21264/Ev67 Response To System Probe And In-Flight Command Interaction - Compaq 21264 Hardware Reference Manual

•
Probes that invalidate locked blocks do not generate a ReadBlkMod command. The
21264/EV67 fails the STx_C instruction as defined in the Alpha Architecture
Handbook, Version 4
•
All read commands (RdBlk, RdBlkMod, Fetch, InvalToDirty) do not interact
because the 21264/EV67 does not yet own the block.
Table 4–33 21264/EV67 Response to System Probe and In-Flight Command Interaction
Pending Internal
21264/EV67
Command

21264/EV67 Response to System Probe and In-Flight Command Interaction

ReadBlk This case assumes that a WrVictimBlk command has been sent to the system and another
ReadBlkMod agent has performed a load/store instruction to the same address. The 21264/EV67 pro-
FetchBlk vides VAF hit information with the probe response so that the system can manage the race
InvalToDirty condition between the WrVictimBlk command from this processor and a possible WrVic-
WrVictimBlk timBlk command from the probing processor. This race condition can be managed by
either forcing the completion of the WrVictimBlk command to memory before allowing
the progress by the probing processor, or by killing the WrVictimBlk command in this
processor.
CleanToDirty This case assumes that a SetDirty command has been sent to the system environment
SharedToDirty because of a store instruction that hit in the 21264/EV67 caches and that another processor
has performed a load/store instruction to the same address. The 21264/EV67 provides
MAF hit information so that the system can correctly respond to the Set/Dirty command.
If the next state of the probe was Invalid (the other processor performed a store instruc-
tion), and the probe reached the system serialization point before the Set/Dirty command,
the system must either fail the Set/Dirty command or provide the updated data from the
other processor.
STCChangeToDirty This case is similar to case 2, except that the initiating instruction for the Set/Dirty com-
mand is a STx_C. An address match with an invalidating probe must fail the Set/Dirty
command. Delivering the updated data from the other processor is not an option because
of the requirements of the LDx_L/STx_C instruction pair.
Alpha 21264/EV67 Hardware Reference Manual
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System Port
Cache and External Interfaces
4–41