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Krzysztof Bieganski
39af5d020e
Adds timing support to Verilator. It makes it possible to use delays,
event controls within processes (not just at the start), wait
statements, and forks.
Building a design with those constructs requires a compiler that
supports C++20 coroutines (GCC 10, Clang 5).
The basic idea is to have processes and tasks with delays/event controls
implemented as C++20 coroutines. This allows us to suspend and resume
them at any time.
There are five main runtime classes responsible for managing suspended
coroutines:
* `VlCoroutineHandle`, a wrapper over C++20's `std::coroutine_handle`
with move semantics and automatic cleanup.
* `VlDelayScheduler`, for coroutines suspended by delays. It resumes
them at a proper simulation time.
* `VlTriggerScheduler`, for coroutines suspended by event controls. It
resumes them if its corresponding trigger was set.
* `VlForkSync`, used for syncing `fork..join` and `fork..join_any`
blocks.
* `VlCoroutine`, the return type of all verilated coroutines. It allows
for suspending a stack of coroutines (normally, C++ coroutines are
stackless).
There is a new visitor in `V3Timing.cpp` which:
* scales delays according to the timescale,
* simplifies intra-assignment timing controls and net delays into
regular timing controls and assignments,
* simplifies wait statements into loops with event controls,
* marks processes and tasks with timing controls in them as
suspendable,
* creates delay, trigger scheduler, and fork sync variables,
* transforms timing controls and fork joins into C++ awaits
There are new functions in `V3SchedTiming.cpp` (used by `V3Sched.cpp`)
that integrate static scheduling with timing. This involves providing
external domains for variables, so that the necessary combinational
logic gets triggered after coroutine resumption, as well as statements
that need to be injected into the design eval function to perform this
resumption at the correct time.
There is also a function that transforms forked processes into separate
functions.
See the comments in `verilated_timing.h`, `verilated_timing.cpp`,
`V3Timing.cpp`, and `V3SchedTiming.cpp`, as well as the internals
documentation for more details.
Signed-off-by: Krzysztof Bieganski <[email protected]>
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Welcome to Verilator
====================
.. list-table::
* - **Welcome to Verilator, the fastest Verilog/SystemVerilog simulator.**
* Accepts Verilog or SystemVerilog
* Performs lint code-quality checks
* Compiles into multithreaded C++, or SystemC
* Creates XML to front-end your own tools
- |Logo|
* - |verilator multithreaded performance|
- **Fast**
* Outperforms many commercial simulators
* Single- and multi-threaded output models
* - **Widely Used**
* Wide industry and academic deployment
* Out-of-the-box support from Arm, and RISC-V vendor IP
- |verilator usage|
* - |verilator community|
- **Community Driven & Openly Licensed**
* Guided by the `CHIPS Alliance`_ and `Linux Foundation`_
* Open, and free as in both speech and beer
* More simulation for your verification budget
* - **Commercial Support Available**
* Commercial support contracts
* Design support contracts
* Enhancement contracts
- |verilator support|
What Verilator Does
===================
Verilator is invoked with parameters similar to GCC or Synopsys's VCS. It
"Verilates" the specified Verilog or SystemVerilog code by reading it,
performing lint checks, and optionally inserting assertion checks and
coverage-analysis points. It outputs single- or multi-threaded .cpp and .h
files, the "Verilated" code.
The user writes a little C++/SystemC wrapper file, which instantiates the
"Verilated" model of the user's top level module. These C++/SystemC files
are then compiled by a C++ compiler (gcc/clang/MSVC++). Executing the
resulting executable performs the design simulation. Verilator also
supports linking Verilated generated libraries, optionally encrypted, into
other simulators.
Verilator may not be the best choice if you are expecting a full featured
replacement for Incisive, ModelSim/Questa, VCS or another commercial
Verilog simulator, or if you are looking for a behavioral Verilog simulator
e.g. for a quick class project (we recommend `Icarus Verilog`_ for this.)
However, if you are looking for a path to migrate SystemVerilog to C++ or
SystemC, or your team is comfortable writing just a touch of C++ code,
Verilator is the tool for you.
Performance
===========
Verilator does not directly translate Verilog HDL to C++ or SystemC. Rather,
Verilator compiles your code into a much faster optimized and optionally
thread-partitioned model, which is in turn wrapped inside a C++/SystemC
module. The results are a compiled Verilog model that executes even on a
single-thread over 10x faster than standalone SystemC, and on a single
thread is about 100 times faster than interpreted Verilog simulators such
as `Icarus Verilog`_. Another 2-10x speedup might be gained from
multithreading (yielding 200-1000x total over interpreted simulators).
Verilator has typically similar or better performance versus the
closed-source Verilog simulators (Carbon Design Systems Carbonator,
Modelsim, Cadence Incisive/NC-Verilog, Synopsys VCS, VTOC, and Pragmatic
CVer/CVC). But, Verilator is open-sourced, so you can spend on computes
rather than licenses. Thus Verilator gives you the best cycles/dollar.
Installation & Documentation
============================
For more information:
- `Verilator installation and package directory structure
<https://verilator.org/install>`_
- `Verilator manual (HTML) <https://verilator.org/verilator_doc.html>`_,
or `Verilator manual (PDF) <https://verilator.org/verilator_doc.pdf>`_
- `Subscribe to verilator announcements
<https://github.com/verilator/verilator-announce>`_
- `Verilator forum <https://verilator.org/forum>`_
- `Verilator issues <https://verilator.org/issues>`_
Support
=======
Verilator is a community project, guided by the `CHIPS Alliance`_ under the
`Linux Foundation`_.
We appreciate and welcome your contributions in whatever form; please see
`Contributing to Verilator
<https://github.com/verilator/verilator/blob/master/docs/CONTRIBUTING.rst>`_.
Thanks to our `Contributors and Sponsors
<https://verilator.org/guide/latest/contributors.html>`_.
Verilator also supports and encourages commercial support models and
organizations; please see `Verilator Commercial Support
<https://verilator.org/verilator_commercial_support>`_.
Related Projects
================
- `GTKwave <http://gtkwave.sourceforge.net/>`_ - Waveform viewer for
Verilator traces.
- `Icarus Verilog`_ - Icarus is a full featured interpreted Verilog
simulator. If Verilator does not support your needs, perhaps Icarus may.
Open License
============
Verilator is Copyright 2003-2022 by Wilson Snyder. (Report bugs to
`Verilator Issues <https://verilator.org/issues>`_.)
Verilator is free software; you can redistribute it and/or modify it under
the terms of either the GNU Lesser General Public License Version 3 or the
Perl Artistic License Version 2.0. See the documentation for more details.
.. _CHIPS Alliance: https://chipsalliance.org
.. _Icarus Verilog: http://iverilog.icarus.com
.. _Linux Foundation: https://www.linuxfoundation.org
.. |Logo| image:: https://www.veripool.org/img/verilator_256_200_min.png
.. |verilator multithreaded performance| image:: https://www.veripool.org/img/verilator_multithreaded_performance_bg-min.png
.. |verilator usage| image:: https://www.veripool.org/img/verilator_usage_400x200-min.png
.. |verilator community| image:: https://www.veripool.org/img/verilator_community_400x125-min.png
.. |verilator support| image:: https://www.veripool.org/img/verilator_support_400x125-min.png