2.2. FPGA-Accelerated Simulation

2.2.1. FireSim

FireSim is an open-source cycle-accurate FPGA-accelerated full-system hardware simulation platform that runs on cloud FPGAs (Amazon EC2 F1). FireSim allows RTL-level simulation at orders-of-magnitude faster speeds than software RTL simulators. FireSim also provides additional device models to allow full-system simulation, including memory models and network models.

FireSim currently supports running only on Amazon EC2 F1 FPGA-enabled virtual instances. In order to simulate your Chipyard design using FireSim, if you have not already, follow the initial EC2 setup instructions as detailed in the FireSim documentation. Then clone Chipyard onto your FireSim manager instance, and setup your Chipyard repository as you would normally.

Next, initalize FireSim as a library in Chipyard by running:

# At the root of your chipyard repo
./scripts/firesim-setup.sh --fast

firesim-setup.sh initializes additional submodules and then invokes firesim’s build-setup.sh script adding --library to properly initialize FireSim as a library submodule in chipyard. You may run ./sims/firesim/build-setup.sh --help to see more options.

Finally, source the following environment at the root of the firesim directory:

cd sims/firesim
# (Recommended) The default manager environment (includes env.sh)
source sourceme-f1-manager.sh


Every time you want to use FireSim with a fresh shell, you must source this sourceme-f1-manager.sh

At this point you’re ready to use FireSim with Chipyard. If you’re not already familiar with FireSim, please return to the FireSim Docs, and proceed with the rest of the tutorial.

2.2.2. Running your Design in FireSim

Converting a Chipyard config (one in chipyard/src/main/scala to run in FireSim is simple. We are using the same target (top) RTL, and only need to specify a new set of connection behaviors for the IOs of that module. Simply create a matching config within generators/firechip/src/main/scala/TargetConfigs that inherits your config defined in chipyard.

class FireSimRocketConfig extends Config(
  new WithDefaultFireSimBridges ++
  new WithDefaultMemModel ++
  new WithFireSimConfigTweaks ++
  new chipyard.RocketConfig)

Only 3 additional config fragments are needed.

  • WithFireSimConfigTweaks modifies your design to better fit the FireSim usage model. For example, FireSim designs typically include a UART. Technically, adding this in is optional, but strongly recommended.
  • WithDefaultMemModel sets the external memory model in the FireSim simulation. See the FireSim documentation for details.
  • WithDefaultFireSimBridges sets the IOBinders key to use FireSim’s Bridge system, which can drive target IOs with software bridge models running on the simulation host. See the FireSim documentation for details.