SNES Coprocessors: DSP-1 and Friends

The blog post discusses the coprocessors used in the Super Nintendo Entertainment System (SNES), focusing primarily on the DSP-1. The DSP-1, introduced with the game Pilotwings in 1990, is an NEC μPD77C25 DSP designed to assist with 3D calculations, enabling games like Super Mario Kart to maintain smooth frame rates. The DSP operates at 8 MHz and can execute one instruction per cycle, performing signed 16-bit multiplications efficiently. It features 6KB of program ROM and 2KB of data ROM, utilizing lookup tables for mathematical functions.

The communication between the SNES CPU and the DSP-1 occurs through two 8-bit registers, with the DSP-1 program structured to respond to commands from the CPU. The post also mentions other coprocessors like DSP-2, DSP-3, and DSP-4, each tailored for specific games, and the ST010 and ST011, which use a more advanced μPD96050 DSP. These later coprocessors support higher memory capacities and additional instructions.

Emulation of these coprocessors varies, with many emulators using high-level emulation (HLE) due to the complexity of the DSP-1 program ROM. Some modern emulators also implement low-level emulation (LLE) for greater accuracy. The post concludes with a brief mention of the ST018 coprocessor, which features a 32-bit ARMv3 CPU but is less commonly supported in emulators due to its specific application in a shogi game.