diff --git a/docs/articles/verify.md b/docs/articles/verify.md
index 75735c4..42603c1 100644
--- a/docs/articles/verify.md
+++ b/docs/articles/verify.md
@@ -5,7 +5,7 @@
 A verification result records how a device behaved against a stated version of the specification, and it confers no compliance status.
 
 > [!Warning]
-> Verification writes to device registers. Conformance cannot be established without exercising writes, read-only enforcement and event streams, so there is no read-only mode. Some checks leave the device clock and the operation control register in a changed state, and the run assumes a freshly powered device. Avoid verifying a device that is part of a running experiment.
+> Verification writes to device registers. Conformance cannot be established without exercising writes, read-only enforcement and event streams, so there is no read-only mode. Some checks leave the device clock and the operation control register in a changed state, and the run assumes a freshly powered device. An interrupted run can also leave the timestamp register locked until the device is power cycled. Avoid verifying a device that is part of a running experiment.
 
 ## Running a verification
 
diff --git a/src/Harp.Toolkit/Verify/Suites/CoreRegisters/R_CLOCK_CONFIG.cs b/src/Harp.Toolkit/Verify/Suites/CoreRegisters/R_CLOCK_CONFIG.cs
index ccbd64d..232123a 100644
--- a/src/Harp.Toolkit/Verify/Suites/CoreRegisters/R_CLOCK_CONFIG.cs
+++ b/src/Harp.Toolkit/Verify/Suites/CoreRegisters/R_CLOCK_CONFIG.cs
@@ -5,6 +5,11 @@ namespace Harp.Toolkit.Verify.Suites;
 
 internal class R_CLOCK_CONFIG : Suite
 {
+    const uint WriteOffsetSeconds = 10;
+    const string LockNotImplementedMessage = "Setting the lock state had no effect, so the device does not implement the timestamp lock.";
+    const string ClockRoutingMessage = "The device is repeating or generating the synchronization clock, where the effect of CLK_LOCK on writes is unspecified.";
+    const ClockConfigurationFlags ClockRouting = ClockConfigurationFlags.ClockRepeater | ClockConfigurationFlags.ClockGenerator;
+
     public override string Description => "Clock Configuration Register Tests";
 
     [HarpTest(Description = "Validates that ClockConfig register is readable.")]
@@ -13,12 +18,60 @@ public async Task<IResult> IsReadable(VerifyConnection device)
         return await RegisterHelpers.AssertReadableAsync(a => device.ReadByteAsync(a), ClockConfiguration.Address, "ClockConfig");
     }
 
+    [HarpTest(Description = "Validates that the timestamp register accepts a write while CLK_UNLOCK is set.")]
+    public async Task<IResult> UnlockPermitsTimestampWrite(VerifyConnection device)
+    {
+        if (await IsClockRoutingEnabledAsync(device))
+            return new Result<bool>(false, Status.Skipped, ClockRoutingMessage);
+
+        if (!await TrySetClockStateAsync(device, ClockConfigurationFlags.ClockUnlock))
+            return new Result<bool>(false, Status.Skipped, LockNotImplementedMessage);
+
+        var target = await device.ReadTimestampSecondsAsync() + WriteOffsetSeconds;
+        await device.WriteTimestampSecondsAsync(target);
+        var readBack = await device.ReadTimestampSecondsAsync();
+        var elapsedSeconds = (long)readBack - target;
+        return new AssertionResult(
+            elapsedSeconds >= 0 && elapsedSeconds <= 1,
+            x => x
+                ? $"TimestampSeconds accepted {target} while unlocked."
+                : $"Wrote {target} to TimestampSeconds while unlocked and read it back as {readBack}.");
+    }
+
+    [HarpTest(Description = "Validates that the timestamp register refuses a write while CLK_LOCK is set.")]
+    public async Task<IResult> LockRefusesTimestampWrite(VerifyConnection device)
+    {
+        if (await IsClockRoutingEnabledAsync(device))
+            return new Result<bool>(false, Status.Skipped, ClockRoutingMessage);
+
+        try
+        {
+            if (!await TrySetClockStateAsync(device, ClockConfigurationFlags.ClockLock))
+                return new Result<bool>(false, Status.Skipped, LockNotImplementedMessage);
+
+            var target = await device.ReadTimestampSecondsAsync() + WriteOffsetSeconds;
+            var refused = await RegisterHelpers.IsWriteRejectedAsync(
+                device, HarpCommand.WriteUInt32(TimestampSeconds.Address, target));
+            var readBack = await device.ReadTimestampSecondsAsync();
+            return new AssertionResult(
+                readBack < target,
+                x => x
+                    ? "TimestampSeconds kept its value while locked, and the write was " +
+                        (refused ? "answered with an error." : "acknowledged without taking effect.")
+                    : $"Wrote {target} to TimestampSeconds while locked and it took the value, reading back as {readBack}.");
+        }
+        finally
+        {
+            await TrySetClockStateAsync(device, ClockConfigurationFlags.ClockUnlock);
+        }
+    }
+
     [HarpTest(Description = "Reports clock synchronization capability: REP_ABLE (bit 3) and GEN_ABLE (bit 4).")]
     public async Task<IResult> ReportSyncCapability(VerifyConnection device)
     {
-        var value = await device.ReadByteAsync(ClockConfiguration.Address);
-        bool repAble = (value & (1 << 3)) != 0;
-        bool genAble = (value & (1 << 4)) != 0;
+        var value = (ClockConfigurationFlags)await device.ReadByteAsync(ClockConfiguration.Address);
+        bool repAble = value.HasFlag(ClockConfigurationFlags.RepeaterCapability);
+        bool genAble = value.HasFlag(ClockConfigurationFlags.GeneratorCapability);
         StringBuilder sb = new StringBuilder("ClockConfig sync capability:");
         sb.Append("\n");
         sb.Append(repAble ? "Device can repeat clock signal" : "Device cannot repeat clock signal");
@@ -29,4 +82,20 @@ public async Task<IResult> ReportSyncCapability(VerifyConnection device)
             true,
             sb.ToString());
     }
+
+    static async Task<bool> IsClockRoutingEnabledAsync(VerifyConnection device)
+    {
+        var configuration = (ClockConfigurationFlags)await device.ReadByteAsync(ClockConfiguration.Address);
+        return (configuration & ClockRouting) != 0;
+    }
+
+    static async Task<bool> TrySetClockStateAsync(VerifyConnection device, ClockConfigurationFlags state)
+    {
+        var write = HarpCommand.WriteByte(ClockConfiguration.Address, (byte)state);
+        if (await RegisterHelpers.IsWriteRejectedAsync(device, write))
+            return false;
+
+        var configuration = (ClockConfigurationFlags)await device.ReadByteAsync(ClockConfiguration.Address);
+        return (configuration & state) == state;
+    }
 }