Bazel-orfs

This repository contains Bazel rules for wrapping OpenROAD-flow-scripts (ORFS).

Why Bazel on top of ORFS?

bazel-orfs gives all the expected Bazel advantages to ORFS: artifacts, parallel builds, remote execution, repeatable builds, etc.

Also, ORFS and OpenROAD is work in progress and one should expect for large designs to get involved with the community or need a support contract with Precision Innovations (https://www.linkedin.com/in/tomspyrou/).

Using ORFS directly, instead of modifying it or creating an alternative flow, makes it easy to get the very latest features and version of OpenROAD and ORFS as well as having access to all ORFS features, including debugging features such as make issue and deltaDebug.py.

Since bazel-orfs uses the unmodified ORFS, it is easy to articulate familiar and easily actionable github issues for the OpenROAD and ORFS maintainers.

Requirements

• Bazelisk or Bazel - if using Bazel, please refer to .bazelversion file for the recommended version of the tool.

• Docker - Bazel utilizes Docker to set up the environment using ORFS artifacts from the container. The Docker image used in the flow defaults to openroad/orfs, with tag specified in the module file.

  NOTE: The bazel-orfs doesn't execute flows inside the Docker container, but rather uses the container as a source of ORFS artifacts.

• (Optional) Locally built ORFS. To use it, env.sh file from OpenROAD-flow-scripts has to be sourced or FLOW_HOME environment variable has to be set to the path of the local OpenROAD-flow-scripts/flow installation.

Usage

Core functionality is implemented as orfs_flow() Bazel macro in openroad.bzl file.

In order to use orfs_flow() macro in Bazel Workspace in other project it is required to use bazel-orfs as an external dependency through one of Bazel Module Methods:

• from git repository

  bazel_dep(name = "bazel-orfs")
  git_override(
      module_name = "bazel-orfs",
      remote = "<URL to bazel-orfs repository>",
      commit = "<git hash for specific bazel-orfs revision>",
  )

• from local directory

  bazel_dep(name = "bazel-orfs")
  local_path_override(
      module_name = "bazel-orfs",
      path = "<path to local bazel-orfs workspace>",
  )

The macro can now be placed in the BUILD file. The macro usage can look like this:

orfs_flow(
    name = "L1MetadataArray",
    abstract_stage = "route",
    macros = ["tag_array_64x184_generate_abstract"],
    stage_args = {
        "synth": {
            "SDC_FILE": "$(location :test/constraints-top.sdc)",
            "SYNTH_HIERARCHICAL": "1",
        },
        "floorplan": {
            "CORE_UTILIZATION": "3",
            "RTLMP_FLOW": "True",
            "CORE_MARGIN": "2",
            "MACRO_PLACE_HALO": "30 30",
        },
        "place": {
            "PLACE_DENSITY": "0.20",
            "PLACE_PINS_ARGS": "-annealing",
        },
    },
    stage_sources = {
        "synth": [":test/constraints-top.sdc"],
    },
    verilog_files = ["test/rtl/L1MetadataArray.sv"],
)

The macro from the example above spawns the following Bazel targets:

Dependency targets:
  //:L1MetadataArray_cts_deps
  //:L1MetadataArray_floorplan_deps
  //:L1MetadataArray_generate_abstract_deps
  //:L1MetadataArray_grt_deps
  //:L1MetadataArray_place_deps
  //:L1MetadataArray_route_deps
  //:L1MetadataArray_synth_deps

Stage targets:
  //:L1MetadataArray_cts
  //:L1MetadataArray_floorplan
  //:L1MetadataArray_generate_abstract
  //:L1MetadataArray_grt
  //:L1MetadataArray_place
  //:L1MetadataArray_route
  //:L1MetadataArray_synth

The example comes from the BUILD file in this repository.

To test different variants of the same design, the orfs_flow can be provided with an optional argument variant.

orfs_flow(
    name = "L1MetadataArray",
    abstract_stage = "route",
    macros = ["tag_array_64x184_generate_abstract"],
    # [...]
    variant = "test",
)

This definition creates similar Bazel targets with additional variant appended after the design name:

Dependency targets:
  //:L1MetadataArray_test_cts_deps
  //:L1MetadataArray_test_floorplan_deps
  ...
  //:L1MetadataArray_test_generate_abstract_deps

Stage targets:
  //:L1MetadataArray_test_synth
  //:L1MetadataArray_test_floorplan
  ...
  //:L1MetadataArray_test_generate_abstract

Implementation

openroad.bzl

This file contains simple helper functions written in Starlark as well as macro orfs_flow(). The implementation of this macro spawns multiple genrule native rules which are responsible for preparing and running ORFS physical design flow targets during Bazel build stage.

