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Observer saicgpt
Registered: ‎06-26-2008

PCIE XDMA AXI-streaming and AXI-Lite Master clocks

I have a question on how AXI_ACLK clocks are set up in  PCIE XDMA core v4.1 (vivado 2018.3).  I have the core set up for VC709.  The AXI clock frequency is fixed at 250MHz since the lane width is x8 and maximum link speed is set to 8.0GT/s.


I am using two descriptor bypass C2H interfaces which use axi_aclk running at 250MHz.  I also have AXI Lite Master interface enabled for and the BAR size is set to 1M

The question is whether both C2H axi-streaming and AXI-Lite Master interfaces use same axi_aclk?  Is it possible to use slower version of axi_aclk for AXI-Lite Master interface?  250MHz for the AXI-Lite Master is going to cause problems for us downstream. 

Thanks in advance.

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2 Replies
Xilinx Employee
Xilinx Employee
Registered: ‎07-26-2012

Re: PCIE XDMA AXI-streaming and AXI-Lite Master clocks

Is there a problem with 250 MHz?

The clock should be connected internally in the recent core. PG describes as below:

AXI Bridge for PCIe Gen3 only:
aclk for the S_AXI_CTL interface. Recommended to be
driven by the axi_aclk output. axi_ctl_aclk is a derived
clock from the TXOUTCLK pin from the GT block; it is not
expected to run continuously while axi_ctl_aresetn is

Note: This pin is for legacy use mode only. By default, new IP
generation will have this clock pin internally driven by the IP.
Use axi_aclk pin to clock the design.

(( Page13, PG194))

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Observer saicgpt
Registered: ‎06-26-2008

Re: PCIE XDMA AXI-streaming and AXI-Lite Master clocks

Hello @kurihara 

Thank you for the reply.

There is no problem with 250MHz as such although it's not a continuous clock which is troublesome.  In PCI XDMA core (PG195 instead of PG194), it seems there is only clock avaialble : axi_aclk.  We use that clock for axi-streaming as well as axi-lite master/slave interfaces.  But we have a large mux that generates a lot of FPGA registers using axi-lite master interface and typically would like to run that inteface slower (say 100MHz).  From your answer, it sounds like that is not an option.  

Thank you.

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