Atmel SpaceWire Router SpW-10X - Manual (Page 89)

Ref.: UoD_SpW-10X_
UserManual
Issue: 3.4
SpW-10X
SpaceWire Router
User Manual Date: 11 th
July 2008
Preliminary
89
8.3.2.3 Arbitration of packets with different priority (1)
In the Figure 8-8 arbitration of packets with different priority is illustrated. Only router ports 1-5 are
shown for clarity.
At stage one input ports 1 and 3 have packets with logical addresses 80 and 52 respectively, which
are both to be routed to output port 5. Logical address 80 is high priority and 52 low priority.
At stage two the previous input port selected by output port 5 was input port 2 but since input port 1
has a packet waiting with logical address 80 which is high priority, input port 1 will be selected first and
the packet with logical address 80 transferred to output port 5.
At stage three the high priority packet with logical address from input port 1 has been transferred and
the remaining low priority packet from input port 3 is selected by the router to be transferred to output
port 5.
R1
2
5
1
3 52
4
80
R1
2
5
1
3 52
4
Two packets waiting to use port 5
(Previous port which accessed port 5 = 2)
HIGH priority Packet from port 1 is selected
Packet at port number 3 waits
R1
2
5
1
3
4
Packet from port 3 is selected
R1
2
5
1
3
4
Packet from port 3 completes
1 2
3 4
Addresses
80 – HIGH Priority
52 – LOW Priority
Figure 8-8 Arbitration of two packets with different priority (1)