These are the genrules spawned in this macro:

• ORFS stage-specific (named: target_name + “_” + stage or target_name + “_” + variant + “_” + stage)
• ORFS stage dependencies (named: target_name + “_” + stage + “_deps” or target_name + “_” + variant + “_” + stage + “_deps”)

Bazel flow

Regular Bazel flow uses artifacts from the Docker environment with preinstalled ORFS.

It implicitly depends on a Docker image with ORFS environment pre-installed being present. The Docker image used in the flow is defined in the module file, the default can be overridden by specifying image and sha256 attributes:

orfs = use_extension("@bazel-orfs//:extension.bzl", "orfs_repositories")
orfs.default(
    image = <image>,
    sha256 = <sha256>,
)
use_repo(orfs, "docker_orfs")

Setting this attribute to a valid image and checksum will enable Bazel to automatically pull the image and extract ORFS artifacts on bazel run or bazel build:

bazel build <target>_<stage>

NOTE: If sha256 is set to an empty string "", Bazel will attempt to use a local image with name provided in the image field.

Local flow

A locally built and modified ORFS can also be used to run the flow:

bazel run <target>_<stage>_deps -- <absolute_path> && <absolute_path>/make do-<stage>

NOTE: If the directory under the <absolute_path> does not exist, it will be created. If a relative path is provided, the bazel run command above will fail.

A convenient way to re-run the floorplan and view the results would be:

bazel run MyDesign_floorplan -- `pwd`/build && build/make do-floorplan gui_floorplan

By default, the make do-<stage> invocation will rely on the ORFS from MODULE.bazel, unless the env.sh script is sourced, or the FLOW_HOME environment variable is set to the path of the local OpenROAD-flow-scripts/flow installation:

source <orfs_path>/env.sh

bazel run <target>_<stage>_deps -- <absolute_path>
<absolute_path>/make do-<stage>

NOTE: The synthesis stage requires the do-yosys-canonicalize, do-yosys-keep-hierarchy and do-yosys steps to be completed beforehand. These steps are necessary to generate the required .rtlil file for the synthesis stage.

source <orfs_path>/env.sh

bazel run <target>_synth_deps -- <absolute_path>
<absolute_path>/make do-yosys-canonicalize do-yosys-keep-hierarchy do-yosys do-synth

Stage targets

Each stage of the physical design flow is represented by a separate target and follows the naming convention: target_name + “_” + stage.

The stages are as follows:

• synth (synthesis)
• floorplan
• place
• cts (clock tree synthesis)
• grt (global route)
• route
• final
• generate_abstract

Generate abstract targets

Those targets are used to create abstracts (.lef and .lib files) for macros.

Abstracts are generated at the target + "generate_abstract" stage, which follows one defined via abstract_stage attribute passed to the orfs_flow() macro:

orfs_flow(
    name = "tag_array_64x184",
    abstract_stage = "floorplan",
    stage_args = {
        "synth": SRAM_SYNTH_ARGUMENTS,
        "floorplan": SRAM_FLOOR_PLACE_ARGUMENTS | {
            "CORE_UTILIZATION": "40",
            "CORE_ASPECT_RATIO": "2",
        },
        "place": SRAM_FLOOR_PLACE_ARGUMENTS | {
            "PLACE_DENSITY": "0.65",
        },
    },
    stage_sources = {
        "synth": [":constraints-sram"],
        "floorplan": [":io-sram"],
        "place": [":io-sram"],
    },
    verilog_files = ["//another:tag_array_64x184.sv"],
    visibility = [":__subpackages__"],
)

By default it's the latest ORFS-specific target (final).

NOTE: Abstracts can be generated starting from the floorplan stage, thus skipping the synth stage.

Abstracts are intended to be used in builds of other parts of the design that use the given macro. They're useful for estimating sizes of macros with long build times and checking if they will fit in upper-level modules without running time consuming place and route flow.

NOTE: Stages that follow the one passed to abstract_stage will not be created by the orfs_flow() macro.

Mock area targets

Mock area targets are created on top of the stage targets and overrides _generate_abstract target to produced mocked abstracts.

