Specifications

Description
If the Nios II processor implements a direct mapped data
cache, flushd writes the data cache line that is mapped to the
specified address back to memory if the line is dirty, and then
clears the data cache line. Unlike flushda, flushd writes the
dirty data back to memory even when the addressed data is not
currently in the cache. This process comprises the following
steps:
• Compute the effective address specified by the sum of rA
and the signed 16-bit immediate value.
• Identify the data cache line associated with the computed
effective address. Each data cache effective address
comprises a tag field and a line field. When identifying the
data cache line, flushd ignores the tag field and only uses
the line field to select the data cache line to clear.
• Skip comparing the cache line tag with the effective address
to determine if the addressed data is currently cached.
Because flushd ignores the cache line tag, flushd flushes
the cache line regardless of whether the specified data
location is currently cached.
• If the data cache line is dirty, write the line back to memory.
A cache line is dirty when one or more words of the cache
line have been modified by the processor, but are not yet
written to memory.
• Clear the valid bit for the line.
If the Nios II processor core does not have a data cache, the
flushd instruction performs no operation.
Usage
Use flushd to write dirty lines back to memory even if the
addressed memory location is not in the cache, and then flush
the cache line. By contrast, refer to “flushda flush data cache
address”, “initd initialize data cache line”, and “initda initialize
data cache address” for other cache-clearing options.
For more information on data cache, refer to the Cache and
Tightly Coupled Memory chapter of the Nios II Software
Developer’s Handbook.
Exceptions
None
Instruction Type
I
Instruction Fields
A = Register index of operand rA
IMM16 = 16-bit signed immediate value
Bit Fields
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
A 0 IMM16
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
NII51017
2015.04.02
flushd
8-39
Instruction Set Reference
Altera Corporation
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