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29 September 1997 – Subject To Change
Initialization and Configuration
7–9
External Interface Initialization
7.6.1 Icache Initialization
The Icache is not kept coherent with memory. When it is necessary to make it coher-
ent with memory, the following procedure is used. The CALL_PAL IMB function
performs this function by using this procedure.
1.
Execute an MB instruction. This forces all write data in the write buffer into
memory.
–
Stall until write buffer is drained.
–
Carry load or issue a HW_MFPR from any MTU IPR.
2.
Write to IC_FLUSH_CTL with an HW_MTPR to flush the Icache.
3.
Execute a total of 44 NOP instructions (BIS r31,r31,r31) to clear the prefetch
buffers and IDU pipeline. The 44 NOP instructions must start on an INT16
boundary. Pad with additional NOP instructions if necessary.
7.6.2 Flushing Dirty Blocks
During a power failure recovery, dirty blocks must be flushed out of the backup
cache (Bcache).
To flush out dirty blocks from the Bcache on power failure, the following sequence
must be used to guarantee that all the dirty blocks have been written back to main
memory:
Perform loads at a stride of Bcache block size = 2
×
size of the Bcache
7.7 External Interface Initialization
After reset, the cache control and bus interface unit (CBU) is in the default configu-
ration dictated by the reset state of the IPR bits that select the configuration options.
The CBU response to system commands and internally generated memory accesses
is determined by this default configuration. System environments that are not com-
patible with the default configuration must use the SROM Icache load feature to ini-
tially load and execute a PALcode program. This program configures the external
interface control (CBU) IPRs as needed.