9.3 Overview
When running the Prefetch module at high-clock rates, insert the Wait states into Program Flash Memory (PFM) read transactions to meet the access time of the PFM. The user can hide the Wait states to the core by prefetching and storing the instructions in a temporary holding area that the CPU can access quickly. Although, the data path to the CPU is 32 bits wide, the data path to the PFM is 128 bits wide. This wide data path provides the same bandwidth to the CPU as a 32-bit path running at four times the frequency.
The Prefetch module holds a subset of PFM in temporary holding spaces known as lines. Each line contains a tag and data field. Normally, the lines hold a copy of what is currently in memory to make instructions or data available to the CPU without the Wait states.
The CPU or a peripheral may request the data located in the PFM. If the requested data is not currently stored in the Prefetch module line, a read is performed to the PFM at the correct address, and the data is supplied to the Prefetch module and to the CPU or peripheral. If the requested data is stored in the Prefetch module and is valid, the data is supplied to the CPU or peripheral without Wait states.