The flow contains:

• target_name_variant + “_synth_mock_area” - synthesis which has its whole internal logic removed,
• target_name_variant + “_mock_area” - reads DIE_AREA and CORE_AREA from default floorplan results and scale them by value defined in mock_area,
• target_name_variant + “_floorplan_mock_area” - floorplan with overridden DIE_AREA and CORE_AREA values,
• target_name_variant + “_generate_abstract” - abstracts generated based on mocked synthesis and floorplan.

To create mock area targets, mock_area has to be added to orfs_flow definition:

orfs_flow(
    name = "lb_32x128",
    stage_args = LB_STAGE_ARGS,
    stage_sources = LB_STAGE_SOURCES,
    verilog_files = LB_VERILOG_FILES,
    mock_area = 0.5,
)

The mock has the same pinout as the original macro and similar size which makes it useful in early design stages.

Constraints handling

Constraint files are passed down to orfs_flow() macro through Stage targets arguments and sources:

orfs_flow(
    name = "tag_array_64x184",
    abstract_stage = "synth",
    stage_args = {
        "synth": {
            "SDC_FILE": "$(location :constraints-sram)",
        },
    },
    stage_sources = {
        "synth": [":constraints-sram"],
    },
    verilog_files = ["//another:tag_array_64x184.sv"],
    visibility = [":__subpackages__"],
)

Those accept a Bazel label that points to the file. There are however cases, where e.g. SRAM constraints file includes additional TCL script. In such scenario a filegroup should also define the data attribute with the additional script.

filegroup(
    name = "constraints-sram",
    srcs = [
        ":test/constraints-sram.sdc",
    ],
    data = [
        ":test/util.tcl",
    ],
    visibility = [":__subpackages__"],
)

Dependency targets

The dependency targets fall under the target_name + “_” + variant + “_” +stage + “_deps” naming convention, and are used to prepare the environment for running the ORFS stage targets. Each stage of the physical design flow depend on two generated .mk files that provide the configuration for the ORFS. One is specific for the stage of the flow and the second one is common for the whole design being built.

They can be found under the following paths:

<path>/config.mk                                                             # Common for the whole design
<path>/results/<module>/<target>/<variant>/<stage_number>_<stage>.short.mk   # Specific for the stage

Additionally, the dependency targets are responsible for constraints handling and generating the shell scripts that are used to run the ORFS stages both in the Bazel and Local flow:

<path>/make     # Running the ORFS stages
<path>/results  # Directory for the results of the flow
<path>/external # Directory for the external dependencies

GUI targets

The GUI and CLI targets can only be run from the generated shell script.

For the GUI:

bazel run <target>_<stage> -- <absolute_path>
<absolute_path>/make gui_<stage>

For the CLI:

bazel run <target>_<stage> -- <absolute_path>
<absolute_path>/make open_<stage>

CLI and GUI is not available for all stages, consequently these targets are created only for:

• floorplan
• place
• cts (clock tree synthesis)
• grt (global route)
• route
• final

Tutorial

To execute the build flow for the cts (Clock Tree Synthesis) stage of the L1MetadataArray target, use the following command:

bazel run @bazel-orfs//:L1MetadataArray_cts -- `pwd`/build

Bazel will automatically download the Docker image with the ORFS environment and run the flow.

This will build the L1MetadataArray target up to the cts stage and place the results in the build/results directory. It's important to provide an absolute path to the directory where the flow artifacts will be stored.

Dependencies in ORFS Makefile versus Bazel

When using bazel-orfs, the dependency checking is done by Bazel instead of ORFS's makefile, with the exception of the synthesis canonicalization stage.

ORFS make do-yosys-canonicalize is special and will do dependency checking using ORFS Makefile and output $(RESULTS_DIR)/1_synth.rtlil.

The .rtlil is Yosys's internal representation format of all the various input files that went into Yosys, however any unused modules have been deleted and the modules are in canonical form(ordering of the Verilog files provided to Yosys won't matter). However, .rtlil still contains line number information for debugging purposes. The canonicalization stage is quick compared to synthesis and adds no measurable overhead.

Canonicalization simplifies specifying VERILOG_FILES to ORFS in Bazel, simply glob them all and let Yosys figure out which files are actually used. This avoids redoing synthesis unnecessarily if, for instance, a Verilog file related to simulation changes.

