3.4.3.6 PBU Performance Monitoring

Each word of data requested on the CPU instruction bus will be sourced either from the ISB or the Instruction Cache and not the external NVM. This ensures that each fetch of program data can be completed in minimal time, which maximizes application performance.

Program data that are not already present in the ISB or cache must be fetched from the NVM, which takes additional cycles and decreases overall application performance. Once program data in a particular NVM program word has been consumed by the CPU, it is stored in the Instruction Cache for later use. The exceptions to this are program data with uncorrectable errors, security violations, or debugger executive program data. Once stored, the program data will be available for later reuse in the Instruction Cache until those contents are erased and replaced with another program data word.