5.8. Sky130 Commercial 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 requires access to the included Mentor tool plugin submodule, which is needed for DRC & LVS.
5.8.1. 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.
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 ASAP7 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.
Genus, Innovus, Voltus, VCS, and Calibre licenses
These SRAM macros were generated using the Sram22 SRAM generator (still very heavily under development)
126.96.36.199. Quick Prerequisite Setup
As of recently, the Sky130A PDK may be installed via conda. The prerequisite setup for this tutorial may eventually be scripted, but for now the directions to set them up are below.
# 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
5.8.3. Initial Setup
In the Chipyard root, ensure that you have the Chipyard conda environment activated. Then, run:
to pull and install the plugin submodules. Note that for technologies other than
asap7, the tech submodule must be added in the
vlsi folder first.
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 a commercial tool flow. It selects tools for synthesis (Cadence Genus), place and route (Cadence Innovus), DRC and LVS (Mentor Calibre).
5.8.4. 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-commercial
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 present for the OpenROAD flow), 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 purpose 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-commercialgives 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.
5.8.5. Running the VLSI Flow
make syn tutorial=sky130-commercial
Post-synthesis logs and collateral are in
build/syn-rundir. The raw quality of results data is available at
build/syn-rundir/reports, and methods to extract this information for design space exploration are a work in progress.
make par tutorial=sky130-commercial
After completion, the final database can be opened in an interactive Innovus session via
Intermediate database are written in
build/par-rundir between each step of the
par action, and can be restored in an interactive Innovus session as desired for debugging purposes.
Timing reports are found in
build/par-rundir/timingReports. They are gzipped text files.
188.8.131.52. DRC & LVS
To run DRC & LVS, and view the results in Calibre:
make drc tutorial=sky130-commercial
make lvs tutorial=sky130-commercial
Some DRC errors are expected from this PDK, especially with regards to the SRAMs, as explained in the
Sky130 Hammer plugin README.
For this reason, the
example-vlsi-sky130 script black-boxes the SRAMs for DRC/LVS analysis.
Simulation with VCS is supported, and can be run at the RTL- or gate-level (post-synthesis and post-P&R). The simulation infrastructure as included here is intended for running RISC-V binaries on a Chipyard config. For example, for an RTL-level simulation:
make sim-rtl tutorial=sky130-commercial BINARY=$RISCV/riscv64-unknown-elf/share/riscv-tests/isa/rv64ui-p-simple
Post-synthesis and post-P&R simulations use the
sim-par make targets, respectively.
-debug-timing to these make targets will instruct VCS to write a SAIF + FSDB (or VPD if the
USE_VPD flag is set) and do timing-annotated simulations, respectively. See the
sim.mk file for all available targets.
184.108.40.206. Power/Rail Analysis
Post-P&R power and rail (IR drop) analysis is supported with Voltus:
make power-par tutorial=sky130-commercial
If you append the
BINARY variable to the command, it will use the activity file generated from a
sim-<syn/par>-debug run and report dynamic power & IR drop from the toggles encoded in the waveform.
To bypass gate-level simulation, you will need to run the power tool manually (see the generated commands in the generated
hammer.d buildfile). Static and active (vectorless) power & IR drop will be reported.
220.127.116.11. 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 statements 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"