Add example for can with watchdog timer handling

examples/can_simple.py

@@ -1,21 +1,29 @@
 """
 Minimal example for controlling an ODrive via the CANSimple protocol.
 
-Puts the ODrive into closed loop control mode, sends a velocity setpoint of 1.0
-and then prints the encoder feedback.
+Puts the ODrive into closed loop control mode, sends periodic sinusoidal velocity
+setpoints, and asynchronously prints the encoder feedback.
 
 Assumes that the ODrive is already configured for velocity control.
 
+If the watchdog is enabled on the ODrive, it is fed implicitly by the continuous
+velocity setpoint message and the motor will stop when the script is terminated.
+The heartbeat interval should be shorter than the watchdog timeout to ensure
+timely confirmation of the axis entering closed loop control mode without 
+triggering the watchdog.
+
 See https://docs.odriverobotics.com/v/latest/manual/can-protocol.html for protocol
 documentation.
 """
 
 import can
+import math
+import time
 import struct
 
 node_id = 0 # must match `<odrv>.axis0.config.can.node_id`. The default is 0.
 
-bus = can.interface.Bus("can0", bustype="socketcan")
+bus = can.interface.Bus("can0", interface="socketcan")
 
 # Flush CAN RX buffer so there are no more old pending messages
 while not (bus.recv(timeout=0) is None): pass
@@ -34,15 +42,21 @@
         if state == 8: # 8: AxisState.CLOSED_LOOP_CONTROL
             break
 
-# Set velocity to 1.0 turns/s
-bus.send(can.Message(
-    arbitration_id=(node_id << 5 | 0x0d), # 0x0d: Set_Input_Vel
-    data=struct.pack('<ff', 1.0, 0.0), # 1.0: velocity, 0.0: torque feedforward
-    is_extended_id=False
-))
-
-# Print encoder feedback
-for msg in bus:
+# Handler for incoming CAN messages to print encoder feedback
+def on_rx_message(msg: can.Message):
     if msg.arbitration_id == (node_id << 5 | 0x09): # 0x09: Get_Encoder_Estimates
         pos, vel = struct.unpack('<ff', bytes(msg.data))
         print(f"pos: {pos:.3f} [turns], vel: {vel:.3f} [turns/s]")
+
+# Control ODrive while notifier object exist
+with can.Notifier(bus, [on_rx_message]):
+    while True:
+        velocity_setpoint = math.sin(2 * math.pi * 0.5 * time.monotonic()) # turns / s
+
+        # Update velocity and reset watchdog timer 
+        bus.send(can.Message(
+            arbitration_id=(node_id << 5 | 0x0d), # 0x0d: Set_Input_Vel
+            data=struct.pack('<ff', velocity_setpoint, 0.0), # 0.0: torque feedforward
+            is_extended_id=False
+        ))
+        time.sleep(0.1)