diff --git a/os/hal/include/pwm.h b/os/hal/include/pwm.h
index e63478ca3..7181054e4 100644
--- a/os/hal/include/pwm.h
+++ b/os/hal/include/pwm.h
@@ -57,13 +57,16 @@ typedef enum {
 } pwmstate_t;
 
 /**
- * @brief PWM logic mode.
+ * @brief   Type of a structure representing a PWM driver.
  */
-typedef enum {
-  PWM_OUTPUT_DISABLED = 0,          /**< Output not driven, callback only.  */
-  PWM_OUTPUT_ACTIVE_HIGH = 1,       /**< Idle is logic level 0.             */
-  PWM_OUTPUT_ACTIVE_LOW = 2         /**< Idle is logic level 1.             */
-} pwmmode_t;
+typedef struct PWMDriver PWMDriver;
+
+/**
+ * @brief   PWM notification callback type.
+ *
+ * @param[in] pwmp      pointer to a @p PWMDriver object
+ */
+typedef void (*pwmcallback_t)(PWMDriver *pwmp);
 
 #include "pwm_lld.h"
 
@@ -72,12 +75,86 @@ typedef enum {
 /*===========================================================================*/
 
 /**
- * @brief   Enables a PWM channel.
- * @details Programs (or reprograms) a PWM channel.
- * @note    This function has to be invoked from a lock zone.
+ * @brief   Converts from fraction to pulse width.
+ * @note    Be careful with rounding errors, this is integer math not magic.
+ *          You can specify tenths of thousandth but make sure you have the
+ *          proper hardware resolution by carefully choosing the clock source
+ *          and prescaler settings, see @p PWM_COMPUTE_PSC.
  *
  * @param[in] pwmp      pointer to a @p PWMDriver object
- * @param[in] channel   PWM channel identifier
+ * @param[in] denominator denominator of the fraction
+ * @param[in] numerator numerator of the fraction
+ * @return              The pulse width to be passed to @p pwmEnableChannel().
+ *
+ * @api
+ */
+#define PWM_FRACTION_TO_WIDTH(pwmp, denominator, numerator)                 \
+  ((uint16_t)((((uint32_t)(pwmp)->period) *                                 \
+               (uint32_t)(numerator)) / (uint32_t)(denominator)))
+
+/**
+ * @brief   Converts from degrees to pulse width.
+ * @note    Be careful with rounding errors, this is integer math not magic.
+ *          You can specify hundredths of degrees but make sure you have the
+ *          proper hardware resolution by carefully choosing the clock source
+ *          and prescaler settings, see @p PWM_COMPUTE_PSC.
+ *
+ * @param[in] pwmp      pointer to a @p PWMDriver object
+ * @param[in] degrees   degrees as an integer between 0 and 36000
+ * @return              The pulse width to be passed to @p pwmEnableChannel().
+ *
+ * @api
+ */
+#define PWM_DEGREES_TO_WIDTH(pwmp, degrees)                                 \
+  PWM_FRACTION_TO_WIDTH(pwmp, 36000, degrees)
+
+/**
+ * @brief   Converts from percentage to pulse width.
+ * @note    Be careful with rounding errors, this is integer math not magic.
+ *          You can specify tenths of thousandth but make sure you have the
+ *          proper hardware resolution by carefully choosing the clock source
+ *          and prescaler settings, see @p PWM_COMPUTE_PSC.
+ *
+ * @param[in] pwmp      pointer to a @p PWMDriver object
+ * @param[in] percentage percentage as an integer between 0 and 10000
+ * @return              The pulse width to be passed to @p pwmEnableChannel().
+ *
+ * @api
+ */
+#define PWM_PERCENTAGE_TO_WIDTH(pwmp, percentage)                           \
+  PWM_FRACTION_TO_WIDTH(pwmp, 10000, percentage)
+
+/**
+ * @brief   Changes the period the PWM peripheral.
+ * @details This function changes the period of a PWM unit that has already
+ *          been activated using @p pwmStart().
+ * @pre     The PWM unit must have been activated using @p pwmStart().
+ * @post    The PWM unit period is changed to the new value.
+ * @post    Any active channel is disabled by this function and must be
+ *          activated explicitly using @p pwmEnableChannel().
+ * @note    Depending on the hardware implementation this function has
+ *          effect starting on the next cycle (recommended implementation)
+ *          or immediately (fallback implementation).
+ *
+ * @param[in] pwmp      pointer to a @p PWMDriver object
+ *
+ * @iclass
+ */
+#define pwmChangePeriodI(pwmp, period) {                                    \
+  (pwmp)->period = (period);                                                \
+  pwm_lld_change_period(pwmp, period);                                      \
+}
+
+/**
+ * @brief   Enables a PWM channel.
+ * @pre     The PWM unit must have been activated using @p pwmStart().
+ * @post    The channel is active using the specified configuration.
+ * @note    Depending on the hardware implementation this function has
+ *          effect starting on the next cycle (recommended implementation)
+ *          or immediately (fallback implementation).
+ *
+ * @param[in] pwmp      pointer to a @p PWMDriver object
+ * @param[in] channel   PWM channel identifier (0...PWM_CHANNELS-1)
  * @param[in] width     PWM pulse width as clock pulses number
  *
  * @iclass
@@ -86,13 +163,16 @@ typedef enum {
   pwm_lld_enable_channel(pwmp, channel, width)
 