The next stage is make do-yosys which does no dependency checking, leaving it to Bazel. do-yosys completes the synthesis using $(RESULTS_DIR)/1_synth.rtlil.

The subsequent ORFS stages are run with make do-floorplan do-place ... and these stages do no dependency checking, leaving it to Bazel.

bazel-orfs also does dependency checking of options provided to each stage. If a property to CTS is changed, then no steps ahead of CTS is re-run. bazel-orfs does not know which properties belong to which stage, it is the responsibility of the user to pass properties to the correct stage. This includes some slightly surprising responsibilities, such as passing IO pin constraints to both floorplan and placement.

Using the local flow

The local flow allows testing the build with locally built OpenROAD-flow-scripts. It is based on Bazel make targets, for more information on those, please refer to Dependency targets paragraph.

Let's assume we want to perform a floorplan stage for the L1MetadataArray design using the locally built ORFS.

1. Source env.sh of your local ORFS installation or set the FLOW_HOME environment variable to the path to your local OpenROAD-flow-scripts/flow directory:

source <ORFS_path>/env.sh
# Or
export FLOW_HOME=<ORFS_path>/flow

2. Build the stages prior to the floorplan stage:

# Initialize dependencies for the Synthesis stage for L1MetadataArray target
bazel run @bazel-orfs//:L1MetadataArray_synth_deps -- `pwd`/build

# Build Synthesis stage for L1MetadataArray target using local ORFS
build/make do-yosys-canonicalize do-yosys-keep-hierarchy do-yosys do-synth

# Initialize dependencies for the Floorplan stage for L1MetadataArray target
bazel run @bazel-orfs//:L1MetadataArray_floorplan_deps -- `pwd`/build

3. Execute the shell script with ORFS make target relevant to given stage of the flow:

build/make do-floorplan

Running OpenROAD GUI

Let's assume we want to run a GUI for the route stage for the L1MetadataArray target.

1. Initialize and build stages up to the route stage:

bazel run @bazel-orfs//:L1MetadataArray_route -- `pwd`/build

2. Execute the GUI shell script:

# Start the GUI for the Route stage for L1MetadataArray target
build/make gui_route

# Or open the GUI through the CLI
build/make open_route
gui::show

Tweaking aspect ratio of a floorplan

Notice how the CORE_ASPECT_RATIO parameter is associated with the floorplan and only the floorplan stage below:

diff --git a/BUILD b/BUILD
index 095d63b..4b78dea 100644
--- a/BUILD
+++ b/BUILD
@@ -74,7 +74,7 @@ orfs_flow(
         "synth": SRAM_SYNTH_ARGUMENTS,
         "floorplan": SRAM_FLOOR_PLACE_ARGUMENTS | {
             "CORE_UTILIZATION": "40",
-            "CORE_ASPECT_RATIO": "2",
+            "CORE_ASPECT_RATIO": "4",
         },
         "place": SRAM_FLOOR_PLACE_ARGUMENTS | {
             "PLACE_DENSITY": "0.65",

Bazel will detect this change specifically as a change to the floorplan, re-use the synthesis result and rebuild from the floorplan stage. Similarly, if the PLACE_DENSITY is modified, only stages from the placement and on are re-built.

To apply and view the changes:

# Build tag_array_64x184 macro up to the floorplan stage
bazel run @bazel-orfs//:tag_array_64x184_floorplan -- `pwd`/build

# View final results from GUI
build/make gui_floorplan

If the remote caching is enabled for Bazel, reverting the change and rebuilding the floorplan stage will be completed instantaneously, as the artifact already exists:

# Revert the change
git restore BUILD

# Rebuild the floorplan stage
bazel run @bazel-orfs//:tag_array_64x184_floorplan -- `pwd`/build

# View final results from GUI
build/make gui_floorplan

Fast floorplanning and mock abstracts

Let's say we want to skip place, cts and route and create a mock abstract where we can at least check that there is enough place for the macros at the top level.

WARNING: Although mock abstracts can speed up turnaround times, skipping place, cts or route can lead to errors and problems that don't exist when place, cts and route are not skipped.

