Chapter 6: Ethernet AVB Endpoint Transmission

increasing

 

 

 

credit

 

idleSlope

sendSlope

 

 

 

hiLimit

 

 

 

 

 

 

credit=0

credits withdrawn

 

 

when no frames

 

when no frames

 

are waiting

 

 

are waiting

 

 

 

 

0

 

 

 

 

increasing

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

time

loLimit

conflicting legacy traffic present, so queued AV frame is not

number of AV transmitted until conflicting legacy frame has been transmitted queued frames

1

0

transmitting

AV frame

TRUE

FALSE

transmitting

Legacy frame

TRUE

FALSE

Figure 6-4:Credit-based Shaper Operation

Figure 6-4illustrates the key features of the credit based algorithm, which are:

The Tx Arbiter will schedule queued transmission from the “Tx AV Traffic I/F” if the algorithm is in credit (greater or equal to 0).

If there is less than 0 credit (not shown in Figure 6-4, but the credit can sink below 0), then the Tx Arbiter will not allow AV traffic to be transmitted; legacy traffic, if queued, will be scheduled instead.

When no AV traffic is queued, any positive credit will be lost and the credit is reset to 0.

When AV traffic is queued, and until the time at which the Tx Arbiter is able to schedule it (while waiting for an in-progress legacy frame to complete transmission), credit can be gained at a rate defined by the idleSlope.

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Ethernet AVB Endpoint User Guide

 

 

UG492 July 23, 2010

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Xilinx UG492 manual 4Credit-based Shaper Operation