bazel-verilog-test

Automated builds are executed on each PR, and once a week even if no code changed the week prior.

Testing verilog build rules from https://github.com/hdl/bazel_rules_hdl

This is the answer to the question posed at: hdl/bazel_rules_hdl#123

Troubleshooting

I intend to keep this repository in working order. If something does not work, file a bug.

Prerequisites

This is a prep-work checklist to be able to compile the code in this repo with success. I hope you will find it quite modest.

Bazelisk

Download and install bazelisk (not bazel) following the instructions.

When you download the appropriate version for your system, place it somewhere in your $PATH, and name it bazel. This will give you a command-for-command compatible bazel binary, with the added bonus that it will download the exact bazel binary version that each project needs. This is of big help when dealing with various projects that use bazel.

I recommend using bazelisk instead of bazel wherever you can, and installing it under the binary name bazel in your $PATH, always.

From here on I will assume that you did as advised in the prerequisites.

Doing things

Now that you installed the needed tools, we can try some examples out. bazel will download any needed libraries the first time you run it, so give it some time.

Clone this repository

git clone https://github.com/filmil/bazel-verilog-test
cd bazel-verilog-test  # to go to the directory you just cloned

Build the example

bazel build //:counter_place_and_route

After a considerable amount of time spent in downloading and compiling the prerequisites, you should have your placed and routed design.

What needed resolving

Somewhat surprisingly, the bazel_rules_hdl repository does not show a functional example of using the repository rules. The example given in the README.md is not only incorrect, but also incomplete. Substantial additions are needed to go from that example to this repository. See the list below.

This is a short list of things that needed resolving to get this working repo up and running. With all of that fixed, I was able to build the sample basic design without errors.

• The repository rules at https://github.com/hdl/bazel_rules_hdl are sensitive to bazel version. This has to do with the backwards incompatible evolution of @bazel_tools but also the approaches the prerequisite deps are taking to bazel compilation. I tried to fix the HDL rules at top of tree, but could not do that easily. To resolve this issue, I added .bazelversion at the project root and pegged the bazel version needed.

• This, in turn, means that the best way to compile this repository is by using bazelisk. bazelisk will read .bazelversion and automatically download and apply the appropriate bazel version to your repository.

• The README.md in the bazel_rules_hdl repository is lacking a sample working set of git hash and sha_256, and has no clear instruction to choose a working set. It is also offering a syntactically incorrect WORKSPACE example, which one should also work around.

• The WORKSPACE file example in the repository is also lacking some needed declarations. I supplanted those based on the WORKSPACE file in bazel_rules_hdl, and the observations given in hdl/bazel_rules_hdl#123.

• The repository is not complete with a set of carefully placed .bazelrc directives. This is not mentioned in README.md, but is required for the build to work. At minimum, the dependency code requires C++17 or higher, which you don't get by default.

• I added a hermetic python interpreter configuration to the WORKSPACE file, so you don't need to worry about having the correct python interpreter for the project.

Example output

This is what my computer printed when I built the example counter. Compilation was quick because I already spent a long time compiling the prerequisites, and this was at least the second time I ran it. The first time around, your output will be significantly more wordy.

$ bazel build //:counter_place_and_route
INFO: Analyzed target //:counter_place_and_route (23 packages loaded, 10985 targets configured).
INFO: Found 1 target...
Target //:counter_place_and_route up-to-date:
  bazel-bin/counter_place_and_route_detail_routed.def
  bazel-bin/counter_place_and_route__detailed_routing.db
  bazel-bin/counter_place_and_route__floorplan.log
  bazel-bin/counter_place_and_route__place_pins.log
  bazel-bin/counter_place_and_route__pdn_generation.log
  bazel-bin/counter_place_and_route__global_placement.log
  bazel-bin/counter_place_and_route__resizing.log
  bazel-bin/counter_place_and_route__clock_tree_synthesis.log
  bazel-bin/counter_place_and_route__global_routing.log
  bazel-bin/counter_place_and_route__detailed_routing.log
  bazel-bin/counter_place_and_route_verilog_based_power_results.textproto
  bazel-bin/counter_place_and_route_verilog_based_area_results.textproto
  bazel-bin/counter_place_and_route_general_routing_power_results.textproto
  bazel-bin/counter_place_and_route_general_routing_area_results.textproto
  bazel-bin/counter_place_and_route_commands.tcl
INFO: Elapsed time: 4.611s, Critical Path: 0.09s
INFO: 1 process: 1 internal.
INFO: Build completed successfully, 1 total action