Compaq Using SysDc Commands, System Responses to 21264/EV68A Commands and Reactions

Models: EV68A

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Cache Coherency

4.5.4 Using SysDc Commands

Note the following:

The conventional response for RdBlk commands is SysDc ReadData or ReadD- ataShared.

The conventional response for a RdBlkMod command is SysDc ReadDataDirty.

The conventional response for ChangeToDirty commands is ChangeToDirtySuccess or ChangeToDirtyFail.

However, the system environment is not limited to these responses. Table 4–5shows all 21264/EV68A commands, system responses, and the 21264/EV68A reaction. The 21264/EV68A commands are described in the following list:

Rdx commands are generated by load or Istream references.

RdBlkModx commands are generated by store references.

The ChxToDirty command group includes CleanToDirty, SharedToDirty, and STC- ChangeToDirty commands, which are generated by store references that hit in the 21264/EV68A cache system.

InvalToDirty commands are generated by WH64 instructions that miss in the 21264/EV68A cache system.

FetchBlk and FetchBlkSpec are noncached references to memory space that have missed in the 21264/EV68A cache system.

Rdiox commands are noncached references to I/O address space.

Evict and STCChangeToDirty commands are generated by ECB and STx_C instructions, respectively.

Table 4–5shows the system responses to 21264/EV68A commands and 21264/EV68A reactions.

Table 4–5 System Responses to 21264/EV68A Commands and Reactions

21264/EV68A

 

 

CMD

SysDc

21264/EV68A Action

 

 

 

Rdx

ReadData

This is a normal fill. The cache block is filled and marked clean or

 

ReadDataShared

shared based on SysDc.

Rdx

ReadDataShared/Dirty

The cache block is filled and marked dirty/shared. Succeeding store

 

 

commands cannot update the block without external reference.

Rdx

ReadDataDirty

The cache block is filled and marked dirty.

Rdx

ReadDataError

The cache block access was to NXM address space. The 21264/

 

 

EV68A delivers an all-ones pattern to any load command and evicts

 

 

the block from the cache (with associated victim processing). The

 

 

cache block is marked invalid.

Rdx

ChangeToDirtySuccess

Both SysDc responses are illegal for read commands.

 

ChangeToDirtyFail

 

21264/EV68A Hardware Reference Manual

Cache and External Interfaces 4–11

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Compaq specifications Using SysDc Commands, System Responses to 21264/EV68A Commands and Reactions