IDT Tsi578, User Manual

Page: 200 / 527

8. Performance > Congestion Detection and Management 200
Tsi578 User Manual
June 6, 2016
Integrated Device Technology
www.idt.com
Figure 43: Congestion Example
The Packet Receipt Rate in the chart indicates how quickly packets can enter and leave the queue.
Essentially, this represents the packet line rate. A system with smaller packets increases this receipt rate
while a system with predominantly large packages decreases this rate.
The chart also shows the Congestion Period Counter tick and the Leak Rate Timer tick. These ticks
occur based on their programmed values (see
“RapidIO Port x Transmitter Output Queue Depth
Threshold Register” on page 350 ). In this example, the DEPTH bit is programmed to four in the
“RapidIO Port x Transmitter Output Queue Depth Threshold Register” on page 350 .
Also shown is the Congestion Period Count value (see “RapidIO Port x Transmitter Output Queue
Depth Threshold Register” on page 350 ) and the Congestion Counter value (see “RapidIO Port x
Transmitter Output Queue Congestion Status Register” on page 352 ).
In this example, the value of the Congestion Threshold has been set to eight (see “RapidIO Port x
Transmitter Output Queue Congestion Status Register” on page 352 ). When the Congestion Counter
equals the value in the Congestion Threshold, the OUTB_DEPTH interrupt is asserted (see “RapidIO
Port x Interrupt Status Register” on page 326 ). When the OUTB_DEPTH interrupt is asserted, a
port-write packet can be generated which causes an in-band notification of the condition that can be
routed to any host in the system.
1
2
3
4
Packets in Egress Queue
5
6
7
8
Packet Receipt Rate
Leak Rate Timer tick
(DEPTH field set to 4)
Congestion Period Counter tick
Congestion Period Count value
Congestion Counter value
0
0
0 0
1
1 1 1 0 1
Interrupt OUTB_DEPTH
(Congestion Threshold set to 8)
2 3 4 5 6 7 8 9 10
2 3