82a142b14c
Here's a high-level overview of what this commit does: - Compiles Sail into SystemVerilog including patchin compiler bugs - Create a TCL file that tells JasperGold what to prove and assume - Check memory operations modelling the LSU Most of these properties now prove without time-bound on the response from memory due to alternative LSUs - Check memory even with Smepmp errors: Continues on top of https://github.com/riscv/sail-riscv/pull/196 - CSR verification - Checks for instruction types such as B-Type, I-Type, R-Type - Check illegal instructions and WFI instructions - Using psgen language for proof generation - Documentation on how to use the setup - Wrap around proof that proves instructions executed in a row still match the specification. - Liveness proof to guarantee instructions will retire within a upper bound of cycles. All of these proofs make heavy use of the concept of k-induction. All the different properties and steps are necessary to help the tool get the useful properties it needs to prove the next step. The instruction correctness, wrap-around and liveness all give us increased confidence that Ibex is trace-equivalent to Sail. Throughout this process an issue was found in Ibex where the pipeline was not flushing properly on changing PMP registers using clear: #2193 Alternative LSUs: This makes all top level memory properties prove quickly and at a low proof effort (1 or 2-induction). Three 'alternative LSUs' representing three stages of memory instructions: 1. Before the first response is received, in the EX stage 2. After the first response is received, but not the second grant, also in the EX stage 3. Before the last response is received in the WB stage. In each case we ask 'if the response came now, would the result be correct?'. Similar is applied for CSRs/PC though less directly. This is particularly interesting (read: ugly) in the case of a PMP error wbexc_exists makes Wrap properties fast to prove. The bottleneck becomes SpecPastNoWbexcPC, which fails only due to a bug. See the comment in riscv.proof. Co-authored-by: Marno van der Maas <mvdmaas+git@lowrisc.org> |
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| __init__.py | ||
| check_tool_requirements.core | ||
| CONTRIBUTING.md | ||
| CREDITS.md | ||
| ibex_configs.yaml | ||
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| ibex_icache.core | ||
| ibex_multdiv.core | ||
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| LICENSE | ||
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| NOTICE | ||
| python-requirements.txt | ||
| README.md | ||
| SECURITY.md | ||
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Ibex OpenTitan configuration Nightly Regression
Ibex RISC-V Core
Ibex is a production-quality open source 32-bit RISC-V CPU core written in SystemVerilog. The CPU core is heavily parametrizable and well suited for embedded control applications. Ibex is being extensively verified and has seen multiple tape-outs. Ibex supports the Integer (I) or Embedded (E), Integer Multiplication and Division (M), Compressed (C), and B (Bit Manipulation) extensions.
Ibex was initially developed as part of the PULP platform under the name "Zero-riscy", and has been contributed to lowRISC who maintains it and develops it further. It is under active development.
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 | 3.13 |
| Area - Yosys (kGE) | 16.85 | 26.60 | 32.48 | 66.02 |
| Area - Commercial (estimated kGE) | ~15 | ~24 | ~30 | ~61 |
| Verification status | Red | Green | Green | Green |
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.
- 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.
- v.1.0.0 of the RISC-V Bit-Manipulation Extension is supported as well as the remaining sub-extensions of draft v.0.93 of the bitmanip spec. The latter are not ratified and there may be changes before ratification. See Standards Compliance in the Ibex documentation for more information.
Documentation
The Ibex user manual can be
read online at ReadTheDocs. It is also contained in
the doc folder of this repository.
Examples
The Ibex repository includes Simple System. This is an intentionally simple integration of Ibex with a basic system that targets simulation. It is intended to provide an easy way to get bare metal binaries running on Ibex in simulation.
A more complete example can be found in the Ibex Demo System repository. In particular it includes a integration of the PULP RISC-V debug module. It targets the Arty A7 FPGA board from Digilent and supports debugging via OpenOCD and GDB over USB (no external JTAG probe required). The Ibex Demo System is maintained by lowRISC but is not an official part of Ibex.
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.