Copperline 0.9.0 improves Amiga FPU accuracy for timing-sensitive software

Copperline 0.9.0 landed with a major 68881 and 68882 floating-point accuracy pass that targets the Amiga software most likely to break when hardware behavior is only approximate. The update was posted on July 2, and it pushes the Rust-based emulator closer to the original machine’s quirks rather than leaning on per-game fixes.

Copperline is a cycle-driven Amiga emulator for OCS, ECS, and AGA that models the chip bus, Copper, blitter, Paula, and CIA at the colour-clock level. The 0.9.0 release moves the FPU core to an 80-bit extended register file and adds softfloat paths and packed-decimal real support. It also revises math handling and FMOVECR constants. The release reaches extended-precision operations, memory and immediate-source monadic instructions, exponential and logarithmic functions, trigonometric and inverse-trigonometric kernels, hyperbolic functions, FPCR rounding propagation, FPSR exception reporting, and FMOD/FREM quotient handling. Older save states no longer load with the new FPU snapshot format.

Users can switch between keyboard joystick emulation and a real gamepad from the status bar, menu, launcher, or config file. Save-state startup no longer requires opening the original ROM first. Hard-disk volume names are handled more cleanly too, including directory-based drives and generated disk images.

The emulator can boot with a bundled AROS boot ROM, but commercial Amiga software still needs the proper original ROM and media images.

Under the hood, Copperline’s recent work also includes another pass on CIA timer one-shot handling, floppy motor timing, keyboard handshakes, Paula POTxDAT counters, display fetch timing, sprite latches, collision accumulation, and related video logic. It boots Kickstart and runs timing-sensitive OCS and AGA software from its regression set at real speed, and it now includes a debugger window that visualizes chip-bus ownership, DMA spans, CPU waits, blitter pressure, and display fetch activity, plus remote GDB debugging.