Atmel SpaceWire Router SpW-10X - Manual (Page 88)

Ref.: UoD_SpW-10X_
UserManual
Issue: 3.4
SpW-10X
SpaceWire Router
User Manual Date: 11 th
July 2008
Preliminary
88
8.3.2.2 Arbitration of packets with matching priority (2)
In the Figure 8-7 another example of arbitrating between packets with the same priority is illustrated.
Again only router ports 1-5 are shown for clarity.
At stage one input ports 1 and 3 have packets to be routed to output port 5. The previous input port to
use output port 5 was input port 3 therefore the next input port to be selected by output port 5 will be
input port 1 (assuming input ports 6, 7, 8, 9, 10 and 0 are not requesting to use the port).
At stage two the router selects the packet at input port 1 and a packet is routed to output port 5. Input
port 3 waits until the complete packet has been transferred. While the packet from input port 1 is
being transferred to output port 5 another packet arrives at input port 2 to be routed to output port 5.
At stage three the packet from input port 1 has been forwarded and the packet from input port 2 is
selected by the router to be routed through output port 5. Input port two is selected before input port 3
as it is the next input port to be considered by the routing control logic after input port 1.
At stage four p the complete packet has been transferred from input port 2. Now input port 3 is able to
transfer its packet to output port 5.
R1
2
5
1
3 5
4
5
R1
2
5
1
3 5
4
Two packets waiting to use port 5
(Previous port which accessed port 5 = 3)
Packet from port 1 is selected
Packet arrives on port 2
R1
2
5
1
3
4
Packet from port 1 completes
Packet from port 2 is selected
Packet from port 3 waits
R1
2
5
1
3
4
Packet from port 2 completes
Packet from port 3 is selected
1 2
3 4
5
5
Figure 8-7 Arbitration of three packets with matching priority