ARM processor cores implementing the v7-M architecture, currently Cortex-M3 and Cortex-M4, include a component called the "Flash Patch and Breakpoint" Unit (FPB). Besides being used by debug tools to provide a hardware breakpoint mechanism, FPB provides a mechanism for patching immutable program code or literal constants in firmware by redirecting memory accesses. This paper will show you an MCU-vendor independent approach to do this.
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