GTS AXI Streaming Intel® FPGA IP for PCI Express* User Guide

ID 813754
Date 1/24/2025
Public

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4.1.1. Reference Clock

There is one local and one regional reference clock pin in each GTS bank to drive the TX PLL and CDR in PMA, and the System PLL in the bank. For x4 mode, the TX PLL, CDR and System PLL can be driven from either the local or the regional reference clock pin in the same GTS bank, or driven from other banks through the regional reference clock networks. For x8 mode, the System PLL must be driven from the local reference clock pin of the GTS bank where the x8 controller is located; the TX PLL and CDR are driven from the regional reference clock pin in the same bank or other banks.

The reference clock to the System PLL must be available and stable before device configuration starts. For common reference clock architectures, if the reference clock is not guaranteed to be available before device configuration starts, derive the reference clock from an independent and free-running local clock source. The following figure shows the reference clock to drive the system PLL is from an independent local oscillator. It does not share the reference clock from the host which drives the TX PLL and CDR in the PMA.

Figure 10. System PLL Reference Clock from a Free Running Oscillator in a Common Clock Architecture

For independent reference clock architectures, you can use the local reference clock to drive the TX PLL, CDR, and the system PLL. The local reference clock must be active and stable before device configuration starts.

Figure 11. System PLL Reference Clock from a Free Running Oscillator in an Independent Clock Architecture
Once the reference clock for the system PLL is up; it must be stable; it must be present throughout the device operation and must not go down. If you are not able to adhere to these requirements, you must reconfigure the device. After the temporary loss of the system PLL reference clock, you may observe that the first try of device reconfiguration fails. If that happens, you should try to reconfigure the device a second time.
Note: Refer to the Clock Architecture and Implementing the GTS System PLL Clocks Intel FPGA IP sections in the GTS Transceiver PHY User Guide .