7.2. The RISC-V ISA Simulator (Spike)
Spike is the golden reference functional RISC-V ISA C++ sofware simulator. It provides full system emulation or proxied emulation with HTIF/FESVR. It serves as a starting point for running software on a RISC-V target. Here is a highlight of some of Spikes main features:
Multiple ISAs: RV32IMAFDQCV extensions
Multiple memory models: Weak Memory Ordering (WMO) and Total Store Ordering (TSO)
Privileged Spec: Machine, Supervisor, User modes (v1.11)
Single-step debugging with support for viewing memory/register contents
Multiple CPU support
Highly extensible (add and test new instructions)
In most cases, software development for a Chipyard target will begin with functional simulation using Spike (usually with the addition of custom Spike models for custom accelerator functions), and only later move on to full cycle-accurate simulation using software RTL simulators or FireSim.
Spike comes pre-packaged in the RISC-V toolchain and is available on the path as
More information can be found in the Spike repository.
Chipyard contains experimental support for simulating a Spike processor model with the uncore, similar to a virtual-platform. In this configuration, Spike is cache-coherent, and communicates with the uncore through a C++ TileLink private cache model.
make CONFIG=SpikeConfig run-binary BINARY=hello.riscv
Spike-as-a-Tile also supports Tightly-Coupled-Memory (TCM) for the SpikeTile, in which the main system memory is entirely modeled within the Spike tile, allowing for very fast simulatoin performance.
make CONFIG=SpikeUltraFastConfig run-binary BINARY=hello.riscv
Spike-as-a-Tile can be configured with custom IPC, commit logging, and other behaviors. Spike-specific flags can be added as plusargs to
make CONFIG=SpikeUltraFastConfig run-binary BINARY=hello.riscv EXTRA_SPIKE_FLAGS="+spike-ipc=10000 +spike-fast-clint +spike-debug" LOADMEM=1
+spike-ipc=: Sets the maximum number of instructions Spike can retire in a single “tick”, or cycle of the uncore simulation.
+spike-fast-clint: Enables fast-forwarding through WFI stalls by generating fake timer interrupts
+spike-debug: Enables debug Spike logging
+spike-verbose: Enables Spike commit-log generation