5.2. Core Hammer
Hammer is a physical design flow which encourages reusability by partitioning physical design specifications into three distinct concerns: design, CAD tool, and process technology. Hammer wraps around vendor specific technologies and tools to provide a single API to address ASIC design concerns. Hammer allows for reusability in ASIC design while still providing the designers leeway to make their own modifications.
Hammer implements a VLSI flow using the following high-level constructs:
Actions are the top-level tasks Hammer is capable of executing (e.g. synthesis, place-and-route, etc.)
Steps are the sub-components of actions that individually addressable in Hammer (e.g. placement in the place-and-route action).
Hooks are modifications to steps or actions that are programmatically defined in a Hammer configuration.
5.2.4. VLSI Flow Control
Sometimes we want more fine-grained control of the VLSI flow than at the action level.
The Hammer flow supports being able to start/stop before/after any of the steps in a particular action.
See the Hammer documentation on Flow Control for a full list and description of the options.
Makefile in the
vlsi directory passes this extra information via the
This variable can also be used to specify additional YAML configurations that may have
changed or been omitted from the inital build.
5.3. Configuration (Hammer IR)
To configure a Hammer flow, supply a set
json configuration files that chooses the tool and technology plugins and versions as well as any design specific configuration options. Collectively, this configuration API is referred to as Hammer IR and can be generated from higher-level abstractions.
The current set of all available Hammer APIs is codified here.
5.4. Tool Plugins
Hammer supports separately managed plugins for different CAD tool vendors. You may be able to acquire access to the included Cadence, Synopsys, and Mentor plugins repositories with permission from the respective CAD tool vendor. The types of tools (by Hammer names) supported currently include:
Several configuration variables are needed to configure your tool plugin of choice.
First, select which tool to use for each action by setting
vlsi.core.<tool_type>_tool to the name of your tool, e.g.
Then, point Hammer to the folder that contains your tool plugin by setting
This directory should include a folder with the name of the tool, which itself includes a python file
__init__.py and a yaml file
defaults.yml. Customize the version of the tool by setting
<tool_type>.<tool_name>.version to a tool specific string.
__init__.py file should contain a variable,
tool, that points to the class implementing this tool.
This class should be a subclass of
Hammer<tool_type>Tool, which will be a subclass of
HammerTool. The class should implement methods for all the tool’s steps.
defaults.yml file contains tool-specific configuration variables. The defaults may be overridden as necessary.
5.5. Technology Plugins
Hammer supports separately managed technology plugins to satisfy NDAs. You may be able to acquire access to certain pre-built technology plugins with permission from the technology vendor. Or, to build your own tech plugin, you need at least a
__init__.py is optional if there are any technology-specific methods or hooks to run.
The ASAP7 plugin is a good starting point for setting up a technology plugin because it is an open-source example that is not suitable for taping out a chip. Refer to Hammer’s documentation for the schema and detailed setup instructions.
Several configuration variables are needed to configure your technology of choice.
First, choose the technology, e.g.
vlsi.core.technology: asap7, then point to the location with the PDK tarball with
technology.<tech_name>.tarball_dir or pre-installed directory with
technology.<tech_name>.install_dir and (if applicable) the plugin repository with
Technology-specific options such as supplies, MMMC corners, etc. are defined in their respective
vlsi.inputs... configurations. Options for the most common use case are already defined in the technology’s
defaults.yml and can be overridden by the user.