Atmel SpaceWire Router SpW-10X - Manual (Page 98)

Ref.: UoD_SpW-10X_
UserManual
Issue: 3.4
SpW-10X
SpaceWire Router
User Manual Date: 11 th
July 2008
Preliminary
98
1
2
3
4
5
6
(c)
1 4
2
3
5
6
4 4
EEP
R1 R2
Figure 8-19 Destination Node Blocked: Watchdog Mode (c)
d) The packet waiting at routing switch R1 port 2 is routed and the network blockage is cleared.
Routing switch R2 port 5 still has data waiting to be sent followed by the end of packet,
therefore packets routed to port 5 will again cause a blockage which will be cleared again in
the same manner until the fault is detected by a higher level protocol.
R1
1
2
3
4
5
6
(d).
1 4
2
3
5
6
R2
Figure 8-20 Destination Node Blocked: Watchdog Mode (d)
8.3.5.2 Stalled source
A source of a SpaceWire packet can stall for some reason and stop sending data part way through
sending a packet. A router will see this situation as an input port which has stalled, no longer sending
data part way through sending a packet although the SpaceWire link is still running. This situation can
occur due to an error in the network or in the node that was providing data.
In blocking allowed mode the network path will be blocked until the source node supplies the end of
packet. Other packets waiting to use the network path will wait indefinitely.
In watchdog timer mode the routers will timeout and the network path will be cleared so other packets
can use the path.
Blocking Allowed
The sequence of events when a source is stalled and Blocking Allowed mode is being used is
illustrated in Figure 8-21 to Figure 8-24.
a) A packet arrives at routing switch port 3 with destination address 4, 5 which will route to
routing switch R2 port 5. Another packet arrives which is destined for routing switch R2 port 4.