cli: Support reading and previewing a custom channel.

README.md

@@ -33,6 +33,9 @@ openmv --port /dev/ttyACM0 --quiet
 
 # Debug mode (verbose logging)
 openmv --port /dev/ttyACM0 --debug
+
+# Preview a custom data channel
+openmv --port /dev/ttyACM0 --channel ticks
 ```
 
 ### Options
@@ -47,6 +50,7 @@ openmv --port /dev/ttyACM0 --debug
 | `--timeout SEC` | 1.0 | Protocol timeout in seconds |
 | `--baudrate N` | 921600 | Serial baudrate |
 | `--firmware FILE` | None | Firmware ELF file for profiler symbol resolution |
+| `--channel NAME` | None | Custom data channel to poll and print |
 | `--quiet` | False | Suppress script output text |
 | `--debug` | False | Enable debug logging |
 
@@ -108,6 +112,46 @@ with Camera('/dev/ttyACM0') as camera:
             print(text, end='')
 ```
 
+### Custom Channels
+
+Custom channels allow bidirectional data exchange between the camera and host.
+
+**Camera-side script (MicroPython):**
+
+```python
+import time
+import protocol
+
+class TicksChannel:
+    def size(self):
+        return 10
+
+    def read(self, offset, size):
+        return f'{time.ticks_ms():010d}'
+
+    def poll(self):
+        return True
+
+protocol.register(name='ticks', backend=TicksChannel())
+```
+
+**Host-side (Python):**
+
+```python
+from openmv import Camera
+
+with Camera('/dev/ttyACM0') as camera:
+    camera.exec(script)
+
+    while True:
+        # Check if channel has data
+        if camera.has_channel('ticks'):
+            size = camera.channel_size('ticks')
+            if size > 0:
+                data = camera.channel_read('ticks', size)
+                print(f"Ticks: {data.decode()}")
+```
+
 ## API Reference
 
 Full API documentation: [docs/api.md](https://github.com/openmv/openmv-python/blob/master/docs/api.md)

src/openmv/cli.py

@@ -35,7 +35,25 @@
 
 # Default test script for csi-based cameras
 test_script = """
-import csi, image, time
+import time
+import protocol
+import csi
+import image
+
+class TicksChannel:
+    def __init__(self):
+        pass
+
+    def size(self):
+        return 10
+
+    def read(self, offset, size):
+        return f'{time.ticks_ms():010d}'
+
+    def poll(self):
+        return True
+
+ch1 = protocol.register(name='ticks', backend=TicksChannel())
 
 csi0 = csi.CSI()
 csi0.reset()
@@ -145,6 +163,10 @@ def main():
                         action='store_true',
                         help='Suppress script output text')
 
+    parser.add_argument('--channel',
+                        action='store', default=None,
+                        help='Custom channel to poll and read')
+
     args = parser.parse_args()
 
     # Register signal handlers for clean exit
@@ -249,6 +271,13 @@ def main():
                     if text := camera.read_stdout():
                         print(text, end='')
 
+                # Read custom channel
+                if args.channel and status and status.get(args.channel):
+                    if size := camera.channel_size(args.channel):
+                        data = camera.channel_read(args.channel, size=size)
+                        preview = data[:10] if len(data) > 10 else data
+                        logging.info(f"[{args.channel}] ({size} bytes) {preview}")
+
                 # Read frame data
                 if frame := camera.read_frame():
                     fps = fps_clock.get_fps()