5.5. Hammer Buildfile

Hammer natively supports a GNU Make-based build system to manage build dependencies. To use this flow, vlsi.core.build_system must be set to make. Hammer will generate a Makefile include in the object directory named hammer.d after calling the build action:

hammer-vlsi -e env.yml -p config.yml --obj_dir build build

hammer.d will contain environment variables needed by Hammer and a target for each major Hammer action (e.g. par, synthesis, etc. but not syn-to-par, which is run automatically when calling make par). For a flat design, the dependencies are created betwen the major Hammer actions. For hierarchical designs, Hammer will use the hierarchy to build a dependency graph and construct the Make target dependencies appropriately. hammer.d should be included in a higher-level Makefile. While hammer.d defines all of the variables that it needs, there are often reasons to set these elsewhere. Because hammer.d uses ?= assignment, the settings created in the top-level Makefile will persist. An example of this setup is found in Chipyard.

To enable interactive usage, Hammer will also create a set of “redo” targets (e.g. redo-par and redo-syn). These targets intentionally have no dependency information; they are for advanced users to make changes to the input config and/or edit the design manually, then continue the flow. Additional arguments can be passed to the “redo” targets with the HAMMER_EXTRA_ARGS environment variable. This allows the user to create “patches” to the configuration, which can be easily passed to Hammer by setting, for example, HAMMER_EXTRA_ARGS="-p patch.yml". Other potential uses for HAMMER_EXTRA_ARGS include using --to_step/--until_step and --from_step/after_step to stop a run at a particular step or resume one from a previous iteration.