Atmel SpW-10X Arbitration of packets with different priority, SpaceWire Router, User Manual

SpW-10X	Ref.:	UoD_SpW-10X_
SpaceWire Router		UserManual
	Issue:	3.4
User Manual
	Date:	11th July 2008

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.

Addresses

80 – HIGH Priority

52 – LOW Priority

1 2

80	1
	2	5
	R1
52	3
	4

1

2

R1 5

52 3

4

	Two packets waiting to use port 5				HIGH priority Packet from port 1 is selected
	(Previous port which accessed port 5 = 2)				Packet at port number 3 waits
3				4
		1				1
		2	5			2	5
						R1
		3				3
		4				4
	Packet from port 3 is selected				Packet from port 3 completes

Figure 8-8 Arbitration of two packets with different priority (1)

Preliminary 89