Xilinx LogiCORE IP Ethernet AVB Endpoint v2.4 User Manual page 62

Chapter 6: Ethernet AVB Endpoint Transmission
X-Ref Target - Figure 6-4
hiLimit
Figure 6-4
•
•
•
•
62
increasing
credit
idleSlope
credit=0
when no frames
are waiting
0
loLimit
number of AV
queued frames
1
0
transmitting
AV frame
TRUE
FALSE
transmitting
Legacy frame
TRUE
FALSE
Figure 6-4: Credit-based Shaper Operation
illustrates the key features of the credit based algorithm, which are:
The Tx Arbiter will schedule queued transmission from the
algorithm is in credit (greater or equal to 0).
If there is less than 0 credit (not shown in
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.
www.xilinx.com
sendSlope
conflicting legacy traffic present, so queued AV frame is not
transmitted until conflicting legacy frame has been transmitted
Figure
credits withdrawn
when no frames
are waiting
"Tx AV Traffic I/F"
6-4, but the credit can sink below 0),
Ethernet AVB Endpoint User Guide
UG492 September 21, 2010
increasing
time
if the