18.1.4. External debug

A complex system requires much of its hardware and software to be functional before any standard interfaces can be used for debug. It is very important to get debug on a system without relying on the system being debugged. For this you need reliable external debug, that is, hardware-assisted, run-control debug and trace features. All of this can be controlled without the need for software operating on the platform but often this is needed very early in the product design cycle.Self-hosted tools usually require layers of software support, making it difficult to debug parts of the software, or making debugging too invasive for diagnosing some kinds of bug. Low-cost external debug interfaces, such as Serial Wire Debug (SWD), also help extend the range of applications where external debug is attractive. See CoreSight for more information.

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