Microcode inside the Intel 8087 floating-point chip: register exchange
Summary
Ken Shirriff's blog analyzes the 8087 microcode, focusing on the FXCH instruction and how it exchanges the top-of-stack value with a stack position. It describes the microcode structure, the use of temporary registers, and exception handling between microcode and hardware. The piece also covers how the microcode was reverse-engineered from ROM images and the challenges of mapping transistors to micro-instruction bits, with links to the GitHub repository for deeper detail.