# HDL workflow
This section describes the workflow and some best practices for developing
-the Libre-SoC hardware. We use nmigen, yosys and symbiyosys, and this
+the Libre-SOC hardware. We use nmigen, yosys and symbiyosys, and this
page is intended not just to help you get set up, it is intended to
help advise you of some tricks and practices that will help you become
effective team contributors.
and formal mathematical proofs for all code at all levels is therefore
paramount.
+Therefore, we need not only to be "self-sufficient" (absolutely under no circumstances critically reliant on somebody else's servers **or protocols**) we also need to ensure that everything (including all communication such as the mailing list archives) are recorded, replicable, and accessible in perpetuity. Use of slack or a "forum" either actively prevents or makes that much harder.
+
# Collaboration resources
The main message here: **use the right tool for the right job**.
* ftp server (<http://ftp.libre-riscv.org>): large file store.
we will add an IRC channel at some point when there are enough people
-to warrant having one.
+to warrant having one (and it will be publicly archived)
note also the lack of a "forum" in the above list. this is very deliberate. forums are a serious distraction when it comes to technical heavily goal-orientated development. recent internet users may enjoy looking up the "AOL metoo postings" meme.
using phone at airport flight soon, v. quick reply: ....")
* Always trim context but do not cut excessively to the point where people
cannot follow the discussion. Especially do not cut the attribution
- ("On monday xxx wrote")
+ ("On monday xxx wrote") of something that you are actually replying
+ to.
* Use inline replies i.e. reply at the point in the relevant part of
the conversation, as if you were actually having a conversation.
* Follow standard IETF reply formatting, using ">" for cascaded
"modern" GUI workflow or has access to the same computing resources as
you, so please do respect that.
+More on this concept is
+[here](https://www.linuxjournal.com/content/line-length-limits).
+Note *very pointedly* that Linus Torvalds *specifically* states that
+he does not want Linux kernel development to become the exclusive
+domain of the "wealthy". That means **no** to assumptions about
+access to ultra-high resolution screens.
+
# Software prerequisites
Whilst many resources online advocate "sudo" in front of all root-level
* apt-get install build-essential
* apt-get install git python3.7 python3.7-dev python-nosetest3
* apt-get install graphviz xdot gtkwave
+* apt-get install python3-venv
+* apt-get install python-virtualenv # this is an alternative to python3-venv
* return to user prompt (ctrl-d)
This will get you python3 and other tools that are needed. graphviz is
essential for showing the interconnections between cells, and gtkwave
is essential for debugging.
+If you would like to save yourself a lot more typing, check out the
+[dev-env-setup](https://git.libre-soc.org/?p=dev-env-setup.git;a=summary)
+repository, examine the scripts there and use them to automate much of
+the process below.
+
## git
Look up good tutorials on how to use git effectively. There are so many
Follow the source code (git clone) instructions here:
<http://www.clifford.at/yosys/download.html>
-Do not try to use a fixed revision (currently 0.9), nmigen is evolving
-and frequently interacts with yosys
+Or, alternatively, use the
+[yosys-et-al](https://git.libre-soc.org/?p=dev-env-setup.git;a=blob;f=yosys-et-al;hb=HEAD)
+script (which also installs symbiyosys and its dependencies)
+
+Do not try to use a fixed revision of yosys (currently 0.9), nmigen is evolving
+and frequently interacts with yosys.
## symbiyosys
* mkdir ~/src
* cd !$
-* git clone https://github.com/m-labs/nmigen.git
+* git clone https://github.com/nmigen/nmigen.git
* cd nmigen
* sudo bash
* python3 setup.py develop
## Softfloat and sfpy
These are a test suite dependency for the ieee754fpu library, and
-will be changed in the future to use Jacob's algorithmic numeric
+will be changed in the future to use Jacob's [simple-soft-float](https://crates.io/crates/simple-soft-float)
library. In the meantime, sfpy can be built as follows:
git clone --recursive https://github.com/billzorn/sfpy.git
git apply /path/to/ieee754fpu/berkeley-softfloat.patch
cd ..
- # install dependencies
+ # prepare a virtual environment for building
python3 -m venv .env
- . .env/bin/activate
+
+ # or, if you prefer the old way:
+ # virtualenv -p python3 .env
+
+ # install dependencies
+ source .env/bin/activate
pip3 install --upgrade -r requirements.txt
# build
It should print out `Posit8(1.3125)`
+## qemu, cross-compilers, gdb
+
+As we are doing POWER ISA, POWER ISA compilers, toolchains and
+emulators are required.
