[auton] Added program to control autonomy light.

Author: jtwhit

onboard/auton_light/project.ini

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+[build]
+lang=python
+deps=rover_msgs,rover_common
+executable=True

onboard/auton_light/src/__main__.py

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+import lcm
+from pathlib import Path
+from rover_msgs import AutonState
+
+
+gpio_pin = '397'
+autonomy_on = False
+gpio_path = Path('/sys/class/gpio/gpio{}'.format(gpio_pin))
+export_file = Path('/sys/class/gpio/export')
+unexport_file = Path('/sys/class/gpio/unexport')
+
+
+def export_pin():
+    global gpio_pin, export_file, gpio_path
+    export_file.write_text(gpio_pin)
+    (gpio_path / 'direction').write_text('out')
+
+
+def unexport_pin():
+    global gpio_pin, unexport_file
+    try:
+        unexport_file.write_text(gpio_pin)
+    except OSError:
+        pass
+
+
+def write_gpio(value):
+    global gpio_path
+
+    (gpio_path / 'value').write_text(value)
+
+
+def auton_state_callback(channel, msg):
+    global autonomy_on
+
+    auton_msg = AutonState.decode(msg)
+    if auton_msg.is_auton and not autonomy_on:
+        write_gpio('1')
+        autonomy_on = True
+    elif not auton_msg.is_auton and autonomy_on:
+        write_gpio('0')
+        autonomy_on = False
+
+
+def main():
+    unexport_pin()
+    export_pin()
+    write_gpio('0')
+
+    lc = lcm.LCM()
+    lc.subscribe('/auton', auton_state_callback)
+
+    try:
+        while True:
+            lc.handle()
+    except KeyboardInterrupt:
+        unexport_pin()