To do so, we modify in BUILD file the abstract_stage attribute of orfs_flow macro to floorplan stage:

diff --git a/BUILD b/BUILD
index 095d63b..9756fbf 100644
--- a/BUILD
+++ b/BUILD
@@ -110,7 +110,7 @@ orfs_flow(

 orfs_flow(
     name = "L1MetadataArray",
-    abstract_stage = "route",
+    abstract_stage = "floorplan",
     macros = ["tag_array_64x184_generate_abstract"],
     stage_args = {
         "synth": {

This will generate targets that can be verified in the bazel query output:

bazel query '...:*' | grep 'L1MetadataArray'

//:L1MetadataArray_synth_deps
//:L1MetadataArray_synth
//:L1MetadataArray_floorplan_deps
//:L1MetadataArray_floorplan
//:L1MetadataArray_generate_abstract

The abstract stage follows the one defined via abstract_stage attribute passed to the orfs_flow() macro. However it always falls down to the <target>_generate_abstract pattern and can be built with the following command:

bazel build @bazel-orfs//:L1MetadataArray_generate_abstract

This will cause the Bazel to generate the abstracts for the design right after the floorplan stage instead of route stage. The output LEF file can be found under the bazel-bin/results/<module>/<target>/base/<target.lef> path.

For more information please refer to the description of Abstract targets.

Bazel hacking

Run all synth targets

bazel query :\* | grep '_synth$' | xargs -I {} bazel run {} -- `pwd`/build

This will run all synth targets in the workspace and place the results in the build/results directory.

Forcing a rebuild of a stage

Sometimes it is desirable, such as when hacking ORFS, to redo a build stage even if none of the dependencies for that stage changed. This can be achieved by changing a PHONY variable to that stage and bumping it:

diff --git a/BUILD b/BUILD
index 095d63b..5b618ba 100644
--- a/BUILD
+++ b/BUILD
@@ -114,6 +114,7 @@ orfs_flow(
     name = "L1MetadataArray",
     abstract_stage = "route",
     macros = ["tag_array_64x184_generate_abstract"],
     stage_args = {
         "synth": {
+            "PHONY": "1",
             "SDC_FILE": "$(location :test/constraints-top.sdc)",
             "SYNTH_HIERARCHICAL": "1",
         },

Building the immediate dependencies of a target

bazel build @bazel-orfs//:L1MetadataArray_synth_deps

This will build the immediate dependencies of the L1MetadataArray target up to the synth stage and place the results in the bazel-bin directory. Later, those dependencies will be used by Bazel to build the synth stage for L1MetadataArray target.

Tools location after bazel run ...

A mutable build folder can be set up to prepare for a local synthesis run, useful when digging into some detail of synthesis flow:

$ bazel build tag_array_64x184_synth_deps -- `pwd`/build
$ build/make print-YOSYS_EXE
YOSYS_EXE = external/_main~orfs_repositories~docker_orfs/OpenROAD-flow-scripts/tools/install/yosys/bin/yosys

This is actually a symlink pointing to the read only executables, which is how yosys is able to find the yosys-abc alongside itself needed for the abc part of the synthesis stage:

$ ls -l $(dirname $(readlink -f build/external/_main~orfs_repositories~docker_orfs/OpenROAD-flow-scripts/tools/install/yosys/bin/yosys))
total 37456
-rwxr-xr-x 1 oyvind oyvind 23449673 Aug 15 07:05 yosys
-rwxr-xr-x 1 oyvind oyvind 14725193 Aug 15 07:05 yosys-abc
-rwxr-xr-x 1 oyvind oyvind     3904 Aug  7 23:11 yosys-config
-rwxr-xr-x 1 oyvind oyvind    65609 Aug 15 07:05 yosys-filterlib
-rwxr-xr-x 1 oyvind oyvind    73845 Aug  7 23:11 yosys-smtbmc
-rwxr-xr-x 1 oyvind oyvind    17377 Aug  7 23:11 yosys-witness

make issue floorplan example

To create and test a make issue archive for floorplan:

bazel run lb_32x128_floorplan_deps `pwd`/build
build/make ISSUE_TAG=test floorplan_issue

This results in build/floorplan_test.tar.gz, which can be run provided there openroad application is in the path.

A local ORFS installation can be used by running source env.sh.

Alternatively, the ORFS installation used with Bazel, can be used by using make bash to set up the environment of the ORFS extracted into the Bazel build environment:

build/make bash
export PATH=$PATH:$(realpath $(dirname $(readlink -f $OPENROAD_EXE)))
tar --strip-components=1 -xzf ../floorplan_test.tar.gz
./run-me-lb_32x128-asap7-base.sh