Atmel SpaceWire Router SpW-10X User Manual

Ref.:   UoD_SpW-10X_ 

 

Issue:  3.4 

  

 

Date:  11

 

 

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