@@ -51,6 +51,7 @@
 //synch with win app:
 //all commands must start with 0x64
 #define SetColorToken     0x6422
+#define SetRTCToken       0x6474  //dt
 #define LaunchFileToken   0x6444
 #define PingToken         0x6455
 #define PauseSIDToken     0x6466  //df
 
@@ -52,6 +52,9 @@ FLASHMEM void ServiceSerial(Stream *ThisCmdChannel)
             SendU16(FWMinimalToken);
             return;
          }
+         //left unread, the time bytes would each run as a command of their own: a 0x64 can reset or launch
+         uint32_t RefusedTime;
+         if (inVal == SetRTCToken) GetUInt(&RefusedTime, 4);
          SendU16(FailToken);
          CmdChannel->print("Busy!\n");
          return;
 
@@ -111,6 +111,22 @@ FLASHMEM bool SetColorRef()
    return true;
 }
 
+// Command: 
+// Set the TR's real-time clock, which the TR+'s battery keeps through power-off
+//
+// Workflow:
+// Receive <-- SetRTCToken Token 0x6474
+// Receive <-- UTC time, seconds since 1970 (4 bytes, big endian)
+// Send --> AckToken 0x64CC or FailToken 0x9B7F
+FLASHMEM bool SetRTC()
+{
+   uint32_t SecsSince1970;
+   if (!GetUInt(&SecsSince1970, 4)) return false;
+
+   Teensy3Clock.set(SecsSince1970);
+   return true;
+}
+
 // Command: 
 // Set sub-song number of currently loaded SID
 //
 
@@ -617,6 +617,9 @@ FLASHMEM void ProcessCommand()
 
    if (CurrentIOHandler != IOH_TeensyROM && !ASIDAllowed)
    {
+      //left unread, the time bytes would each run as a command of their own: 'e' resets EEPROM
+      uint32_t RefusedTime;
+      if (TokenVal == SetRTCToken) GetUInt(&RefusedTime, 4);
       SendU16(FailToken);
       CmdChannel->print("Busy!\n");
       return;
@@ -666,6 +669,10 @@ FLASHMEM void ProcessCommand()
          if(SetColorRef()) SendU16(AckToken);
          else SendU16(FailToken);
          break;
+      case SetRTCToken: //Set the real-time clock
+         if(SetRTC()) SendU16(AckToken);
+         else SendU16(FailToken);
+         break;
       case DebugToken: //'dg'Test/debug
          //for (int a=0; a<256; a++) CmdChannel->printf("\n%3d, // %3d   '%c'", ToPETSCII(a), a, a);
          //Printf_dbg("isFab2x: %d\n", isFab2x()); 
 
@@ -118,6 +118,7 @@ A C64 reset the TeensyROM doesn't see (reset detect disabled in Settings) doesn'
 |GetDirectoryToken | 0x64DD  | List directory contents (JSON format - deprecated) |
 |GetDirNDJSONToken | 0x64DE  | List directory contents (NDJSON format) |
 |SetColorToken     | 0x6422  | Set a TR UI color value |
+|SetRTCToken       | 0x6474  | Set the real-time clock |
 |PauseSIDToken     | 0x6466  | Pause SID playback |
 |SetSIDSongToken   | 0x6488  | Set sub-song number of currently loaded SID |
 |SIDSpeedLinToken  | 0x6499  | Set SID playback speed (linear equation) |
@@ -348,6 +349,20 @@ Sets one of the colors in the TR UI. Color is stored in EEPROM and IO space; the
 
 ---
 
+### Set Real-Time Clock
+Sets the TR's real-time clock. The time is UTC; the TR applies its time zone setting when it shows or passes on the time. On a TR+ with a battery, the clock keeps the time through power-off. The menu's clock shows the new time after its next reset.
+
+**Workflow:**
+| Direction | Data |
+|---|---|
+| Receive | `SetRTCToken` — `0x6474` |
+| Receive | UTC time in seconds since 1970-01-01 (4 bytes, big endian) |
+| Send | `AckToken 0x64CC` or `FailToken 0x9B7F` |
+
+**Handler:** `SetRTC()`
+
+---
+
 ### Pause SID
 Pauses/Resumes SID playback by sending an interrupt request to the C64.
 
 
@@ -56,6 +56,7 @@ whatever node appeared beside it.
 | `probe.py` | Which image is running -- main, minimal or silent -- and its build banner. |
 | `ls.py [path] [drive]` | List a directory, to see that a push landed where it was aimed (first 1000 entries). |
 | `reset.py` | Reset the C64 to the menu, and the board out of the minimal image. |
+| `setclock.py [UTC time]` | Set the TR's real-time clock, to this computer's clock or an ISO 8601 UTC time such as `2026-10-16T17:00:00`. Only at the TR menu. |
 | `hostops.py` | Installing and removing a host, and `run_step` -- driving anything that ends in a reboot and reading which of the two shapes came back. Also the phrases a reboot is judged by: `INSTALLED`, `REMOVED` and `FINISHED_NORMALLY`. Shared by the `host*.py` scripts and by `exttest.py`, whose exit status is `finished_normally()`'s answer, so a phrase edited here moves that verdict; and by `test_bounds.py`, which patches its timeouts to test them, and `test_protocol.py`, which pins the phrases against the firmware's own `VmFail::describe()`. |
 | `trlink.py` | The shared library the above are built on. |
 | `protocol.py` | Every value that goes on the wire, named once. |
 
@@ -21,6 +21,7 @@
 POST_FILE = 0x64BB
 DELETE_FILE = 0x64CF
 GET_DIR_NDJSON = 0x64DE
+SET_RTC = 0x6474
 
 # Replies.
 ACK = 0x64CC
@@ -49,6 +50,7 @@
     'PostFileToken': POST_FILE,
     'DeleteFileToken': DELETE_FILE,
     'GetDirNDJSONToken': GET_DIR_NDJSON,
+    'SetRTCToken': SET_RTC,
     'AckToken': ACK,
     'FailToken': FAIL,
     'FWFullToken': FW_FULL,
 
@@ -0,0 +1,27 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: MIT
+"""Set the TR's real-time clock.   setclock.py [UTC time]
+
+The time is UTC, to the second: this computer's clock, or an ISO 8601 time
+such as 2026-10-16T17:00:00. The board refuses it with "Busy!" unless it is
+sitting at its own menu.
+"""
+import datetime, math, sys
+from protocol import SET_RTC, to_board
+from trlink import Link
+
+if len(sys.argv) > 1:
+    when = datetime.datetime.fromisoformat(sys.argv[1])
+    if when.tzinfo is None:
+        when = when.replace(tzinfo=datetime.timezone.utc)
+    when = when.astimezone(datetime.timezone.utc)
+else:
+    when = datetime.datetime.now(datetime.timezone.utc)
+secs = math.floor(when.timestamp())
+if not 0 <= secs < 1 << 32:
+    raise SystemExit(f'{when:%Y-%m-%d %H:%M:%S} UTC is outside 1970-2106, the range four bytes of seconds hold')
+with Link() as tr:
+    tr.drain(0.3)
+    tr.wr(to_board(SET_RTC) + to_board(secs, 4))
+    tr.ack('set clock')
+print('clock set to', when.strftime('%Y-%m-%d %H:%M:%S UTC'))