[STM32F3] Increase the supported period range (#1682)

Introducing the prescaler management allows a wider period range support,
from about 65ms before now up to about 32s. We're also introducing
asserts in case the period or prescaler is truncated as the HW registers
are 16 bits large.

Author: LMESTM

libraries/mbed/targets/hal/TARGET_STM/TARGET_STM32F3/TARGET_DISCO_F303VC/objects.h

@@ -99,6 +99,7 @@ struct i2c_s {
 struct pwmout_s {
     PWMName pwm;
     PinName pin;
+    uint32_t prescaler;
     uint32_t period;
     uint32_t pulse;
     uint32_t channel;

libraries/mbed/targets/hal/TARGET_STM/TARGET_STM32F3/TARGET_DISCO_F334C8/objects.h

@@ -99,6 +99,7 @@ struct i2c_s {
 struct pwmout_s {
     PWMName pwm;
     PinName pin;
+    uint32_t prescaler;
     uint32_t period;
     uint32_t pulse;
     uint32_t channel;

libraries/mbed/targets/hal/TARGET_STM/TARGET_STM32F3/TARGET_NUCLEO_F302R8/objects.h

@@ -99,6 +99,7 @@ struct i2c_s {
 struct pwmout_s {
     PWMName pwm;
     PinName pin;
+    uint32_t prescaler;
     uint32_t period;
     uint32_t pulse;
     uint32_t channel;

libraries/mbed/targets/hal/TARGET_STM/TARGET_STM32F3/TARGET_NUCLEO_F303K8/objects.h

@@ -99,6 +99,7 @@ struct i2c_s {
 struct pwmout_s {
     PWMName pwm;
     PinName pin;
+    uint32_t prescaler;
     uint32_t period;
     uint32_t pulse;
     uint32_t channel;

libraries/mbed/targets/hal/TARGET_STM/TARGET_STM32F3/TARGET_NUCLEO_F303RE/objects.h

@@ -99,6 +99,7 @@ struct i2c_s {
 struct pwmout_s {
     PWMName pwm;
     PinName pin;
+    uint32_t prescaler;
     uint32_t period;
     uint32_t pulse;
     uint32_t channel;

libraries/mbed/targets/hal/TARGET_STM/TARGET_STM32F3/TARGET_NUCLEO_F334R8/objects.h

@@ -99,6 +99,7 @@ struct i2c_s {
 struct pwmout_s {
     PWMName pwm;
     PinName pin;
+    uint32_t prescaler;
     uint32_t period;
     uint32_t pulse;
     uint32_t channel;

libraries/mbed/targets/hal/TARGET_STM/TARGET_STM32F3/pwmout_api.c

@@ -96,7 +96,7 @@ void pwmout_write(pwmout_t* obj, float value)
 
     // Configure channels
     sConfig.OCMode       = TIM_OCMODE_PWM1;
-    sConfig.Pulse        = obj->pulse;
+    sConfig.Pulse        = obj->pulse / obj->prescaler;
     sConfig.OCPolarity   = TIM_OCPOLARITY_HIGH;
     sConfig.OCNPolarity  = TIM_OCNPOLARITY_HIGH;
     sConfig.OCFastMode   = TIM_OCFAST_DISABLE;
@@ -161,8 +161,24 @@ void pwmout_period_us(pwmout_t* obj, int us)
     // Update the SystemCoreClock variable
     SystemCoreClockUpdate();
 
-    TimHandle.Init.Period        = us - 1;
-    TimHandle.Init.Prescaler     = (uint16_t)(SystemCoreClock / 1000000) - 1; // 1 us tick
+    /* To make it simple, we use to possible prescaler values which lead to:
+     * pwm unit = 1us, period/pulse can be from 1us to 65535us
+     * or
+     * pwm unit = 500us, period/pulse can be from 500us to ~32.76sec
+     * Be careful that all the channels of a PWM shares the same prescaler
+     */
+    if (us >  0xFFFF) {
+        obj->prescaler = 500;
+    } else {
+        obj->prescaler = 1;
+    }
+    TimHandle.Init.Prescaler     = ((SystemCoreClock / 1000000) * obj->prescaler) - 1;
+
+    MBED_ASSERT(TimHandle.Init.Prescaler < 0xFFFF);
+
+    TimHandle.Init.Period        = (us - 1) / obj->prescaler;
+    MBED_ASSERT(TimHandle.Init.Period < 0xFFFF);
+
     TimHandle.Init.ClockDivision = 0;
     TimHandle.Init.CounterMode   = TIM_COUNTERMODE_UP;