5.9. Sky130 + OpenROAD Tutorial
vlsi folder of this repository contains an example Hammer flow with the TinyRocketConfig from Chipyard. This example tutorial uses the built-in Sky130 technology plugin and OpenROAD tool plugin.
5.9.1. Project Structure
This example gives a suggested file structure and build system. The
vlsi/ folder will eventually contain the following files and folders:
Integration of Hammer’s build system into Chipyard and abstracts away some Hammer commands.
Hammer output directory. Can be changed with the
Will contain subdirectories such as
inputs.ymldenoting the top module and input Verilog files.
This file is not used in this tutorial, but is required for the commercial tool flow. A template file for tool environment configuration. Fill in the install and license server paths for your environment. For SLICE and BWRC affiliates, example environment configs are found here.
Entry point to Hammer. Contains example placeholders for hooks.
Hammer IR for this tutorial. For SLICE and BWRC affiliates, an example Sky130 config is found here.
Hammer IR not used for this tutorial but provided as templates.
All of the elaborated Chisel and FIRRTL.
Tool plugin repositories not used for this tutorial (they are provided in the hammer-vlsi package).
OpenROAD flow tools:
These SRAM macros were generated using the Sram22 SRAM generator (still very heavily under development)
220.127.116.11. Quick Prerequisite Setup
As of recently, most of the prerequisites of this tutorial may now be installed as conda packages. The prerequisite setup for this tutorial may eventually be scripted, but for now the directions to set them up are below. Note that we create a new conda environment for each tool because some of them have conflicting dependencies.
# download all files for Sky130A PDK
conda create -c litex-hub --prefix ~/.conda-sky130 open_pdks.sky130a=1.0.399_0_g63dbde9
# clone the SRAM22 Sky130 SRAM macros
git clone https://github.com/rahulk29/sram22_sky130_macros ~/sram22_sky130_macros
# install all VLSI tools
conda create -c litex-hub --prefix ~/.conda-yosys yosys=0.27_4_gb58664d44
conda create -c litex-hub --prefix ~/.conda-openroad openroad=2.0_7070_g0264023b6
conda create -c litex-hub --prefix ~/.conda-klayout klayout=0.28.5_98_g87e2def28
conda create -c litex-hub --prefix ~/.conda-signoff magic=8.3.376_0_g5e5879c netgen=1.5.250_0_g178b172
5.9.3. Initial Setup
In the Chipyard root, ensure that you have the Chipyard conda environment activated. Then, run:
./scripts/init-vlsi.sh sky130 openroad
to pull and install the plugin submodules. Note that for technologies other than
asap7, the tech submodule is cloned in the
and for the commercial tool flow (set up by omitting the
openroad argument), the tool plugin submodules are cloned into the
Now navigate to the
vlsi directory. The remainder of the tutorial will assume you are in this directory.
We will summarize a few files in this directory that will be important for the rest of the tutorial.
This is the entry script with placeholders for hooks. In the
ExampleDriver class, a list of hooks is passed in the
get_extra_par_hooks. Hooks are additional snippets of python and TCL (via
x.append()) to extend the Hammer APIs. Hooks can be inserted using the
make_pre/post/replacement_hook methods as shown in this example. Refer to the Hammer documentation on hooks for a detailed description of how these are injected into the VLSI flow.
This contains the Hammer configuration for this example project. Example clock constraints, power straps definitions, placement constraints, and pin constraints are given. Additional configuration for the extra libraries and tools are at the bottom.
Add the following YAML keys to the top of this file to specify the location of the Sky130A PDK and SRAM macros.
# all ~ should be replaced with absolute paths to these directories
# technology paths
This contains the Hammer configuration for the OpenROAD tool flow. It selects tools for synthesis (Yosys), place and route (OpenROAD), DRC (Magic), and LVS (NetGen).
Add the following YAML keys to the top of this file to specify the locations of the tool binaries. Note that this is not required if the tools are already on your PATH.
# all ~ should be replaced with absolute paths to these directories
# tool binary paths
5.9.4. Building the Design
To elaborate the
TinyRocketConfig and set up all prerequisites for the build system to push the design and SRAM macros through the flow:
make buildfile tutorial=sky130-openroad
make buildfile generates a set of Make targets in
It needs to be re-run if environment variables are changed.
It is recommended that you edit these variables directly in the Makefile rather than exporting them to your shell environment.
buildfile make target has dependencies on both (1) the Verilog that is elaborated from all Chisel sources
and (2) the mapping of memory instances in the design to SRAM macros;
all files related to these two steps reside in the
Note that the files in
generated-src vary for each tool/technology flow.
