Dromajo Co-simulation with BOOM designs

Instead of using TracerV to provide a cycle-by-cycle trace of a target CPU’s architectural state, you can use the Dromajo co-simulator to verify the functionality of a BOOM design.


This work is highly experimental. We hope to integrate this into FireSim in a cleaner fashion at a later point.


This work currently only works for single core BOOM designs.

Building a Design with Dromajo

In all FireChip designs, TracerV is included by default. To enable Dromajo, you just need to add the Dromajo bridge (WithDromajoBridge) to your BOOM target design config (default configs. located in $CHIPYARD/generators/firechip/src/main/scala/TargetConfigs.scala). An example configuration with Dromajo is shown below:

class FireSimLargeBoomConfig extends Config(
  new WithDromajoBridge ++ // add Dromajo bridge to simulation
  new WithDefaultFireSimBridges ++
  new WithDefaultMemModel ++
  new WithFireSimConfigTweaks ++
  new chipyard.LargeBoomConfig)

At this point, you should run the firesim buildafi command for the BOOM config wanted.

Running a FireSim Simulation

To run a simulation with Dromajo, you must modify the workload json to support Dromajo. The following is an example using the base Linux workload generated from FireMarshal and modifying it for Dromajo. Here is the modified workload json (renamed to br-base-dromajo from br-base):

  "benchmark_name": "br-base-dromajo",
  "common_simulation_outputs": [
  "common_bootbinary": "../../../../../software/firemarshal/images/br-base-bin",
  "common_rootfs": "../../../../../software/firemarshal/images/br-base.img",
  "common_simulation_inputs": [

You will notice there are two extra simulation inputs needed compared to the “base” unmodified br-base workload: a bootrom (rom) and a device tree blob (dtb). Both files are found in your generated sources and should be moved into the workload directory (i.e. workloads/br-base-dromajo).


# copy/rename the rom file and put in the proper folder
cp sim/generated-src/f1/<LONG_NAME>/<LONG_NAME>.rom $FIRESIM/deploy/workloads/br-base-dromajo/br-base-bin.rom

# copy/rename the dtb file and put in the proper folder
cp sim/generated-src/f1/<LONG_NAME>/<LONG_NAME>.dtb $FIRESIM/deploy/workloads/br-base-dromajo/br-base-bin.dtb

After this process, you should see the following workloads/br-base-dromajo folder layout:



The name of the rom and dtb files must match the name of the workload binary i.e. common_bootbinary.

At this point you are ready to run the simulation with Dromajo. The commit log trace will by default print to the uartlog. However, you can avoid printing it out by changing verbose == false in the dromajo_cosim.cpp file located in $CHIPYARD/tools/dromajo/dromajo-src/src/ folder.

Troubleshooting Dromajo Simulations with MIDAS Simulations

If FPGA simulation fails with Dromajo, you can use MIDAS-level simulation to determine if your Dromajo setup is correct. First refer to Debugging & Testing with RTL Simulation for more information on MIDAS-level simulation. The main difference between those instructions and simulations with Dromajo is that you need to manually point to the dtb, rom, and binary files when invoking the simulator. Here is an example of a make command that can be run to check for a correct setup.

# enter simulation directory
cd $FIRESIM/sim/

# make command to run a binary
# <BIN> - absolute path to binary
# <DTB> - absolute path to dtb file
# <BOOTROM> - absolute path to rom file
# <YourBoomConfig> - Single-core BOOM configuration to test
make TARGET_CONFIG=<YourBoomConfig> SIM_BINARY=<BIN> EXTRA_SIM_ARGS="+drj_dtb=<DTB> +drj_rom=<BOOTROM> +drj_bin=<BIN>" run-vcs

It is important to have the +drj_* arguments, otherwise Dromajo will not match the simulation running on the DUT.


Sometimes simulations in VCS will diverge unless a +define+RANDOM=0 is added to the VCS flags in sim/midas/src/main/cc/rtlsim/Makefrag-vcs.


Dromajo currently only works in VCS and FireSim simulations.