Service manual

B-32 AlphaServer GS80/160/320 Service Manual
B.10.5 Global (Remote) Read Modify Transactions
Figure B– 10 Read Mod Coherency Store Flow
Q0: Visit TTT
via GPLink
Q0
Q0Vic
Q1
Q1
Response
Packet
Q1
Probe
Packet
(Fwd Rd or Inval)
Q2
Dirty
Data
Q1
Probe
Packet
(Inval)
Q1: Visit TTT,
Dtag and IOP
Tag store, via
ArbBus.
Q2: Visit Dtag,
TTT and IOP
Tag store via
ArbBus.
Source QBB
Q0: Visit Directrory
Dtag, TTT and
IOP Tag store
via ArbBus.
Home QBB
Q1: Visit Dtag, TTT and
IOP Tag store
via ArbBus.
QBB of Shared Processor
Q1: Directory steers Fwd
Rd directly to Dirty
Processor.
Visit TTT, Dtag and
IOP Tag Store via
ArbBus
QBB of Dirty Processor
Remote Read Mod and Read Vic Mod commands use the system coherency
storage elements as illustrated in Figure B–10 and described by the following
sequence of events.
1. Each Read Mod-type command first visits the TTT via the GPLink, for the
purpose of creating a TTT MAF entry.
2. Each Read Mod-type command is then issued to the ArbBus of the home
QBB by means of the QS Arb. It visits:
• The DTag to determine both if the addressed block is dirty in the
home QBB and if any of the CPUs in the home QBB have copies.
• The directory to determine both if the addressed block is dirty in
another QBB and if any other QBBs have copies.
• The IOP tag store to determine if the home IOP has a copy (clean or
dirty) of the addressed block.
• The TTT to determine if the addressed block is in a transient state.