Atmel SpaceWire Router SpW-10X - Manual (Page 97)

Ref.: UoD_SpW-10X_
UserManual
Issue: 3.4
SpW-10X
SpaceWire Router
User Manual Date: 11 th
July 2008
Preliminary
97
R1
1
2
3
4
5
6
(c)
R2
1 4
2
3
5
6
4 4
Figure 8-16 Destination Node Blocked (c)
Watchdog timer mode
What happens when the routers are in Watchdog Timer mode and a destination becomes blocked is
illustrated in Figure 8-17to Figure 8-20. 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
R1
1
2
3
4
5
6
(a)
4 5
R2
1 4
2
3
5
6
4 4
Figure 8-17 Destination Node Blocked: Watchdog Mode (a)
b) The packet is routed towards its destination but during packet transfer the destination stalls
and does not accept further 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 8-18 Destination Node Blocked: Watchdog Mode (b)
c) At routing switches R1 and R2 the watchdog timers detect the packet has blocked for the
specified timeout period. The packet is then discarded by the routers by spilling the data at the
input port and appending an EEP to the data at the output ports. Once the packet has been
removed from the network an EEP is ready to be appended to routing switch R2 port 5 when
buffer space is available and the network path between routing switch R1 port 4 and routing
switch R2 port 1 is available.