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AM5728: PCIe link with SSC

Brian Hammerbacher
Intellectual 285 points
Part Number: AM5728


Hello,

We have a custom carrier board that uses an AM5278 processor that is connector to a FPGA via PCIe.  On the carrier board is a clock generation chip to create a common clock which feeds the AM5278 and the FPGA for PCIe clocking.  

Everything works exactly as expected if we turn off Spread Spectrum clocking, but inorder to meet some EMI levels we need to enable Spread Spectrum.  When we do enable it the AM5278 fails to link to the FPGA.  

Does the AM5278 support spread spectrum clocking with the PLL that runs the PCIe portion?  If so are there settings required to make it function.  

Thank You,
Brian

  • 0
    TI__Mastermind 27890 points

    Hi Brian,

    PCIe SSC isn't supported on this device.

  • 0
    Intellectual 285 points

    Hi, 

    Actually, it seems like i was able to get SSC working just fine.  

    It looks like by default the device is actually setup to use an internal generated clock and not the one fed to the AM5728 pins for PCIe.  

    Once I set CTLR_CORE_SMA_SW_6 (Address 0x4a00 3C14) bits 17:16 to 0x2 putting it in ACSPCIe RX Mode and

    set bits 7 & 8 of CM_CLKMODE_APLL_PCIE (Address 0x4A00 821c) to 1 selecting the ACSPCIE clock.

    My spread spectrum setup started to work perfectly.  Do you mean it does not support outputting a SSC clock.  Because it seems to be accepting one without issue.

  • 0 in reply to Brian Hammerbacher
    TI__Mastermind 27890 points

    Hi Brian,

    In this case "not supported" means that the functionality hasn't been fully tested and characterized by TI so we do not support its use in a product. As you noted, the functionality is there and works, but all responsibility for using it in a product lies with the customer.