They exposed a bus on one of their Cortex-M cores, so you can add custom instructions when building an ASIC.
Perhaps more importantly, they also changed their licensing to allow custom instructions.
Perhaps more importantly, they also changed their licensing to allow custom instructions.
Later there was no real bus anymore (486 SX "FPU" replaced the main CPU) or the only(?) kind of coprocessor ever used, the FPU, became integrated into the CPU.