AN 661: Implementing Fractional PLL Reconfiguration with Altera PLL and Altera PLL Reconfig IP Cores

ID 683640
Date 10/14/2019
Public
Document Table of Contents

1.1.1.5. Reconfiguring Fractional PLL Settings with Avalon-MM Interface

You can dynamically reconfigure fPLLs with the Avalon®-MM interface. To perform dynamic reconfiguration, follow these steps:

  1. Through an Avalon write operation, write to the mode register a value of 0 or 1 at the startup of the Altera PLL Reconfig IP core. The mode register determines whether the Altera PLL Reconfig IP core operates in waitrequest or polling mode.
  2. Specify the element and its new value through an Avalon write operation.
    For more information about the address for each reconfigurable element, refer to Fractional PLL Dynamic Reconfiguration Registers and Settings, and Dynamic Phase Shift Counter and cnt_select (Dynamic_Phase_Shift[20:16]) Bit Setting tables.
  3. Repeat Step 2 for all the reconfigurable elements (N, M, C counters, MFRAC value, and others) that you want to change.
  4. Through an Avalon write operation, write either 0 or 1 to the start register. Writing to the start register triggers the dynamic reconfiguration, the dynamic phase shift, or both:
    • If you set the mode register to 0 (waitrequest mode) in Step 1, the Altera PLL Reconfig IP core asserts the mgmt_waitrequest signal until after the reconfiguration. You can only perform another Avalon read or write operation after the Altera PLL Reconfig IP core deasserts the mgmt_waitrequest signal.
    • If you set the mode register to 1 (polling mode) in Step 1, the Altera PLL Reconfig IP core writes 0 (busy) to the status register. You can poll bit 0 of the status register periodically by performing Avalon read operations to ensure that the reconfiguration is complete. The Altera PLL Reconfig IP core ignores any new reconfiguration instructions (Avalon write operations) until a value of 1 has been read from the status register.
    Lock the fractional PLL to the reference clock before you perform the dynamic reconfiguration or the dynamic phase shifting.