SPRUJ79 November 2024 F29H850TU , F29H859TU-Q1
Upon the first program access, data is fetched from memory and presented to the CPU. On every access to ROM, 256 bits are fetched from the address that is aligned to the 256-bit boundary. The prefetch buffer can store up to two 256-bit words and stores both ECC and data. The ROM memory controller prefetches data from the next sequential 256-bit boundary-aligned address as long as there is an empty slot in the prefetch buffer. This is known as a prefetch access. Prefetch and program accesses are lower priority than data accesses as shown in Arbitration section.
This process does not start until ROM receives the first program access. After reset, the prefetch logic is idle until a program access with a discontinuity is received. This discontinuity is indicated by the CPU.
The prefetch buffer is flushed whenever a CPU program access with a discontinuity anywhere on the memory map occurs, not just when ROM is accessed.