PLL BlackBox and reset controller | SpinalHDL documentation

Let’s imagine you want to define a TopLevel component which instantiates a PLL BlackBox, and create a new clock domain from it which will be used by your core logic. Let’s also imagine that you want to adapt an external asynchronous reset into this core clock domain to a synchronous reset source.

The following imports will be used in code examples on this page:

import spinal.core._
import spinal.lib._

The PLL BlackBox definition

This is how to define the PLL BlackBox:

class PLL extends BlackBox{
  val io = new Bundle{
    val clkIn    = in Bool
    val clkOut   = out Bool
    val isLocked = out Bool
  }

  noIoPrefix()
}

This will correspond to the following VHDL component:

component PLL is
  port(
    clkIn    : in std_logic;
    clkOut   : out std_logic;
    isLocked : out std_logic
  );
end component;

TopLevel definition

This is how to define your TopLevel which instantiates the PLL, creates the new ClockDomain, and also adapts the asynchronous reset input to a synchronous reset:

class TopLevel extends Component{
  val io = new Bundle {
    val aReset    = in Bool
    val clk100Mhz = in Bool
    val result    = out UInt(4 bits)
  }

  // Create an Area to manage all clocks and reset things
  val clkCtrl = new Area {
    //Instanciate and drive the PLL
    val pll = new PLL
    pll.io.clkIn := io.clk100Mhz

    //Create a new clock domain named 'core'
    val coreClockDomain = ClockDomain.internal(
      name = "core",
      frequency = FixedFrequency(200 MHz)  // This frequency specification can be used
    )                                      // by coreClockDomain users to do some calculations

    //Drive clock and reset signals of the coreClockDomain previously created
    coreClockDomain.clock := pll.io.clkOut
    coreClockDomain.reset := ResetCtrl.asyncAssertSyncDeassert(
      input = io.aReset || ! pll.io.isLocked,
      clockDomain = coreClockDomain
    )
  }

  //Create a ClockingArea which will be under the effect of the clkCtrl.coreClockDomain
  val core = new ClockingArea(clkCtrl.coreClockDomain){
    //Do your stuff which use coreClockDomain here
    val counter = Reg(UInt(4 bits)) init(0)
    counter := counter + 1
    io.result := counter
  }
}

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