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.

Details

The dcbst instruction writes the contents of a block in the data cache to main storage if the block is marked as modified. The effective address (EA) is calculated as the sum of RA and RB.

Pseudocode Operation

EA <- (RA) + (RB)
if EA is in a block that is Memory Coherence Required and the block is modified in any processor's data cache then
    write modified locations to main storage
    mark the block as no longer modified
else if EA is in a block that is not Memory Coherence Required and the block is modified in this processor's data cache then
    write modified locations to main storage
    mark the block as no longer modified

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.

Extended Mnemonics

Extended Mnemonic Equivalent Instruction

Example

dcbst 0, r3

Encoding

Binary Layout
31
0
/
6
RA
11
RB
21
54
/
 
Format X-form
Opcode 0x7C00006C
Extension Base

Operands

  • RA
    Base Address
  • RB
    Index Address