Teledyne LeCroy Summit Z2-16 PCI Express Multi-lane Exerciser User Manual - Manual (Page 31)

Summit Z2-16 Exerciser User Manual Chapter 4: Traffic Generation
Teledyne LeCroy
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Chapter 4: Traffic Generation
A traffic generator can emulate PCI Express™ root complexes and endpoint devices.
Traffic generation can be used to transmit known errors, allowing you to observe how
your device handles faulty link conditions.
After the Summit Z2-16 Exerciser and DUT have been cabled and powered on, you can
test the setup by generating some traffic. The following steps show how to configure the
Exerciser to generate a Link Training sequence.
4.1 Theory of Operation
Overview
The Exerciser offers two mechanisms for implementing traffic generation: scripts, in
which any type of traffic can be defined and executed, and the Generation Options dialog
box, which offers a collection of PCI Express specific behaviors that can be enabled for
automatic generation of traffic.
Using scripts, packets can be transmitted one after another or with certain timing or
event-based pauses between them. This allows the
Exerciser to act as a pattern generator
with PCI Express-specific formatting and transmission rates. However, creating traffic
that emulates real devices with relatively complex protocol behaviors using a simple
pattern generator is quite complicated. Certain behaviors such as ACK policies, and flow
control require concurrent processing. This is where the automated features become
useful.
The Exerciser includes a collection of automated traffic generation circuits that commonly
exist in other PCI Express devices. These circuits include ACK/NAK generation, flow
control management, a Link Training and Status State machine (LTSSM), replay buffers,
and transaction timers. What makes the Exerciser unique and so useful is that each of
these behaviors can be individually modified or disabled. This allows the user to perform
operations that might not otherwise be possible using an off the shelf PCI Express
device. This can be particularly useful when doing compliance or fault recovery testing.
Starting Point
When the Exerciser first powers up, it is at electrical idle on all lanes. The link is not
trained, but the Link Training and Status State Machine (LTSSM) is enabled and waiting
for a command to train the link. To begin communication with a PCI Express device, the
Link training must occur, but first the generation settings must be set. This involves
setting the Link parameters such as link width, polarity inversion, and lane reversal,
through the Generation Options dialog.
Note: Setting the options in the Generation Options dialog has no effect on the
Exerciser behavior until the first script is executed. In fact, each time a script
is executed, these behaviors are reprogrammed to the Exerciser and the
behaviors are modified accordingly.
The Link Connect toolbar button can then be pressed to signal to the LTSSM to initiate
Link training. Alternatively, a script can executed with the Link=L0 command.