This especially applies to the Sky130 Commercial vs OpenROAD tutorial flows
(due to the
ENABLE_YOSYS_FLOW flag, explained below), so these flows should be run in separate
chipyard installations. If the wrong sources are generated, simply run
make buildfile -B to rebuild all targets correctly.
For the sake of brevity, in this tutorial we will set the Make variable
which will cause additional variables to be set in
tutorial.mk, a few of which are summarized as follows:
CONFIG=TinyRocketConfigselects the target generator config in the same manner as the rest of the Chipyard framework. This elaborates a stripped-down Rocket Chip in the interest of minimizing tool runtime.
tech_name=sky130sets a few more necessary paths in the
Makefile, such as the appropriate Hammer plugin
TECH_CONFselect the approproate YAML configuration files,
example-sky130.yml, which are described above
EXTRA_CONFSallow for additonal design-specific overrides of the Hammer IR in
VLSI_OBJ_DIR=build-sky130-openroadgives the build directory a unique name to allow running multiple flows in the same repo. Note that for the rest of the tutorial we will still refer to this directory in file paths as
build, again for brevity.
VLSI_TOPis by default
ChipTop, which is the name of the top-level Verilog module generated in the Chipyard SoC configs. By instead setting
VLSI_TOP=Rocket, we can use the Rocket core as the top-level module for the VLSI flow, which consists only of a single RISC-V core (and no caches, peripherals, buses, etc). This is useful to run through this tutorial quickly, and does not rely on any SRAMs.
ENABLE_YOSYS_FLOW = 1is required for synthesis through Yosys. This reverts to the Scala FIRRTL Compiler so that unsupported multidimensional arrays are not generated in the Verilog.
5.9.5. Running the VLSI Flow
make syn tutorial=sky130-openroad
Post-synthesis logs and collateral are in
make par tutorial=sky130-openroad
Note that sometimes OpenROAD freezes on commands following the
so for now we recomment running place-and-route until the
then re-starting the flow at this step. See the VLSI Flow Control documentation
below for how to break up the flow into these steps.
After completion, the final database can be opened in an interactive OpenROAD session. Hammer generates a convenient script to launch these sessions
Note that the conda OpenROAD package was compiled with the GUI disabled, so in order to view the layout, you will need to install OpenROAD from source.
Below is the post-PnR layout for the TinyRocketConfig in Sky130 generated by OpenROAD.
Intermediate databases are written in
build/par-rundir between each step of the
These databases can be restored using the same
open_chip script for debugging purposes.
Usage: ./generated-scripts/open_chip [-t] [openroad_db_name]
openroad_db_name : Name of database to load (default=latest)
-t, --timing : Load timing info (default=disabled because of slow load time)
-h, --help : Display this message
# load pre-global route database without timing information
# load post-clock tree database with timing inforamtion
./generated_scripts/open_chip -t post_clock_tree
Various reports, including timing reports, are found in
See the OpenROAD tool plugin for the full list of OpenROAD tool steps and their implementations.
18.104.22.168. DRC & LVS
As a note, this tutorial has been run extensively through commercial signoff tools, thus the open-source signoff flow is not stable or guaranteed to produce useful results. We welcome any contributions to improving both our Magic tool plugin and Netgen tool plugin.
To run DRC & LVS in Magic & Netgen, respectively:
make drc tutorial=sky130-openroad
make lvs tutorial=sky130-openroad
Note that in
sky130-openroad.yml we have set the following YAML keys:
These keys cause the Hammer plugin to only generate all necessary scripts, without executing them with the respective tool.
This is because Magic and Netgen, as of the writing of this tutorial, do not have a database format that may be loaded interactively,
so to view the DRC/LVS results for debugging you must launch the tool interactively, then run DRC/LVS checks,
which is done by the
22.214.171.124. VLSI Flow Control
Firt, refer to the VLSI Flow Control documentation. The below examples use the
redo-par Make target to re-run only place-and-route.
redo- may be prepended to any of the VLSI flow actions to re-run only that action.
# the following two commands run the entire flow, using the pre_extraction
# database to save and reload a checkpoint of the design
make par HAMMER_EXTRA_ARGS="--stop_after_step extraction"
make redo-par HAMMER_EXTRA_ARGS="--start_before_step extraction"
# the following two commands are equivalent because the extraction
# step immediately precedes the write_design step
make redo-par HAMMER_EXTRA_ARGS="--start_after_step extraction"
make redo-par HAMMER_EXTRA_ARGS="--start_before_step write_design"
# example of re-running only floorplanning to test out a new floorplan configuration
# the "-p file.yml" causes file.yml to override any previous yaml/json configurations
make redo-par \
HAMMER_EXTRA_ARGS="--only_step floorplan_design -p example-designs/sky130-openroad.yml"
For more information about Hammer’s underlying implementation, visit the Hammer documentation website.