Accessing debug features
ARM®v8‑M processors can contain several programmable debug registers which control the debug features available to the software engineer. Not all these are visible to software. These registers are normally accessed through an external debugger, such as ARM DS-5, and through a Debug Access Port (DAP). This is what debug tools, for example, DS-5 and uLINK are used for.
Debug logic can only provide information on the current state of a halted processor, it cannot provide trace information (a history of what has executed just before and just after a particular trigger event).
Debug components like the Data Watchpoint and Trace unit (DWT), Instrumentation Trace Macrocell (ITM), and Embedded Trace Module (ETM), can be used to supply this information.