Sun Microelectronics
84
UltraSPARC User’s Manual
7.4 SYSADDR Bus Arbitration Protocol
This section specifies the distributed arbitration protocol for driving a request
packet on the SYSADDR bus.
7.4.1 SYSADDR Bus Interconnection Topology
SYSADDR accommodates a maximum of four bus masters (which can be either
UltraSPARCs or I/O ports), as well as a System Controller (SC).
A master UltraSPARC cannot send a request directly to a slave. All transactions
are received by the SC and either serviced directly or forwarded to the proper re-
cipient. The SC delivers a transaction to a specific interconnect slave interface by
asserting that slave’s unique Addr_Valid signal. Note that in this discussion,
Memory is considered a slave.
A distributed arbitration protocol determines the current driver for the
SYSADDR bus and Addr_Valid. Although each Addr_Valid has only two poten-
tial drivers, the same enable logic can and should be used for both. Holding am-
plifiers in the System Controller must maintain the last state of Addr_Valid
whenever UltraSPARC or the SC stop driving it.
Figure 7-10 illustrates the interconnection topology for the SYSADDR bus. With
this topology, the arbiter logic can be implemented efficiently, without any inter-
nal muxing or demuxing of the input or output request signals.
Figure 7-10
SYSADDR Bus Interconnection Topology
SC_RQ
Req<3>
Req<2>
Req<1>
Req<0>
SYSADDR<35:0>
System Controller
Addr_Valid<3>
Addr_Valid<2>
Addr_Valid<1>
Addr_Valid<0>
port_ID<4:0>
port_ID<4:0>
port_ID<4:0>
port_ID<4:0>
1:0=0
1:0=1
1:0=2
1:0=3
Node_RQ<2>
Node_RQ<1>
Node_RQ<0>
Node_RQ<2>
Node_RQ<2>
Node_RQ<2>
Node_RQ<1>
Node_RQ<1>
Node_RQ<1>
Node_RQ<0>
Node_RQ<0>
Node_RQ<0>
Node
x_RQ
Node
x_RQ
Node
x_RQ
Node
x_RQ
RESET_L
UltraSPARC
0
UltraSPARC
1
UltraSPARC
2
UltraSPARC
3
SC_RQ
SC_RQ
SC_RQ
SC_RQ
RESET_L
RESET_L
RESET_L
RESET_L
Addr_V
alid<3>
Addr_V
alid<1>
Addr_V
alid<2>
Addr_V
alid<0>
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com