Bazel on OpenROAD-flow-scripts(ORFS) with MegaBoom use case

Demonstrates a practical workflow for large designs in a git repository that is not a fork of OpenROAD-flow-scripts and that is using its own file layout: similar to a private repository or a large project.

MegaBoom(a RISC-V SoC from Chipyard) has been chosen as a test-case as it is large, familiar and interesting in itself.

Build and view result

The build of MegaBoom takes on the order of 24 hours, unless you configure an artifact server to download pre-built results.

To build BoomTile and set up scripts to view the results in the OpenROAD GUI:

bazel build BoomTile_final_gui

View result using Docker in OpenROAD GUI using the script that launches OpenROAD-flow-scripts make with the design configuration and forwards arguments to make to view the result:

bazel-bin/BoomTile_final_docker gui_final

Setup

For running Bazel flow for the ORFS, MegaBoom uses bazel-orfs. It provides two different Bazel flows for running Physical Design Flow with OpenROAD-flow-scripts. For the installation and usage guide, please refer to bazel-orfs's README.

Bazel-orfs must be specified in MegaBoom as the external dependency. It can be pinned to a specific revision of the upstream repository or the dependency can point to a local bazel-orfs workspace available on disk. Setup can be modified in MODULE.bazel file.

Using the OpenROAD project Bazel artifact server to download pre-built results

If you only have a single Google account that you use for Google Cloud locally, you can use --google_default_credentials.

If you are use multiple google accounts, using the default credentials can be cumbersome when switching between projects. To avoid this, you can use the --credential_helper option instead, and pass a script that fetches credentials for the account you want to use. This account needs to have logged in using gcloud auth login and have access to the bucket specified.

To use this feature, copy the snippet below into .bazelrc and specify your username by modifying # user: myname@openroad.tools:

# user: myname@openroad.tools
build --credential_helper=%workspace%/cred_helper.py --remote_cache=https://storage.googleapis.com/megaboom-bazel-artifacts --remote_cache_compression=true

cred_helper.py will parse .bazelrc and look for the username in the comment.

Note: To test the credential helper, make sure to restart Bazel to avoid using a previous cached authorization:

bazel shutdown
bazel build BoomTile_final_scripts

To gain access to the https://storage.googleapis.com/megaboom-bazel-artifacts bucket, reach out to Tom Spyrou, Precision Innovations (https://www.linkedin.com/in/tomspyrou/).

About the MegaBoom RTL code

Based on: https://chipyard.readthedocs.io/en/stable/VLSI/Sky130-OpenROAD-Tutorial.html#initial-setup

Note: Chipyard main does not work smoothly with MegaBoom as of writing as Chipyard is mixing SFC and MFC.

Follow https://github.com/ucb-bar/chipyard/issues/1623 for latest updates.

That said, the rtl/ folder was generated using latest Chipyard + some hacked files locally:

make tutorial=sky130-openroad CONFIG=MegaBoomMacroConfig verilog

Hammer hacking with ASAP7

Build everything:

./build-setup.sh --skip-ctags --skip-conda --skip-toolchain --skip-firesim --skip-marshal --skip-clean

Create Verilog code:

make CONFIG=MegaBoomConfig tech_name=asap7 VLSI_TOP=ChipTop INPUT_CONFS=example-asap7.yml TOP_MACROCOMPILER_MODE='--mode synflops' verilog