505d33b35a
This patch adds IEEE-1800 compliant scheduling support for the Inactive scheduling region used for #0 delays. Implementing this requires that **all** IEEE-1800 active region events are placed in the internal 'act' section. This has simulation performance implications. It prevents some optimizations (e.g. V3LifePost), which reduces single threaded performance. It also reduces the available work and parallelism in the internal 'nba' section, which reduced the effectiveness of multi-threading severely. Performance impact on RTLMeter when using scheduling adjusted to support proper #0 delays is ~10-20% slowdown in single-threaded mode, and ~100% (2x slower) with --threads 4. To avoid paying this performance penalty unconditionally, the scheduling is only adjusted if either: 1. The input contains a statically known #0 delay 2. The input contains a variable #x delay unknown at compile time If no #0 is present, but #x variable delays are, a ZERODLY warning is issued advising the use of '--no-sched-zero-delay' which is a promise by the user that none of the variable delays will evaluate to a zero delay at run-time. This warning is turned off if '--sched-zero-delay' is explicitly given. This is similar to the '--timing' option. If '--no-sched-zero-delay' was used at compile time, then executing a zero delay will fail at runtime. A ZERODLY warning is also issued if a static #0 if found, but the user specified '--no-sched-zero-delay'. In this case the scheduling is not adjusted to support #0, so executing it will fail at runtime. Presumably the user knows it won't be executed. The intended behaviour with all this is the following: No #0, no #var in the design (#constant is OK) -> Same as current behaviour, scheduling not adjusted, same code generated as before Has static #0 and '--no-sched-zero-delay' is NOT given: -> No warnings, scheduling adjusted so it just works, runs slow Has static #0 and '--no-sched-zero-delay' is given: -> ZERODLY on the #0, scheduling not adjusted, fails at runtime if hit No static #0, but has #var and no option is given: -> ZERODLY on the #var advising use of '--no-sched-zero-delay' or '--sched-zero-delay' (similar to '--timing'), scheduling adjusted assuming it can be a zero delay and it just works No static #0, but has #var and '--no-sched-zero-delay' is given: -> No warning, scheduling not adjusted, fails at runtime if zero delay No static #0, but has #var and '--sched-zero-delay' is given: -> No warning, scheduling adjusted so it just works |
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| _static | ||
| bin | ||
| gen | ||
| guide | ||
| .gitignore | ||
| CONTRIBUTING.rst | ||
| CONTRIBUTORS | ||
| Makefile | ||
| README.rst | ||
| internals.rst | ||
| security.rst | ||
| spelling.txt | ||
| verilated.dox | ||
README.rst
.. SPDX-FileCopyrightText: 2003-2026 Wilson Snyder .. SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0 Verilator Documentation ======================= This folder contains sources for Verilator documentation. For formatted documentation see: - `Verilator README <https://github.com/verilator/verilator>`_ - `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>`_