25fde8fcb3
This makes changes to support Cadence Xcelium 20.09.001. Cadence recommends that disabling forks should be done using a "disable fork;" statement, not the "disable fork_process_label;" construct. The "disable fork_process_label" construct for forks is not defined in the IEEE Std 1800-2017 LRM. See section 9.6.2 of the LRM (2017). For a more detailed explanation, please see the description from my colleague in Issue #1174: https://github.com/lowRISC/ibex/issues/1174. In many cases, Xcelium will ignore a disable statement if it is not in the "disable fork;" form. This causes problems in many tests, most notably in the riscv_reset_test. Processes not being disabled when reset is asserted cause not just test failures, but the entire regression to crash. Most changes here are simple substitutes of "disable fork;" where "disable label;" was. Some changes in core_ibex_test_lib.sv require the layout of the fork to be adjusted. Signed-off-by: CathalMCrevinn <cathal_minnock@crevinn.com> |
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| ci | ||
| doc | ||
| dv | ||
| examples | ||
| formal | ||
| lint | ||
| rtl | ||
| shared | ||
| syn | ||
| util | ||
| vendor | ||
| .clang-format | ||
| .gitignore | ||
| .svlint.toml | ||
| azure-pipelines.yml | ||
| check_tool_requirements.core | ||
| CONTRIBUTING.md | ||
| CREDITS.md | ||
| ibex_configs.yaml | ||
| ibex_core.core | ||
| ibex_core_tracing.core | ||
| ibex_icache.core | ||
| ibex_multdiv.core | ||
| ibex_pkg.core | ||
| ibex_tracer.core | ||
| LICENSE | ||
| Makefile | ||
| python-requirements.txt | ||
| README.md | ||
| src_files.yml | ||
| tool_requirements.py | ||
Ibex RISC-V Core
Ibex is a small and efficient, 32-bit, in-order RISC-V core with a 2-stage pipeline that implements the RV32IMC instruction set architecture.
This core was initially developed as part of the PULP platform under the name "Zero-riscy" [1], and has been contributed to lowRISC who maintains it and develops it further. It is under active development, with further code cleanups, feature additions, and test and verification planned for the future.
Configuration
Ibex offers several configuration parameters to meet the needs of various application scenarios. The options include different choices for the architecture of the multiplier unit, as well as a range of performance and security features. The table below indicates performance, area and verification status for a few selected configurations. These are configurations on which lowRISC is focusing for performance evaluation and design verification (see supported configs).
| Config | "micro" | "small" | "maxperf" | "maxperf-pmp-bmfull" |
|---|---|---|---|---|
| Features | RV32EC | RV32IMC, 3 cycle mult | RV32IMC, 1 cycle mult, Branch target ALU, Writeback stage | RV32IMCB, 1 cycle mult, Branch target ALU, Writeback stage, 16 PMP regions |
| Performance (CoreMark/MHz) | 0.904 | 2.47 | 3.13 | 3.05 |
| Area - Yosys (kGE) | 17.44 | 26.06 | 35.64 | 58.74 |
| Area - Commercial (estimated kGE) | ~16 | ~24 | ~33 | ~54 |
| Verification status | Red | Green | Amber | Amber |
Notes:
- Performance numbers are based on CoreMark running on the Ibex Simple System platform.
Note that different ISAs (use of B and C extensions) give the best results for different configurations.
See the Benchmarks README for more information.
The "maxperf-pmp-bmfull" configuration sets a
SpecBranchparameter inibex_core.sv; this helps timing but has a small negative performance impact. - Yosys synthesis area numbers are based on the Ibex basic synthesis flow using the latch-based register file.
- Commercial synthesis area numbers are a rough estimate of what might be achievable with a commercial synthesis flow and technology library.
- For comparison, the original "Zero-riscy" core yields an area of 23.14kGE using our Yosys synthesis flow.
- Verification status is a rough guide to the overall maturity of a particular configuration. Green indicates that verification is close to complete. Amber indicates that some verification has been performed, but the configuration is still experimental. Red indicates a configuration with minimal/no verification. Users must make their own assessment of verification readiness for any tapeout.
Documentation
The Ibex user manual can be
read online at ReadTheDocs. It is also contained in
the doc folder of this repository.
Contributing
We highly appreciate community contributions. To ease our work of reviewing your contributions, please:
- Create your own branch to commit your changes and then open a Pull Request.
- Split large contributions into smaller commits addressing individual changes or bug fixes. Do not mix unrelated changes into the same commit!
- Write meaningful commit messages. For more information, please check out the contribution guide.
- If asked to modify your changes, do fixup your commits and rebase your branch to maintain a clean history.
When contributing SystemVerilog source code, please try to be consistent and adhere to our Verilog coding style guide.
When contributing C or C++ source code, please try to adhere to the OpenTitan C++ coding style
guide.
All C and C++ code should be formatted with clang-format before committing.
Either run clang-format -i filename.cc or git clang-format on added files.
To get started, please check out the "Good First Issue" list.
Issues and Troubleshooting
If you find any problems or issues with Ibex or the documentation, please check out the issue tracker and create a new issue if your problem is not yet tracked.
Questions?
Do not hesitate to contact us, e.g., on our public Ibex channel on Zulip!
License
Unless otherwise noted, everything in this repository is covered by the Apache License, Version 2.0 (see LICENSE for full text).
Credits
Many people have contributed to Ibex through the years. Please have a look at the credits file and the commit history for more information.