Operands of locked instructions (CAS and TAS) and operand references while the lock bit
in the bus control register is set which miss in the data cache do not allocate for reads or
writes regardless of the caching mode, and therefore will bypass the cache. Locked instruc-
tions that hit in the data cache invalidate a matching valid entry or will push and invalidate a
matching dirty entry. The locked operand access will then bypass the cache.
The cache control register (CACR) is a 32-bit register which contains control information for
the instruction and data caches. A MOVEC sets all of the bits in the CACR. A hardware reset
clears the CACR, disabling both caches; however, reset does not affect the tags, state infor-
mation, and data within the caches. The CACR is illustrated in Figure 5-5.
EDC—Enable Data Cache
0 = Data cache is disabled.
1 = Data cache is enabled.
NAD—No Allocate Mode (Data Cache)
0 = Read and write misses will allocate in the data cache.
1 = Read and write misses will not allocate in the data cache.
ESB—Enable Store Buffer
0 = All writes to writethrough or cache-inhibited imprecise pages will bypass the store
buffer and generate bus cycles directly.
1 = The four entry first-in-first-out (FIFO) store buffer to the MC68060 is enabled. This
buffer is used to defer pending writes to writethrough or cache-inhibited imprecise
pages to maximize performance.
Locked write accesses and accesses to cache-inhibited precise pages always bypass the
store buffer.
DPI—Disable CPUSH Invalidation
0 = Each cache line is invalidated as it is pushed. Affects only the data cache.
1 = CPUSHed lines remain valid in the cache.
FOC—1/2 Cache Operation Mode Enable (Data Cache)
0 = The data cache operates in normal, full-cache mode.
1 = The data cache operates in 1/2-cache mode.
31 30 29 28 27 26 24 23 22 21 20 16 15 14 13 12 0
EDC NAD ESB DPI FOC 0 0 0 EBC CABC CUBC 0 0 0 0 0 EIC NAI FIC 0 000000000000
Figure 5-5. Cache Control Register
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