ISA

Embedded platform discussions often use different words as if they meant the same thing.

“This project uses ARM.” “This chip is RISC-V.” “This core supports Linux.” “This board has an MMU.” “Interrupts are different on this architecture.” “This toolchain is incompatible.” Some of these statements are true, and some are only half true. The problem is that they often collapse ISA, CPU core, privileged architecture, SoC, board, and software platform into one layer.

Embedded software often fails in places that do not look architecture-related at first.

A firmware image is flashed but never reaches main(). An exception handler is never entered. A Linux program reports Exec format error. A driver gives a buffer to DMA and then reads stale data. Unaligned access works on one chip and becomes a hard fault on another. The same assembly startup code fails completely on a different profile.