mcf5307cft90b Freescale Semiconductor, Inc, mcf5307cft90b Datasheet - Page 115

• Manufacturer Part Number: mcf5307cft90b
• Description: Mcf5307 Coldfire Integrated Microprocessor User
• Manufacturer: Freescale Semiconductor, Inc

Freescale Semiconductor, Inc.
Cache Operation
also written to external memory. The cache line state is unchanged. For copyback accesses,
the cache controller updates the cache line and sets the M bit for the line. An external write
is not performed and the cache line state changes to (or remains in) the modified state.
4.9.4 Cache Coherency
The MCF5307 provides limited cache coherency support in multiple-master environments.
Both write-through and copyback memory update techniques are supported to maintain
coherency between the cache and memory.
The cache does not support snooping (that is, cache coherency is not supported while
external or DMA masters are using the bus). Therefore, on-chip DMAs of the MCF5307
cannot access local memory and do not maintain coherency with the unified cache.
4.9.5 Memory Accesses for Cache Maintenance
The cache controller performs all maintenance activities that supply data from the cache to
the core, including requests to the SIM for reading new cache lines and writing modified
lines to memory. The following sections describe memory accesses resulting from cache
fill and push operations. Chapter 18, “Bus Operation,” describes required bus cycles in
detail.
4.9.5.1 Cache Filling
When a new cache line is required, a line read is requested from the SIM, which generates
a burst-read transfer by indicating a line access with the size signals, SIZ[1:0].
The responding device supplies 4 consecutive longwords of data. Burst operations can be
inhibited or enabled through the burst read/write enable bits (BSTR/BSTW) in the
chip-select control registers (CSCR0–CSCR7).
SIM line accesses implicitly request burst-mode operations from memory. For more
information regarding external bus burst-mode accesses, see Chapter 18, “Bus Operation.”
The first cycle of a cache-line read loads the longword entry corresponding to the requested
address. Subsequent transfers load the remaining longword entries.
A burst operation is aborted by an a write-protection fault, which is the only possible access
error. Exception processing proceeds immediately. Because the write cycle can be
decoupled from the processor’s issuing of the operation, error signaling appears to be
decoupled from the instruction that generated the write. Accordingly, the PC in the
exception stack frame represents the program location when the access error was signaled.
See Section 2.8.2, “Processor Exceptions.”
Chapter 4. Local Memory
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