dcbst

Data Cache Block Store

dcbst RA, RB

Writes the cache block to main memory if it is modified (Clean), but keeps it in the cache.

Encoding

Binary Layout

31

0:5

/

6:10

RA

11:15

RB

16:20

54

21:30

/

31

 

Format X-form

Opcode 0x7C00006C

Extension Base

Operands

• RA
  Base Address
• RB
  Index Address

Example

dcbst 0, r3

// Ensure RAM has latest data for r3.

Related

More in Base

Reference

View in PowerISA v3.1C Specification ↗ OPF Power ISA v3.1C

Description

Writes a cache block containing the byte addressed by RA+RB to main memory if the block is modified, then keeps the block in the cache in a clean state. This instruction is used to synchronize cache contents with memory without invalidating the cache line. No condition registers or status fields are affected.

Operation

EA ← (RA) + (RB)
CacheBlock ← CacheBlock at EA
if CacheBlock.Modified then
  WriteToMemory(CacheBlock)
  CacheBlock.Modified ← 0
end if

Extended Mnemonics

Extended Mnemonic	Equivalent Instruction

Programming Note

Data Cache Block Store to Persistent Storage is encoded as a variant of Data Cache Block Flush. The extended mnemonic (dcbstps) indicates the intended function.