Service manual

Cache Coherency B-9
B.6 Virtual Channels
When mapping processor request activity onto a switch-based distributed
shared memory system, it is necessary to create switch packets to support
processor commands, command responses, and probes.
The GS80/160/320 distributed shared memory systems operate by passing
message packets between QBBs. A variety of message types are used to support
the wide variety of system operations. These message types include processor
command packets, command response packets, and probe command packets.
These messages that are passed about the system are organized into a
framework referred to as virtual channel flow control. This framework
organizes the messages into groups, and transmits messages from different
groups across independently flow controlled queuing channels. These queuing
channels are referred to as “virtual channels” because they are independent, but
often share the same interconnect resources to transmit messages.
Virtual
Channel
Name Description
# of
Packet
Types
QIO
QIO carries processor command packets only. In
particular, QIO carries all reads and writes to
I/Oaddress space including CSR accesses.
6
Q0Vic
Q0Vic carries processor command packets only. In
general, Q0Vic carries all memory space processor
command packets that transfer data.
6
Q0
Q0 carries processor command packets only. In general,
Q0 carries all memory space processor command
packets that do not transfer data.
13
Q1
Q1 carries command response packets and probe
packets. Command response packets may or may not
have data associated with them.
37
Q2
Q2 carries command response packets only. All Q2
packets have data associated with them.
8