+
+Install powerpc64 gcc:
+
+ apt-get install gcc-9-powerpc64-linux-gnu
+
+Install qemu:
+
+ apt-get install qemu-system-ppc
+
+Install gdb from source. Obtain the latest tarball, unpack it, then:
+
+ cd gdb-9.1 (or other location)
+ mkdir build
+ cd build
+ ../configure --srcdir=.. --host=x86_64-linux --target=powerpc64-linux-gnu
+ make -j16
+ make install
+
## Coriolis2
See [[coriolis2]] page, for those people doing layout work.
avoid this kind of thing however pair-programming is difficult to organise
for remote collaborative libre projects (suggestions welcomed here)
+### Enable editor auto-detection of file changes by external programs
+
+This is important. "git pull" will merge in changes. If you then
+arbitrarily save a file without re-loading it, you risk destroying
+other people's work.
+
### Absolutely no auto-generated output
* **do not commit autogenerated output**. write a shell script and commit
### Do not break existing code
-* keep working code working **at all times**. find ways to ensure that this is the case. examples include writing alternative classes that replace existing functionality and adding runtime optiobs to select between old and new code.
+* keep working code working **at all times**. find ways to ensure that this is the case. examples include writing alternative classes that replace existing functionality and adding runtime options to select between old and new code.
### Small commits with relevant commit message
### Why such strict rules?
-the reason for all the above is because python is a weakly typed language.
+the reason for all the above is because python is a dynamically typed language.
make one tiny change at the base level of the class hierarchy and the
effect may be disastrous.
causes unnecessary resource utilisation, makes code readability and
tracking extremely difficult, and results in unintended side-effects.
+example: often you want to find the code from which a class was imported.
+nirmally you go to the top of the file, check the imports, and you know
+exactly which file has the class because of the import path. by using
+wildcards, you have absolutely *no clue* which wildcard imported which
+class or classes.
+
+example: sometimes you may accidentally have duplicate code maintained
+in two or more places. editing one of them you find, puzzlingly, that
+the code behaves in some files with the old behaviour, but in others it
+works. after a nassive amount of investigation, you find that the working
+files happen to have a wildcard import of the newer accidental duplicate
+class **after** the wildcard import of the older class with exactly the
+same name. if you had used explicit imports, you would have spotted
+the double import of the class from two separate locations, immediately.
+
+really. don't. use. wildcards.
+
### Keep file and variables short but clear
* try to keep both filenames and variable names short but not ridiculously
m.d.comb" followed by multiple "comb += nmigen_stmt" lines is a good trick
that can reduce code indentation by 6 characters without reducing clarity.
+Additionally, use comments just above an obtuse variable in order to
+help explain what it is for. In combination with keeping the the module
+itself short, other readers will not need to scroll back several pages
+in order to understand the code.
+
+Yes it is tempting to actually use the variables as
+self-explanatory-comments and generally this can be extremely good
+practice. the problem comes when the variable is so long that a function
+with several parameters csn no longer fit on a single line, and takes
+up five to ten lines rather than one or two. at that point, the length
+of the code is adversely affected and thus so is readability by forcing
+readers to scroll through reams of pages.
+
+it is a tricky balance: basically use your common sense, or just ask
+someone else, "can you understand this code?"
+
### Reasons for code structure
regarding code structure: we decided to go with small modules that are
## Unit tests
+For further reading, see the wikipedia page on
+[Test-driven Development](https://en.wikipedia.org/wiki/Test-driven_development)
+
This deserves its own special section. It is extremely important to
appreciate that without unit tests, python projects are simply unviable.
Python itself has over 25,000 individual tests.
black art. This is where team collaboration particularly kicks in,
so if you need help, ask on the mailing list.
+## Don't comment out unit tests: add them first (as failures) and fix code later
+
+Unit tests serve an additional critical purpose of keeping track of code
+that needs to be written. In many cases, you write the unit test *first*,
+despite knowing full well that the code doesn't even exist or is completely
+broken. The unit test then serves as a constant and important reminder
+to actually fix (or write) the code.
+
+Therefore, *do not* comment out unit tests just because they "don't work".
+If you absolutely must stop a unit test from running, **do not delete it**.
+Simply mark it with an appropriate
+["skip" decorator](https://docs.python.org/3/library/unittest.html#skipping-tests-and-expected-failures),
+preferably with a link to a URL in the [bugtracker](http://bugs.libre-riscv.org)
+with further details as to why the unit test should not be run.
+
# TODO Tutorials
Find appropriate tutorials for nmigen and yosys, as well as symbiyosys.
+* Robert Baruch's nmigen tutorials look really good:
+ <https://github.com/RobertBaruch/nmigen-tutorial>
* Although a verilog example this is very useful to do
<https://symbiyosys.readthedocs.io/en/latest/quickstart.html#first-step-a-simple-bmc-example>
* This tutorial looks pretty good and will get you started
* There exist several nmigen examples which are also executable
<https://github.com/m-labs/nmigen/tree/master/examples/> exactly as
described in the above tutorial (python3 filename.py -h)
+
projects / libreriscv.git / blobdiff