 /**
- * @brief Disables a PWM channel.
- * @details The channel is disabled and its output line returned to the
+ * @brief   Disables a PWM channel.
+ * @pre     The PWM unit must have been activated using @p pwmStart().
+ * @post    The channel is disabled and its output line returned to the
  *          idle state.
- * @note    This function has to be invoked from a lock zone.
+ * @note    Depending on the hardware implementation this function has
+ *          effect starting on the next cycle (recommended implementation)
+ *          or immediately (fallback implementation).
  *
  * @param[in] pwmp      pointer to a @p PWMDriver object
- * @param[in] channel   PWM channel identifier
+ * @param[in] channel   PWM channel identifier (0...PWM_CHANNELS-1)
  *
  * @iclass
  */
@@ -110,6 +190,7 @@ extern "C" {
   void pwmObjectInit(PWMDriver *pwmp);
   void pwmStart(PWMDriver *pwmp, const PWMConfig *config);
   void pwmStop(PWMDriver *pwmp);
+  void pwmChangePeriod(PWMDriver *pwmp, pwmcnt_t period);
   void pwmEnableChannel(PWMDriver *pwmp,
                         pwmchannel_t channel,
                         pwmcnt_t width);
diff --git a/os/hal/platforms/STM32/gpt_lld.c b/os/hal/platforms/STM32/gpt_lld.c
index ffbfe475c..8419cad68 100644
--- a/os/hal/platforms/STM32/gpt_lld.c
+++ b/os/hal/platforms/STM32/gpt_lld.c
@@ -325,6 +325,7 @@ void gpt_lld_stop(GPTDriver *gptp) {
   if (gptp->state == GPT_READY) {
     gptp->tim->CR1  = 0;                    /* Timer disabled.              */
     gptp->tim->DIER = 0;                    /* All IRQs disabled.           */
+    gptp->tim->SR   = 0;                    /* Clear eventual pending IRQs. */
 
 #if STM32_GPT_USE_TIM1
     if (&GPTD1 == gptp) {
diff --git a/os/hal/platforms/STM32/pwm_lld.c b/os/hal/platforms/STM32/pwm_lld.c
index eaf83bd90..6b05b66aa 100644
--- a/os/hal/platforms/STM32/pwm_lld.c
+++ b/os/hal/platforms/STM32/pwm_lld.c
@@ -289,12 +289,15 @@ void pwm_lld_init(void) {
 
 /**
  * @brief   Configures and activates the PWM peripheral.
+ * @note    Starting a driver that is already in the @p PWM_READY state
+ *          disables all the active channels.
  *
  * @param[in] pwmp      pointer to a @p PWMDriver object
  *
  * @notapi
  */
 void pwm_lld_start(PWMDriver *pwmp) {
+  uint32_t clock, psc;
   uint16_t ccer;
 
