When clocks diverge too much, packet sources might schedule packets into the past, resulting in error

[adamgeorge309]

When clocks diverge too much, it results in this error:

Cannot schedule message (inet::ClockEvent)ProductionTimer to the past, t=0.0469998 -- in module (inet::queueing::ActivePacketSource) ClockDriftShowcase.source2.app[0].source (id=208), at t=0.047s, event #142502

For reproduction: run OutOfBandSynchronizationRandomDrift config

NED:

//
// SPDX-License-Identifier: LGPL-3.0-or-later
//

package inet.showcases.tsn.timesynchronization.clockdrift;

import inet.networks.base.WiredNetworkBase;
import inet.node.ethernet.Eth1G;
import inet.node.ethernet.EthernetSwitch;
import inet.node.inet.StandardHost;

network ClockDriftShowcase extends WiredNetworkBase
{
submodules:
source1: StandardHost {
@display("p=300,100");
}
source2: StandardHost {
@display("p=300,300");
}
switch1: EthernetSwitch {
@display("p=500,200");
}
switch2: EthernetSwitch {
@display("p=700,200");
}
sink1: StandardHost {
@display("p=900,100");
}
sink2: StandardHost {
@display("p=900,300");
}
connections:
switch1.ethg++ <--> Eth1G <--> switch2.ethg++;
source1.ethg++ <--> Eth1G <--> switch1.ethg++;
source2.ethg++ <--> Eth1G <--> switch1.ethg++;
switch2.ethg++ <--> Eth1G <--> sink1.ethg++;
switch2.ethg++ <--> Eth1G <--> sink2.ethg++;
}

INI:

[General]
network = ClockDriftShowcase
sim-time-limit = 0.1s

..ethernet.typename = "EthernetLayer"

**.hasGlobalArp = true

.source.numApps = 1
.source.app[*].typename = "UdpSourceApp"
.source.app[0].source.packetLength = 800B
.source.app[0].source.productionInterval = 20us
.source.app[0].io.destPort = 1000

*.source1.app[0].io.destAddress = "sink1"
*.source1.app[0].source.packetNameFormat = "source1-%c"

*.source2.app[0].io.destAddress = "sink2"
*.source2.app[0].source.initialProductionOffset = 10us
*.source2.app[0].source.packetNameFormat = "source2-%c"

.sink.numApps = 1
.sink.app[*].typename = "UdpSinkApp"
.sink.app[0].io.localPort = 1000

..eth[].typename = "LayeredEthernetInterface"
..eth[].bitrate = 1Gbps
*.switch1.eth[0].macLayer.queue.typename = "GatingPriorityQueue"
*.switch1.eth[0].macLayer.queue.numQueues = 2
.switch1.eth[0].macLayer.queue.classifier.typename = "ContentBasedClassifier"
.switch1.eth[0].macLayer.queue.classifier.packetFilters = ["source1", "source2"]
.switch1.eth[0].macLayer.queue.queue[].typename = "DropTailQueue"
.switch1.eth[0].macLayer.queue.gate[].initiallyOpen = false
.switch1.eth[0].macLayer.queue.gate[].durations = [10us, 10us]
*.switch1.eth[0].macLayer.queue.gate[1].offset = 10us

[Config RandomClockDriftRate]
description = "Clocks with random drift rate"

.source.clock.typename = "OscillatorBasedClock"
.source.clock.oscillator.typename = "RandomDriftOscillator"
*.source1.clock.oscillator.driftRateChange = intuniform(-500ppm, 500ppm)
*.source2.clock.oscillator.driftRateChange = intuniform(-400ppm, 400ppm)
*.source1.clock.oscillator.changeInterval = 0.1ms
*.source2.clock.oscillator.changeInterval = 0.1ms
.source.app[0].source.clockModule = "^.^.clock"

*.switch1.clock.typename = "OscillatorBasedClock"
*.switch1.clock.oscillator.typename = "RandomDriftOscillator"
*.switch1.clock.oscillator.driftRateChange = intuniform(-300ppm, 300ppm)
*.switch1.clock.oscillator.changeInterval = 0.1ms
.switch1.eth[0].macLayer.queue.gate[].clockModule = "^.^.^.^.clock"

[Config OutOfBandSynchronizationRandomDrift]
description = "Clocks are periodically synchronized out-of-band, without a real protocol. Clocks use random drift oscillators."
extends = RandomClockDriftRate

.source.clock.typename = "SettableClock"
.source.clock.defaultOverdueClockEventHandlingMode = "execute"

.source.numApps = 2
.source.app[1].typename = "SimpleClockSynchronizer"
.source.app[1].masterClockModule = "^.^.switch1.clock"
.source.app[1].slaveClockModule = "^.clock"
.source.app[1].synchronizationInterval = 500us
.source.app[1].synchronizationClockTimeError = uniform(-10ns, 10ns)