neorv32/sw/example/floating_point_test

NEORV32 Zfinx Floating-Point Extension

The RISC-V Zfinx single-precision floating-point extensions uses the integer register file x instead of the dedicated floating-point f register file (which is defined by the RISC-V F single-precision floating-point extension). Hence, the standard data transfer instructions from the F extension are not available in Zfinx:

• floating-point load/store operations (FLW, FSW) and their compressed versions
• integer register file x <-> floating point register file f move operations (FMV.W.X, FMV.X.W)

ℹ️ More information regarding the RISC-V Zfinx single-precision floating-point extension can be found in the officail GitHub repo: github.com/riscv/riscv-zfinx.

⚠️ The RISC-V Zfinx extension is not officially ratified yet, but it is assumed to remain unchanged. Hence, it is not supported by the upstream RISC-V GCC port. Make sure you do not use the f ISA attribute when compiling applications that use floating-point arithmetic (-march=rv32i*f* is NOT ALLOWED!).

Intrinsic Library

The NEORV32 Zfinx floating-point extension can still be used using the provided intrinsic library. This library uses "custom" inline assmbly instructions wrapped within normal C-language functions. Each original instruction of the extension can be utilized using an according intrinsic function.

For example, the floating-point addition instruction FADD.S can be invoked using the according intrinsic function:

float riscv_intrinsic_fadds(float rs1, float rs2)

The pure-software emulation instruction, which uses the standard builtin functions to execute all floating-point operations, is available via wrapper function. The emulation function for the FADD.S instruction is:

float riscv_emulate_fadds(float rs1, float rs2)

The emulation functions as well as the available intrinsics for the Zfinx extension are located in neorv32_zfinx_extension_intrinsics.h.

The provided test program main.c verifies all currently implemented Zfinx instructions by checking the functionality against the pure software-based emulation model (GCC soft-float library).