FlushDataCache
Because flushing this cache degrades performance of the CPU, this routine
should be called only when absolutely necessary.
Notes: Be sure to check that the trap _HWPriv is implemented before calling this
to determine whether a trap is implemented. If you call this routine and
_HWPriv is not implemented, you application will crash.
A cache may contain stale data whenever information in main memory is
changed and that information is already cached in the micro processor's data
cache. The MC68030 has a write- through cache. This means that any
data written to the cache is immediately written out to main memory. You
need to flush a write-through cache if you write directly to main memory.
This can cause the information in the data cache to become stale.
The MC68040 has a copy-back cache. Any data written to the cache is
written to main memory only when necessary to make room in the cache for
data accessed more recently or when the cache is explicitly flushed. A
copy-back cache needs to be flushed if you write data that is to be read by
non-CPU devices that access RAM directly. A copy-back cache can also
lead to use of invalid instructions if the stale data in RAM contains
executable code. When fetching instructions, the CPU looks in the
instruction cache and, if necessary, in main memory, but not in the data
the data cache and then the instruction cache of a processor with a
copy-back cache, such as the MC68040. This operation should be
performed whenever self-modifying code is used.