Limitations - 1.0 English

Versal ACAP DMA and Bridge Subsystem for PCI Express Product Guide (PG344)

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Speed Change Related Issue

Repeated speed changes can result in the link not coming up to the intended targeted speed.
A follow-on attempt should bring the link back. In extremely rare scenarios, a full reboot might be required.

Link Autonomous Bandwidth Status (LABS) Bit

As a Root Complex when performing the link width/rate changes, the link width change works as expected. However, the PCIe protocol requires a LABS bit which is not getting set after the link width/rate change.
Note: This is an informational bit and does not impact actual functionality.
Ensure the software / application ignores the LABS bit as this is an informational bit and does not impact functionality.
Note: For any application, Xilinx recommends that you make sure the link is quiesced and no transactions are pending before performing any link rate changes.

AXI Bridge

  1. For this subsystem, the bridge master and bridge slave cannot achieve more than 128 Gb/s.

  2. Bridge will be compliant with all MPS and MRRS settings; however, all traffic initiated from the Bridge will be limited to 256 Bytes (max)
  3. AXI address width is limited to 48 bits.

PCIe Transaction Type

The PCIe® transactions generated are those that are compatible with the AXI4 specification. The following table lists the supported PCIe transaction types.

Table 1. Supported PCIe Transaction Types
MRd32 MRd32
MRd64 MRd64
MWr32 MWr32
MWr64 MWr64
Msg Msg
Cpl Cpl
CplD CplD
Cfg Type0/1 (For Root Port)  

AXI Slave

  • Only supports the INCR burst type. Other types result in the Slave Illegal Burst (SIB) interrupt.
  • No memory type support (AxCACHE)
  • No protection type support (AxPROT)
  • No lock type support (AxLOCK)
  • No non-contiguous byte enable support (WSTRB)

AXI Master

  • Only issues the INCR burst type
  • Only issues the data, non-secure, and unprivileged protection type