Altera Arria V Hard IP for PCI Express User Manual
Page 275
Chapter 18: Debugging
18–5
Link Hangs in L0 Due To Deassertion of tx_st_ready
December 2013
Altera Corporation
Arria V Hard IP for PCI Express
User Guide
f
For more information about link training, refer to the “Link Training and Status State
Machine (LTSSM) Descriptions” section of
Flow control credit
overflows
Determine if the credit field associated
with the current TLP type in the
tx_cred
bus is less than the requested
credit value. When insufficient credits
are available, the core waits for the link
partner to release the correct credit
type. Sufficient credits may be
unavailable if the link partner
increments credits more than expected,
creating a situation where the Arria V
Hard IP for PCI Express IP Core credit
calculation is out-of-sink with its link
partner.
Add logic to detect conditions where the
tx_st_ready
signal remains deasserted for more
than 100 cycles. Set post-triggering conditions to
check the value of the
tx_cred*
and
tx_st_*
interfaces. Add a FIFO status signal to determine if
the TXFIFO is full.
Malformed TLP is
transmitted
Refer to the log file to find the last good
packet transmitted on the link. Correlate
this packet with TLP sent on Avalon-ST
interface. Determine if the last TLP sent
has any of the following errors:
■
The actual payload sent does not
match the length field.
■
The byte enable signals violate rules
for byte enables as specified in the
.
■
The format and type fields are
incorrectly specified.
■
TD field is asserted, indicating the
presence of a TLP digest (ECRC),
but the ECRC dword is not present at
the end of TLP.
■
The payload crosses a 4KByte
boundary.
Revise the Application Layer logic to correct the
error condition.
Insufficient Posted credits
released by Root Port
If a Memory Write TLP is transmitted
with a payload greater than the
maximum payload size, the Root Port
may release an incorrect posted data
credit to the End Point in simulation. As
a result, the End Point does not have
enough credits to send additional
Memory Write Requests.
Make sure Application Layer sends Memory Write
Requests with a payload less than or equal the
value specified by the maximum payload size.
Missing completion packets
or dropped packets
The RX Completion TLP might cause
the RX FIFO to overflow. Make sure that
the total outstanding read data of all
pending Memory Read Requests is
smaller than the allocated completion
credits in RX buffer.
You must ensure that the data for all outstanding
read requests does not exceed the completion
credits in the RX buffer.
Table 18–2. Link Hangs in L0 (Part 2 of 2)
Possible Causes
Symptoms and Root Causes
Workarounds and Solutions