AN 755: Implementing JESD204B IP Core System Reference Design with ARM HPS As Control Unit (Baremetal Flow)

ID 683776
Date 12/30/2015
Public
Document Table of Contents

1.3.2. Core PLL

The core PLL generates clocks for the FPGA core fabric. The core PLL uses the device_clk external clock signal as its reference clock to generate two derivative clocks from a single VCO:

  • Link clock—from output C0
  • Frame clock—from output C1
Table 9.  Core PLL Clock Outputs

Clock

Formula

Description

Link Clock

Serial data rate/40

Clocks the JESD204B IP core link layer and the link interface of the transport layer.

Frame Clock

Serial data rate/(10 × F)

Clocks the transport layer, test pattern generators and checkers, and any downstream modules in the FPGA core fabric.

For the frame clock, when F=1 and F=2, the resulting frame clock value can easily exceed the capability of the core PLL to generate and close timing. The top level HDL file (jesd204b_ed.sv) defines the frame clock division factor parameters, F1_FRAMECLK_DIV (for cases with F = 1) and F2_FRAMECLK_DIV (for cases with F = 2). This factor enables the transport layer and test pattern generator to operate at a divided factor of the required frame clock rate by widening the data width accordingly. For this reference design, the F1_FRAMECLK_DIV is set to 4 and F2_FRAMECLK_DIV is set to 2. Based on the default settings of the reference design, the frame clock for a serial data rate of 6.144 Gbps and F = 1 equals to:

(6144/(10 × 1)) / F1_FRAMECLK_DIV = 614.4 / 4 = 153.6 MHz

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