Altera Arria V Avalon-ST - Manual (Page 230)

packets can be transmitted. If you encounter link training issues, viewing the actual data in hardware
should help you determine the root cause. You can use the following tools to provide hardware visibility:
• SignalTap II Embedded Logic Analyzer
• Third-party PCIe analyzer
You can use SignalTap II Embedded Logic Analyzer to diagnose the LTSSM state transitions that are
occurring on the PIPE interface. The
ltssmstate[4:0]
bus encodes the status of LTSSM. The LTSSM
state machine reflects the Physical Layer’s progress through the link training process. For a complete
description of the states these signals encode, refer to Status, Link Training and Reset Signals. When link
training completes successfully and the link is up, the LTSSM should remain stable in the L0 state. When
link issues occur, you can monitor
ltssmstate[4:0]
to determine the cause.
Related Information
Hard IP Status on page 4-26
Debugging Link Failure in L0 Due To Deassertion of tx_st_ready
There are many reasons that link may stop transmitting data. The following table lists some possible
causes.
Table 17-1: Link Hangs in L0
Possible Causes Symptoms and Root Causes Workarounds and Solutions
Avalon-ST signaling
violates Avalon-ST
protocol
Avalon-ST protocol violations
include the following errors:
• More than one
tx_st_sop
per
tx_st_eop
.
• Two or more
tx_st_eop’s
without a corresponding
tx_
st_sop.
•
rx_st_valid
is not asserted
with
tx_st_sop
or
tx_st_
eop
.
These errors are applicable to
both simulation and hardware.
Add logic to detect situations where
tx_st_
ready
remains deasserted for more than 100
cycles. Set post-triggering conditions to check
for the Avalon-ST signalling of last two TLPs to
verify correct
tx_st_sop
and
tx_st_eop
signalling.
Incorrect payload
size
Determine if the length field of
the last TLP transmitted by End
Point is greater than the InitFC
credit advertised by the link
partner. For simulation, refer to
the log file and simulation
dump. For hardware, use a
third-party logic analyzer trace
to capture PCIe transactions.
If the payload is greater than the initFC credit
advertised, you must either increase the InitFC
of the posted request to be greater than the max
payload size or reduce the payload size of the
requested TLP to be less than the InitFC value.
17-2 Debugging Link Failure in L0 Due To Deassertion of tx_st_ready
2014.12.15
Altera Corporation Debugging
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