Atmel SpaceWire Router SpW-10X 用户手册
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.
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).
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.
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.
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.
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
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