@@ -1,15 +1,21 @@
+MAX_PWM_NUM = 5
 PWM_IF_PREFIX = "/sys/class/leds/pwm"
 PWM_IF_MAX = "max_brightness"
 PWM_IF = "brightness"
 
 MAX_PWM_LEVEL = 255
 
-#sprintf(path, "%s%d/%s", PWM_IF_PREFIX, pin, PWM_IF_MAX);
-
 def _max_value(pin):
-    return 256
+    with open("%s%d/%s" % (PWM_IF_PREFIX, pin, PWM_IF_MAX)) as f:
+        return int(f.read())
 
 def analog_write(pin, value):
+    if (pin < 0 or pin > MAX_PWM_NUM or
+        value < 0 or value > MAX_PWM_LEVEL):
+        raise ValueError(
+            "pin must be between 0 and %s. value must be between 0 and %s" % (
+                MAX_PWM_NUM, MAX_PWM_LEVEL))
+
     map_level = (_max_value(pin) * value) / MAX_PWM_LEVEL
     with open("%s%d/%s" % (PWM_IF_PREFIX, pin, PWM_IF), 'w+') as f:
         f.write("%d\n" % map_level)