Clock domains

Stimulus API

There is a list of ClockDomain stimulation functionalities :

ClockDomain stimulus functions	Description
forkStimulus(period)	Fork a simulation process to generate the clockdomain simulus (clock, reset, softReset, clockEnable signals)
forkSimSpeedPrinter(printPeriod)	Fork a simulation process which will periodicaly print the simulation speed in kcycles per real time second. `printPeriod` is in realtime second
clockToggle()	Toggle the clock signal
fallingEdge()	Clear the clock signal
risingEdge()	Set the clock signal
assertReset()	Set the reset signal to its active level
deassertReset()	Set the reset signal to its inactive level
assertClockEnable()	Set the clockEnable signal to its active level
disassertClockEnable()	Set the clockEnable signal to its active level
assertSoftReset()	Set the softReset signal to its active level
disassertSoftReset()	Set the softReset signal to its active level

Wait API

There is a list of ClockDomain utilities that you can use to wait a given event from it :

ClockDomain wait functions	Description
waitSampling([cyclesCount])	Wait until the ClockDomain made a sampling, (Active clock edge && deassertReset && assertClockEnable)
waitRisingEdge([cyclesCount])	Wait cyclesCount rising edges on the clock, if not cycleCount isn’t specified => 1 cycle, cyclesCount = 0 is legal, not sensitive to reset/softReset/clockEnable
waitFallingEdge([cyclesCount])	Same as waitRisingEdge but for the falling edge
waitActiveEdge([cyclesCount])	Same as waitRisingEdge but for the edge level specified by the ClockDomainConfig
waitRisingEdgeWhere(condition)	As waitRisingEdge, but to exit, the boolean `condition` must be true when the rising edge occure
waitFallingEdgeWhere(condition)	Same as waitRisingEdgeWhere but for the falling edge
waitActiveEdgeWhere(condition)	Same as waitRisingEdgeWhere but for the edge level specified by the ClockDomainConfig

All the functionalities of the wait API can only be called from the inside of a thread, and not from a callback.

Callback API

There is a list of ClockDomain utilities that you can use to wait a given event from it :

ClockDomain callback functions	Description
onNextSampling { callback }	Execute the callback code only once on next the ClockDomain sample (active edge + reset off + clock enable on)
onSamplings { callback }	Execute the callback code each time the ClockDomain sample (active edge + reset off + clock enable on)
onActiveEdges { callback }	Execute the callback code each time the ClockDomain clock do its configured edge
onEdges { callback }	Execute the callback code each time the ClockDomain clock do a rising or falling edge
onRisingEdges { callback }	Execute the callback code each time the ClockDomain clock do a rising edge
onFallingEdges { callback }	Execute the callback code each time the ClockDomain clock do a falling edge

Default ClockDomain

You can access the default ClockDomain of your toplevel by the following way :

//Example of thread forking to generate an reset and then toggeling the clock each 5 units of times.
//dut.clockDomain refer to the implicit clock domain during the component instanciation.
fork{
  dut.clockDomain.assertReset()
  dut.clockDomain.fallingEdge()
  sleep(10)
  while(true){
    dut.clockDomain.clockToggle()
    sleep(5)
  }
}

But you can also directly fork a standard reset/clock process :

dut.clockDomain.forkStimulus(period = 10)

And there is an example of how to wait for a rising edge on the clock :

dut.clockDomain.waitRisingEdge()

New ClockDomain

If you toplevel define some clock and reset inputs which aren’t directly integrated into their clockdomain, you can define their corresponding clockdomain directly in the testbench :

//In the testbench
ClockDomain(dut.io.coreClk, dut.io.coreReset).forkStimulus(10)