Microcode inside the Intel 8087 floating-point chip: register exchange
4 hours ago
- #Intel 8087
- #Floating-Point Architecture
- #Microcode Reverse-Engineering
- Intel introduced the 8087 floating-point chip in 1980, significantly accelerating floating-point operations.
- The 8087 established the floating-point standard used in modern processors.
- It uses microcode to implement complex algorithms for functions like square roots and exponentials.
- The Opcode Collective is reverse-engineering the 8087's microcode, including the FXCH instruction.
- FXCH exchanges two floating-point registers and involves 14 micro-instructions, more than expected.
- The chip's architecture includes a microcode ROM, a datapath for calculations, and stack-based registers with tags.
- Microcode handles exceptions like invalid operations, with options to interrupt or mask and continue.
- Extracting microcode involved imaging the ROM and analyzing transistor patterns to decode instructions.
- Reverse-engineering the 8087's microcode reveals its complex and optimized design for floating-point computations.