Hardware Reference
In-Depth Information
Memories
Crosspoint
switch is open
000
001
010
(b)
011
Crosspoint
switch is closed
100
101
110
111
(c)
Closed
crosspoint
switch
Open
crosspoint
switch
(a)
Figure 8-29.
(a) An 8 × 8 crossbar switch. (b) An open crosspoint. (c) A closed
crosspoint.
UMA Multiprocessors Using Multistage Switching Networks
2 switch
shown in Fig. 8-30(a). This switch has two inputs and two outputs. Messages arri-
ving on either input line can be switched to either output line. For our purposes
here, messages will contain up to four parts, as shown in Fig. 8-30(b). The
Module
field tells which memory to use. The
Address
specifies an address within a mod-
ule. The
Opcode
gives the operation, such as
READ
or
WRITE
. Finally, the optio-
nal
Value
field may contain an operand, such as a 32-bit word to be written on a
WRITE
. The switch inspects the
Module
field and uses it to determine if the mes-
sage should be sent on
X
or on
Y
.
A
B
That ''something quite different'' can be based on the humble 2
×
X
Y
Module
Address Opcode
Value
(a)
(b)
Figure 8-30.
(a)A2
×
2 switch. (b) A message format.
2 switches can be arranged in many ways to build larger
multistage
switching networks
. One option is the no-frills, economy class
omega network
,
Our 2
×
