upsilon/GUIDELINES.md

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# Firmware
See also [Dan Gisselquist][1]'s rules for FPGA development.
[1]: https://zipcpu.com/blog/2017/08/21/rules-for-newbies.html
* Use free and open source IP only. IP must be compatible with *both* the
GPL v3.0 and the CERN OHL-v2-S.
* Stick to Verilog 2005. F4PGA will accept SystemVerilog but yosys sometimes
synthesizes it incorrectly.
* Do not use parameters that are calculated from other parameters (yosys
will not parse them correctly). Use m4 macros instead.
* Do not use Verilog macros. Use m4.
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* Do all code and test generation in Makefiles.
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* Simulate *every* module, even the trivial ones using Verilator.
Simulation must be simulatable with open-source software (Verilator is
preferred, but Icarus Verilog and similar are fine). Put test code in the same
directory as the Verilog module, unless the Verilog module is external.
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* Synthesize and verify large modules independently on hardware using
the LiteX SoC generator. Put the generator source code (along with
the hardware test driver) in the repository.
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* Write *only* synthesizable verilog (except for direct test-bench code), even
for modules that will not be synthesized.
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* Dump traces using `.fst` format.
* Use only one clock.
* Only transition on the *positive edge* of the *system clock*.
* Do not use asynchronous resets.
* Don't write Wishbone bus code in Verilog modules. LiteX automatically
takes care of connecting modules together and assigning each register
a memory location.
* Keep all Verilog as generic as possible.
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* Always initialize registers.
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# Software
* Use free and open source libraries only. All libraries must be compatible
with the GNU GPL v3.0.
* Do not dynamically allocate memory.
* Use the [SEI CERT C Coding Standard][2] as a guideline.
* Use the [Linux kernel style guide][3] as a guideline (many parts of it
are not relevant for this project).
* Try to offload as much processing as possible to the computer.
[2]: https://wiki.sei.cmu.edu/confluence/display/c/SEI+CERT+C+Coding+Standard
[3]: https://www.kernel.org/doc/Documentation/process/coding-style.