MIPS R4000 Microprocessor User's Manual A-43
CPU Instruction Set Details
Write back from a primary cache goes to the secondary cache (if there is
one), otherwise to memory. Write back from a secondary cache always
goes to memory. A secondary write back always writes the most recent
data; the data comes from the primary data cache, if present, and modified
(the W bit is set). Otherwise the data comes from the specified secondary
cache. The address to be written is specified by the cache tag and not the
translated physical address.
TLB Refill and TLB Invalid exceptions can occur on any operation. For
Index operations (where the physical address is used to index the cache
but need not match the cache tag) unmapped addresses may be used to
avoid TLB exceptions. This operation never causes TLB Modified or
Virtual Coherency exceptions.
Bits 17...16 of the instruction specify the cache as follows:
Code Name Cache
0 I primary instruction
1 D primary data
2 SI secondary instruction
3 SD secondary data (or combined instruction/data)
(continued)
CACHE
ac
e
CACHE
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