Atmel SpaceWire Router SpW-10X - Manual (Page 92)

Ref.: UoD_SpW-10X_
UserManual
Issue: 3.4
SpW-10X
SpaceWire Router
User Manual Date: 11 th
July 2008
Preliminary
92
8.3.3 Group Adaptive Routing
The SpaceWire router routing table can be set up to support group adaptive routing of packets.
Setting the routing table contents is described in section 9.3.
In group adaptive routing a set of output ports can be assigned to a logical address. When a packet
arrives with the logical address the routing table is checked for the set of output ports which the packet
can use. The routing control logic then checks the possible router output ports to determine if any of
them are free and ready to use. As soon as one of the possible output ports associated with the
logical address of the packet is free and ready to use then the packet is routed through that output
port. If all the set of output ports which the logical address packet can use are free then the router
chooses the lowest numerical output port number to route the packet.
Arbitration is performed on group adaptive routing packets as defined in section 8.3.2.
The following sub-section consider various situations that can occur during group adaptive routing.
8.3.3.1 Normal Group adaptive routing
In normal group adaptive routing the lowest numerical output port in the group that is ready to use is
used to transfer the packet. This is illustrated in Figure 8-10.
R1
1
2
3
4
5
6
76
76
R1
1
2
3
4
5
6
Group adaptive routing packet with address 76 arrives at port 1
Group adaptive routing packet with address 76 arrives at port 3 Routing logic assigns port 4 to port 1
And port 5 to port 3
Address 76 – Routing table entry
Header Deletion disabled
Port 4
Port 5
Port 6
76
76
1 2
Figure 8-10 Normal group adaptive routing
8.3.3.2 Group adaptive routing when busy
The situation when some of the output ports in group are busy is illustrated in Figure 8-11. Logical
address 76 has group adaptive routing set up so that packets with that address can use output ports
4, 5 or 6. In Figure 8-11 output ports 4 and 5 are busy, and port 6 is not being used. When a packet
with logical address 76 arrives at input port 1 it is routed immediately to output port 6.