Using Sysdc Commands; System Responses To 21264/Ev68A Commands And Reactions - Compaq EV68A Hardware Reference Manual

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 4–5 shows 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 4–5 shows 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
Rdx ReadData
ReadDataShared
Rdx ReadDataShared/Dirty
Rdx ReadDataDirty
Rdx ReadDataError
Rdx ChangeToDirtySuccess
ChangeToDirtyFail
21264/EV68A Hardware Reference Manual
21264/EV68A Action
This is a normal fill. The cache block is filled and marked clean or
shared based on SysDc.
The cache block is filled and marked dirty/shared. Succeeding store
commands cannot update the block without external reference.
The cache block is filled and marked dirty.
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.
Both SysDc responses are illegal for read commands.
Cache Coherency
Cache and External Interfaces
4–11