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Viewing Offline Performance Summary
11
In this example, 4092B (1023 DW) packets of data are being sent in the downstream direction and
the link partner is updating credits in increments of 4096B. In the following screen, a steep decline in
the blue line clearly indicates the situation that FC credit is being updated at higher rate than the
rate at which data is being posted. The blue line represents the computed UpdateFC_P regulating
against the red line representing the corresponding Memory Write packets in the trace.
The UpdateFC_P Flow Control credit level is reduced by Memory Write packets coming from the root
occurred in the trace. As displayed in the above graph, the Maximum is near the beginning of the
trace and the Flow Control credit level continuously drops down and reaches zero on the right side of
the trace.
This too many credits difference may indicate problem in the credit update behavior of the DUT.
Example-2
In the following screen, when memory completion data (Memory CplD) is being sent, the
UpdateFC_Cpl performance parameter computes and displays minimum, maximum, as well as
average flow control credit levels for Completions data. The blue and orange Pyramid Up chart line
represents Memory CplD and UpdateFC_Cpl respectively. The UpdateFC_Cpl credit starts from an
initial counter value and keeps on updating its credit limit till all the packets are sent and received.
Keysight U4301 PCIe Gen3 Analyzer User's Guide
177
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