under active development. You should probably not use it for new projects, and it may be best to work toward eventually transitioning older tools away from it, in favor of the "main" version of vl.
Note that you can tell which version of VL you are using as follows.
Since each version uses its own package, it is possible to load both versions into the same ACL2 project simultaneously. This may be of use when transitioning code from the 2014 Edition to the main edition.
VL has a long history. Its development started in 2008. At that time, our goal was only to implement support for Verilog-2005. Over the next several years, we used VL to implement many tools, many of which were based around esim. ESIM is a purely bit-level backend.
In 2014, we began extending VL with features from SystemVerilog and also began work on a new, vector-level backend, sv. Throughout 2014, and into the start of 2015, we made substantial changes to VL and transitioned our internal projects to SV.
Much of this work was compatible with ESIM and expanded what the VL/ESIM
flow could handle. For instance: during this time, the ESIM flow gained better
support for ANSI-style ports, SystemVerilog style global parameters, basic
SystemVerilog idioms like
In February 2015, we began working on a substantial change to VL's expression representation. It became apparent that supporting ESIM through this change would require updating a large body of code. This would be a major cost to maintain code that we were no longer using.
In light of this, we decided that it was time to end support for the ESIM flow in VL, but we did not want to abandon ESIM altogether. As a compromise, we decided to create a stable fork of VL, based on the last version of VL that works with ESIM. This fork would allow older tools and proofs to continue to function, while giving us the freedom to move more quickly on the new versions of VL without having to continually update the ESIM flow.