5.9. Advanced Usage

5.9.1. Alternative RTL Flows

The Make-based build system provided supports using Hammer without using RTL generated by Chipyard. To push a custom Verilog module through, one only needs to append the following environment variables to the make buildfile command (or edit them directly in the Makefile).

CUSTOM_VLOG=<your Verilog files>
VLSI_TOP=<your top module>

CUSTOM_VLOG breaks the dependency on the rest of the Chipyard infrastructure and does not start any Chisel/FIRRTL elaboration. VLSI_TOP selects the top module from your custom Verilog files.

5.9.2. Under the Hood

To uncover what is happening under the hood, here are the commands that are executed:

For make syn:

./example-vlsi -e /path/to/env.yml -p /path/to/example.yml -p /path/to/inputs.yml --obj_dir /path/to/build syn

example-vlsi is the entry script as explained before, -e provides the environment yml, -p points to configuration yml/jsons, --obj_dir speficies the destination directory, and syn is the action.

For make par:

./example-vlsi -e /path/to/env.yml -p /path/to/syn-output-full.json -o /path/to/par-input.json --obj_dir /path/to/build syn-to-par
./example-vlsi -e /path/to/env.yml -p /path/to/par-input.json --obj_dir /path/to/build par

A syn-to-par action translates the synthesis output configuration into an input configuration given by -o. Then, this is passed to the par action.

For more information about all the options that can be passed to the Hammer command-line driver, please see the Hammer documentation.

5.9.3. Manual Step Execution & Dependency Tracking

It is invariably necessary to debug certain steps of the flow, e.g. if the power strap settings need to be updated. The underlying Hammer commands support options such as --to_step, --from_step, and --only_step. These allow you to control which steps of a particular action are executed.

Make’s dependency tracking can sometimes result in re-starting the entire flow when the user only wants to re-run a certain action. Hammer’s build system has “redo” targets such as redo-syn and redo-par to run certain actions without typing out the entire Hammer command.

Say you need to update some power straps settings in example.yml and want to try out the new settings:

make redo-par HAMMER_REDO_ARGS='-p example.yml --only_step power_straps'

5.9.4. Hierarchical RTL/Gate-level Simulation, Power Estimation

With the Synopsys plugin, hierarchical RTL and gate-level simulation is supported using VCS at the chip-level. Also, post-par power estimation with Voltus in the Cadence plugin is also supported. Special Make targets are provided in the vlsi/ directory in sims.mk and power.mk. Here is a brief description:

  • sim-rtl: RTL-level simulation

    • sim-rtl-debug: Also write a VPD waveform

  • sim-syn: Post-synthesis gate-level simulation

    • sim-syn-debug: Also write a VPD waveform

    • sim-syn-timing-debug: Timing-annotated with VPD waveform

  • sim-par: Post-par gate-level simulation

    • sim-par-debug: Also write a VPD waveform

    • sim-par-timing-debug: Timing-annotated with VPD waveform

  • power-par: Post-par power estimation

    • Note: this will run sim-par first

  • redo- can be appended to all above targets to break dependency tracking, like described above.

  • -$(VLSI_TOP) suffixes denote simulations/power analysis on a submodule in a hierarchical flow. Note that you must provide the testbenches for these modules since the default testbench only simulates a Chipyard-based ChipTop DUT instance.

The simulation configuration (e.g. binaries) can be edited for your design. See the Makefile and refer to Hammer’s documentation for how to set up simulation parameters for your design.