pwm: add calls for getting PWM max and min period

Resolves #176

Signed-off-by: Thomas Ingleby <thomas.c.ingleby@intel.com>

api/mraa/pwm.h

@@ -186,6 +186,20 @@ mraa_result_t mraa_pwm_config_ms(mraa_pwm_context dev, int period, float duty);
  */
 mraa_result_t mraa_pwm_config_percent(mraa_pwm_context dev, int period, float duty);
 
+/**
+ * Get the maximum pwm period in us
+ *
+ * @return max pwm in us
+ */
+int mraa_pwm_get_max_period();
+
+/**
+ * Get the minimum pwm period in us
+ *
+ * @return min pwm in us
+ */
+int mraa_pwm_get_min_period();
+
 #ifdef __cplusplus
 }
 #endif

api/mraa/pwm.hpp

@@ -204,6 +204,26 @@ class Pwm
     {
         return mraa_pwm_config_percent(m_pwm, period, duty);
     }
+    /**
+     * Get the maximum pwm period in us
+     *
+     * @return max pwm in us
+     */
+    int
+    max_period()
+    {
+        return mraa_pwm_get_max_period();
+    }
+    /**
+     * Get the minimum pwm period in us
+     *
+     * @return min pwm in us
+     */
+    int
+    min_period()
+    {
+        return mraa_pwm_get_min_period();
+    }
 
   private:
     mraa_pwm_context m_pwm;