Specifications

Description
If the Nios II processor implements a direct mapped data
cache, initda clears the data cache line without checking for
(or writing) a dirty data cache line that is mapped to the
specified address back to memory. Unlike initd, initda clears
the cache line only when the addressed data is currently cached.
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
line, initda uses both the tag field and the line field.
• Compare the cache line tag with the effective address to
determine if the addressed data is currently cached. If the
tag fields do not match, the effective address is not
currently cached, so the instruction does nothing.
• Skip checking if the data cache line is dirty. Because initd
skips the dirty cache line check, data that has been modified
by the processor, but not yet written to memory is lost.
• Clear the valid bit for the line.
If the Nios II processor core does not have a data cache, the
initda instruction performs no operation.
Usage
Use initda to skip writing dirty lines back to memory and to
flush the cache line only if the addressed memory location is
currently in the cache. By contrast, refer to “flushd flush data
cache line”, “flushda flush data cache address”, and “initd
initialize data cache line” on page 8–55 for other cache-clearing
options. Use initda with caution because it does not write
back dirty data.
For more information on the Nios II data cache, refer to the
Cache and Tightly Coupled Memory chapter of the Nios II
Software Developer’s Handbook.
Exceptions
Supervisor-only data address
Fast TLB miss (data)
Double TLB miss (data)
MPU region violation (data)
Unimplemented instruction
Instruction Type
I
Instruction Fields
A = Register index of operand rA
IMM16 = 16-bit signed immediate value
NII51017
2015.04.02
initda
8-45
Instruction Set Reference
Altera Corporation
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