AXI Bridge for PCI Express v2.4
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PG055 June 4, 2014
Chapter 3:
Designing with the Core
Link Down Behavior
The normal operation of the AXI Bridge for PCI Express core is dependent on the integrated
block for PCIe establishing and maintaining the point-to-point link with an external device
for PCIe. If the link has been lost, it must be re-established to return to normal operation.
When a Hot Reset is received by the AXI Bridge for PCI Express core, the link goes down and
the PCI Configuration Space must be reconfigured.
Initiated AXI4 write transactions that have not yet completed on the AXI4 bus when the link
goes down have a SLVERR response given and the write data is discarded. Initiated AXI4
read transactions that have not yet completed on the AXI4 bus when the link goes down
have a SLVERR response given, with arbitrary read data returned.
Any MemWr TLPs for PCIe that have been received, but the associated AXI4 write
transaction has not started when the link goes down, are discarded. If the associated AXI4
write transaction is in the process of being transferred, it completes as normal. Any MemRd
TLPs for PCIe that have been received, but have not returned completion TLPs by the time
the link goes down, complete on the AXI4 bus, but do not return completion TLPs on the
PCIe bus.
Root Port
When configured to support Root Port functionality, the AXI Bridge for PCI Express core
fully supports Root Port operation as supported by the underlying block. There are a few
details that need special consideration. The following subsections contain information and
design considerations about Root Port support.
Table 3-7:
Master Bridge Response to Abnormal Conditions
Transfer Type
Abnormal Condition
Bridge Response
Read
DECERR response
MDE interrupt strobe asserted
Completion returned with Unsupported Request status
Write
DECERR response
MDE interrupt strobe asserted
Read
SLVERR response
MSE interrupt strobe asserted
Completion returned with Completer Abort status
Write
SLVERR response
MSE interrupt strobe asserted
Write
Poison bit set in request
MEP interrupt strobe asserted
Data is discarded
Read
DECERR response
MDE interrupt strobe asserted
Completion returned with Unsupported Request status
Write
DECERR response
MDE interrupt strobe asserted