Atmel SpaceWire Router SpW-10X - Manual (Page 96)

Ref.: UoD_SpW-10X_
UserManual
Issue: 3.4
SpW-10X
SpaceWire Router
User Manual Date: 11 th
July 2008
Preliminary
96
In blocking allowed mode the network path is blocked until the destination node starts to accept data
again. Packets waiting to use the network path will wait indefinitely.
In watchdog timer mode the router will timeout and the network path will be cleared so other packets
can use the path.
Blocking Allowed Mode
What happens when Blocking Allowed mode is being used and a destination node becomes blocked
is illustrated in Figure 8-14 to Figure 8-16. In this example two routing switches, R1 and R2, are
connected to form a network and only SpaceWire ports 1 to 6 are shown for clarity.
a) A packet arrives at port 3 of routing switch R1 destined for port 4 and then port 5 of R2 (as
shown by the path address 4, 5 at the head of the packet.
R1
1
2
3
4
5
6
(a)
4 5
R2
1 4
2
3
5
6
Figure 8-14 Destination Node Blocked (a)
b) The packet is routed towards its destination but during packet transfer the destination stalls
and does not accept any more data. The network path is blocked and the packet waiting at R1
port 2 is also blocked
R1
1
2
3
4
5
6
(b)
R2
1 4
2
3
5
6
4 4
Figure 8-15 Destination Node Blocked (b)
c) The path between routing switch R1 port 4 and routing switch R2 port 1 is now blocked. While
the first packet is routed another packet arrives at port 2 on router R1 with destination port 4
on router R1 and destination port 4 on router R2. The packet must wait as the ports are
currently busy and can only be routed if the downstream node starts receiving data again.