US Patent 7437616 Dual CPU on-chip-debug low-gate-count architecture with real-time-data tracing

The same microcontroller chip is configured to be either a Target version or a Link version of a microcontroller. The Target version runs an application program. To debug the Target microcontroller, the Link version of the microcontroller functions as a master debug microcontroller to the slave Target microcontroller running the application program. The Link microcontroller runs an interface translator program between a Host computer that runs a debug program, and the Target microcontroller. The Link microcontroller communicates with the Target microcontroller using a fast, 2-wire interface. The Link microcontroller communicates with the Host computer through a general purpose interface.