Service manual

Cache Coherency B-33
3. The Fwd Rd Mod probe packets resulting from each Read-type command are
then issued to the ArbBus of the QBB of the dirty processor. The Fwd Rd
Mod is sent directly to the dirty processor and visits:
• The DTag to determine if any of the CPUs in the dirty processor’s
QBB have copies of the addressed block.
• The IOP tag store to determine if the IOP in the dirty processor’s QBB
has a copy (clean or dirty) of the addressed block.
• The TTT to determine if invalidates should be issued to those
processors (CPU and IOP) that have copies of the addressed block.
4. The invalidate probe packets resulting from each Read Mod-type command
are then issued to the ArbBus of any QBB with a shared processor. As the
invalidate is issued to the ArbBus, it visits:
• The DTag to determine which of the CPUs in the QBB have copies.
• The IOP tag store to determine if the IOP has a copy of the block.
• The TTT to determine if invalidates should be issued to those
processors (CPU and IOP) that have copies of the addressed block.
5. The Q1 response packets resulting from Read Mod-type commands are
issued to the ArbBus of the requesting processor’s QBB. They visit:
• The DTag to update the DTag state (only if the requesting processor is
a CPU), and to determine if any of the CPUs in the requesting
processor’s QBB have copies of the addressed block.
• The IOP tag store to update the IOP tag state (only if the requesting
processor is the IOP), and/or to determine if the IOP in the requesting
processor’s QBB has a copy of the addressed block.
• The TTT to clear/update the TTT MAF state and to determine if
invalidates should be issued to those processors (CPU and IOP) that
have copies of the addressed block.
6. The Q2 response packets resulting from Read-type commands are issued to
the ArbBus of the requesting processor’s QBB. They visit:
• The DTag to update the state if the requesting processor is a CPU.
• The IOP tag store to update the IOP tag state if the requesting
processor is the IOP.
• The TTT to clear/update the TTT MAF state.