System Port

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

Cache and External Interfaces 4–41

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Compaq 21264, EV67 specifications System Port