STM32: fix HRTIM pwm init and corner case (#31)

* STM32: fix HRTIM pwm corner cases (0-100%) in read function

* STM32: fix HRTIM pwm init with default values

* STM32: add helper fun to manage pwmout obj period

Author: leonardocavagnis

Diff for: targets/TARGET_STM/pwmout_api.c

@@ -53,6 +53,8 @@ static hrtim_t hrtim_timer;
 static HRTIM_HandleTypeDef HrtimHandle;
 static HRTIM_CompareCfgTypeDef sConfig_compare;
 static HRTIM_TimeBaseCfgTypeDef sConfig_time_base;
+
+static void _pwmout_obj_period_us(pwmout_t *obj, int us);
 #endif
 
 /* Convert STM32 Cube HAL channel to LL channel */
@@ -142,9 +144,9 @@ static void _pwmout_init_direct(pwmout_t *obj, const PinMap *pinmap)
         pin_function(pinmap->pin, pinmap->function);
         pin_mode(pinmap->pin, PullNone);
 
-        obj->period = 0;
-        obj->pulse = 0;
-        obj->prescaler = 0;
+        // Initialize obj with default values (period 550Hz, duty 0%)
+        _pwmout_obj_period_us(obj, 18000);
+        obj->pulse = (uint32_t)((float)obj->period * 1.0 + 0.5);
 
         // Initialize the HRTIM structure
         HrtimHandle.Instance = HRTIM1;
@@ -444,6 +446,15 @@ float pwmout_read(pwmout_t *obj)
     if (obj->period > 0) {
         value = (float)(obj->pulse) / (float)(obj->period);
     }
+
+    if (obj->pwm == PWM_I) {
+        if (value <= (float)0.0) {
+            value = 1.0;
+        } else if (value >= (float)1.0) {
+            value = 0.0;
+        }
+    }
+
     return ((value > (float)1.0) ? (float)(1.0) : (value));
 }
 
@@ -464,24 +475,7 @@ void pwmout_period_us(pwmout_t *obj, int us)
     if (obj->pwm == PWM_I) {
         float dc = pwmout_read(obj);
 
-        uint32_t frequency;
-        uint32_t clocksource = __HAL_RCC_GET_HRTIM1_SOURCE();
-        switch (clocksource) {
-            case RCC_HRTIM1CLK_TIMCLK:
-                frequency = HAL_RCC_GetHCLKFreq();
-                break;
-            case RCC_HRTIM1CLK_CPUCLK:
-                frequency = HAL_RCC_GetSysClockFreq();
-                break;
-        }
-
-        /* conversion from us to clock tick */
-        obj->period = us * (frequency / 1000000) / 4;
-        obj->prescaler = HRTIM_PRESCALERRATIO_DIV4;
-
-        if (obj->period > 0xFFDFU) {
-            obj->period = 0xFFDFU;
-        }
+        _pwmout_obj_period_us(obj, us);
 
         sConfig_time_base.Mode = HRTIM_MODE_CONTINUOUS;
         sConfig_time_base.Period = obj->period;
@@ -602,4 +596,27 @@ const PinMap *pwmout_pinmap()
     return PinMap_PWM;
 }
 
+#if defined(HRTIM1)
+void _pwmout_obj_period_us(pwmout_t *obj, int us) {
+    uint32_t frequency;
+    uint32_t clocksource = __HAL_RCC_GET_HRTIM1_SOURCE();
+    switch (clocksource) {
+        case RCC_HRTIM1CLK_TIMCLK:
+            frequency = HAL_RCC_GetHCLKFreq();
+            break;
+        case RCC_HRTIM1CLK_CPUCLK:
+            frequency = HAL_RCC_GetSysClockFreq();
+            break;
+    }
+
+    /* conversion from us to clock tick */
+    obj->period = us * (frequency / 1000000) / 4;
+    obj->prescaler = HRTIM_PRESCALERRATIO_DIV4;
+
+    if (obj->period > 0xFFDFU) {
+        obj->period = 0xFFDFU;
+    }
+}
+#endif
+
 #endif