Use when implementing a hardware block, protocol, peripheral, or ISA feature in ROHD and you should ground it in the authoritative spec, existing reference implementations, and reusable libraries you fetch first, instead of writing it from memory
Use when bringing up bare-metal or kernel code on a new architecture, SoC, or board (RISC-V, ARM, x86, ESP32) and it won't boot, hangs after boot, or faults early; covers trap vectors, MMU/PMP, syscall ABI, and boot ordering
Use when building or debugging a compiler backend, codegen, or assembler and you need to prove the generated machine code is correct by executing it on a real CPU or a fast emulator, not just inspecting the output
Use when verifying a hardware DUT (a CPU core, FPGA, or netlist) against a golden reference model, building coverage-guided fuzzing, or detecting where silicon diverges from a simulator like Spike, an emulator, or SPICE
Use when building or debugging a firmware and boot chain (RISC-V SBI, UEFI, ACPI, a bootloader handoff like Limine to an OS) or adding measured boot with a TPM, and a stage fails to hand off to the next
Use when loading a bitstream onto a physical FPGA and driving or observing it over JTAG or GPIO, especially bit-banged JTAG from a host like a Raspberry Pi, or when configuration silently fails
Use when synthesizing RTL to an FPGA with yosys/nextpnr (ECP5/Lattice and similar), fighting area or routing congestion, measuring Fmax, deciding why a design won't fit or route, or instantiating block RAM; covers the pre-pack vs post-pack metric trap
Use when writing, refactoring, or deciding how to test an HDL module, component, or IP block (ROHD, Chisel, SpinalHDL, Verilog, VHDL) and you need it parameterized, validated, and covered by exhaustive tests rather than a one-off