feat(rpi-gpio): support GPIO inputs and add module README

src/python/otsim/rpi_gpio/README.md

@@ -0,0 +1,37 @@
+# Raspberry Pi GPIO Module
+
+This OT-sim module leverages the [RPi.GPIO](https://pypi.org/project/RPi.GPIO/)
+Python module to associate OT-sim tags with input and output pins.
+
+Please note the following about this module:
+
+1. This module will only work when OT-sim is run on a Raspberry Pi. To avoid
+long compilation times, the suggested way to do so is to run OT-sim on a
+Raspberry Pi using the OT-sim Docker image, which is a multi-architecture build.
+1. Each input and output is used to setup the corresponding GPIO channel,
+defined by the `pin` assignment.
+1. This module only supports boolean inputs and outputs (`PWM` is not
+supported).
+1. This module only subscribes to `update` messages from the OT-sim message bus,
+and only publishes `status` messages to the OT-sim message bus. GPIO inputs are
+mapped to input tags, and output tags are mapped to GPIO outputs.
+1. On exit, `GPIO.cleanup()` is called, which will set all used channels back to
+inputs with no pull up/down. This may cause anything physically connected to the
+channels to be affected.
+
+## Example Configuration
+
+```
+<rpi-gpio name="rpi-hil" mode="board"> <!-- mode can be "board" or "bcm" -->
+  <period>1</period> <!-- how often, in seconds, to read GPIO inputs; defaults to 5 -->
+  <output pin="11">
+    <tag>led-11</tag>
+  </output>
+  <output pin="13">
+    <tag>relay-1-3</tag>
+  </output>
+  <input pin="17">
+    <tag>switch-17</tag>
+  </input>
+</rpi-gpio>
+```

src/python/otsim/rpi_gpio/rpi_gpio.py

@@ -1,24 +1,31 @@
 from __future__ import annotations
 
-import json, logging, signal, sys, threading, typing
+import logging, signal, sys, threading, time, typing
 
 import otsim.msgbus.envelope as envelope
 import xml.etree.ElementTree as ET
 
-from otsim.msgbus.envelope   import Envelope
+from otsim.msgbus.envelope   import Envelope, Point
+from otsim.msgbus.pusher     import Pusher
 from otsim.msgbus.subscriber import Subscriber
 
 import RPi.GPIO as GPIO
 
 
 class RPiGPIO:
   def __init__(self: RPiGPIO, pub: str, pull: str, el: ET.Element):
+    # map pin numbers --> tag
+    self.inputs: typing.Dict[int, str] = {}
     # map tags --> pin number
     self.outputs: typing.Dict[str, int] = {}
 
+    self.monitoring = True
+
     self.name = el.get('name', default='ot-sim-rpi-gpio')
     mode      = el.get('mode', default='BOARD')
 
+    GPIO.setwarnings(False)
+
     if mode.upper() == 'BOARD':
       GPIO.setmode(GPIO.BOARD)
     elif mode.upper() == 'BCM':
@@ -27,8 +34,20 @@ def __init__(self: RPiGPIO, pub: str, pull: str, el: ET.Element):
       print(f"unknown GPIO mode '{mode}' - defaulting to 'BOARD' mode")
       GPIO.setmode(GPIO.BOARD)
 
-    pub_endpoint    = el.findtext('pub-endpoint', default=pub)
+    pub_endpoint  = el.findtext('pub-endpoint', default=pub)
+    pull_endpoint = el.findtext('pull-endpoint', default=pull)
+
     self.subscriber = Subscriber(pub_endpoint)
+    self.pusher     = Pusher(pull_endpoint)
+
+    self.period = float(el.findtext('period', default=5))
+
+    for o in el.findall('input'):
+      pin = int(o.get('pin'))
+      tag = o.findtext('tag')
+
+      self.inputs[pin] = tag
+      GPIO.setup(pin, GPIO.IN)
 
     for o in el.findall('output'):
       pin = int(o.get('pin'))
@@ -43,12 +62,35 @@ def __init__(self: RPiGPIO, pub: str, pull: str, el: ET.Element):
   def start(self: RPiGPIO):
     self.subscriber.start('RUNTIME')
 
+    # run GPIO monitor in a thread
+    self.monitor_thread = threading.Thread(target=self.monitor, daemon=True).start()
+
 
   def stop(self: RPiGPIO):
+    self.monitoring = False
+    self.monitor_thread.join(self.period)
+
     GPIO.cleanup()
     self.subscriber.stop()
 
 
+  def monitor(self: RPiGPIO):
+    if len(self.inputs) == 0:
+      return
+
+    while self.monitoring:
+      points: typing.List[Point] = []
+
+      for pin, tag in self.inputs.items():
+        val = GPIO.input(pin)
+        points.append({'tag': tag, 'value': float(val), 'ts': 0})
+
+      env = envelope.new_status_envelope(self.name, {'measurements': points})
+      self.pusher.push('RUNTIME', env)
+
+      time.sleep(self.period)
+
+
   def handle_msgbus_update(self: RPiGPIO, env: Envelope):
     update = envelope.update_from_envelope(env)