Motorola M68000 Betriebsanweisung PDF herunterladen (Seite 219)

The 68030 205

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Figure 22 68030 Data Cache. (Courtesy of Motorola, Inc)

we update both the cache and the physical memory for each write to

an address contained in the cache. This latter technique is called a write

through.

The first technique has the advantage that fewer writes to physical

memory are needed if the data in the cache is updated more than

once. Only one physical update is needed for many cache updates. The

disadvantage is that considerably more complex hardware is required.

The processor must keep track of which addresses in the cache have been

modified. The write through cache is a simpler design. Since the normal

programming method is to use registers for counters and addressing inside

loops, the penalty for the write through cache is not as great as one might

think.

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