What improvement in performance does the cache memory give you on the SH2 ?
The cache is a basic 256 entry direct map replacement cache. This means the hit rate is not as high as say the SH3 cache. However reasonable performance increases can be achieved especially when accessing slow or narrow external memory. Switching cache on effectively gives you the performance of 16 bit wide memory from 8 bit wide memory. Only instructions and PC relative data are cached it is not a data cache. Actual speedups will depend on user code however the diagram below shows the speedup gained using the Dhrystone benhmark using 3 state memory. Please note that when the cache is enabled the 4KB of internal RAM is split into 2KB of user RAM amd 1KB of cache