   /* Reset channels.*/
@@ -311,6 +314,7 @@ void pwm_lld_start(PWMDriver *pwmp) {
                        CORTEX_PRIORITY_MASK(STM32_PWM_TIM1_IRQ_PRIORITY));
       NVICEnableVector(TIM1_CC_IRQn,
                        CORTEX_PRIORITY_MASK(STM32_PWM_TIM1_IRQ_PRIORITY));
+      clock = STM32_TIMCLK2;
     }
 #endif
 #if STM32_PWM_USE_TIM2
@@ -320,6 +324,7 @@ void pwm_lld_start(PWMDriver *pwmp) {
       RCC->APB1RSTR = 0;
       NVICEnableVector(TIM2_IRQn,
                        CORTEX_PRIORITY_MASK(STM32_PWM_TIM2_IRQ_PRIORITY));
+      clock = STM32_TIMCLK1;
     }
 #endif
 #if STM32_PWM_USE_TIM3
@@ -329,6 +334,7 @@ void pwm_lld_start(PWMDriver *pwmp) {
       RCC->APB1RSTR = 0;
       NVICEnableVector(TIM3_IRQn,
                        CORTEX_PRIORITY_MASK(STM32_PWM_TIM3_IRQ_PRIORITY));
+      clock = STM32_TIMCLK1;
     }
 #endif
 #if STM32_PWM_USE_TIM4
@@ -338,6 +344,7 @@ void pwm_lld_start(PWMDriver *pwmp) {
       RCC->APB1RSTR = 0;
       NVICEnableVector(TIM4_IRQn,
                        CORTEX_PRIORITY_MASK(STM32_PWM_TIM4_IRQ_PRIORITY));
+      clock = STM32_TIMCLK1;
     }
 #endif
 
@@ -348,6 +355,7 @@ void pwm_lld_start(PWMDriver *pwmp) {
       RCC->APB1RSTR = 0;
       NVICEnableVector(TIM5_IRQn,
                        CORTEX_PRIORITY_MASK(STM32_PWM_TIM5_IRQ_PRIORITY));
+      clock = STM32_TIMCLK1;
     }
 #endif
 
@@ -364,21 +372,26 @@ void pwm_lld_start(PWMDriver *pwmp) {
   }
   else {
     /* Driver re-configuration scenario, it must be stopped first.*/
-    /* Really required ?????????? */
-    pwmp->tim->CR1  = 0;                    /* Timer stopped.               */
-    pwmp->tim->CR2  = 0;                    /* Timer stopped.               */
-    pwmp->tim->SMCR = 0;                    /* Slave mode disabled.         */
+    pwmp->enabled_channels = 0;             /* All channels disabled.       */
+    pwmp->tim->CR1  = 0;                    /* Timer disabled.              */
+    pwmp->tim->DIER = 0;                    /* All IRQs disabled.           */
+    pwmp->tim->SR   = 0;                    /* Clear eventual pending IRQs. */
     pwmp->tim->CCR1 = 0;                    /* Comparator 1 disabled.       */
     pwmp->tim->CCR2 = 0;                    /* Comparator 2 disabled.       */
     pwmp->tim->CCR3 = 0;                    /* Comparator 3 disabled.       */
     pwmp->tim->CCR4 = 0;                    /* Comparator 4 disabled.       */
-    pwmp->tim->CNT  = 0;
+    pwmp->tim->CNT  = 0;                    /* Counter reset to zero.       */
   }
 
   /* Timer configuration.*/
+  psc = (clock / pwmp->config->frequency) - 1;
+  chDbgAssert((psc <= 0xFFFF) &&
+              ((psc + 1) * pwmp->config->frequency) == clock,
+              "pwm_lld_start(), #1", "invalid frequency");
+  pwmp->tim->PSC  = (uint16_t)psc;
+  pwmp->tim->ARR  = (uint16_t)(pwmp->period - 1);
   pwmp->tim->CR2  = pwmp->config->cr2;
-  pwmp->tim->PSC  = pwmp->config->psc;
-  pwmp->tim->ARR  = pwmp->config->arr;
+
   /* Output enables and polarities setup.*/
   ccer = 0;
   switch (pwmp->config->channels[0].mode) {
@@ -434,17 +447,9 @@ void pwm_lld_stop(PWMDriver *pwmp) {
   /* If in ready state then disables the PWM clock.*/
   if (pwmp->state == PWM_READY) {
     pwmp->enabled_channels = 0;             /* All channels disabled.       */
-    pwmp->tim->CR1   = 0;
-    pwmp->tim->CR2   = 0;
-    pwmp->tim->CCER  = 0;                   /* Outputs disabled.            */
-    pwmp->tim->CCR1  = 0;                   /* Comparator 1 disabled.       */
-    pwmp->tim->CCR2  = 0;                   /* Comparator 2 disabled.       */
-    pwmp->tim->CCR3  = 0;                   /* Comparator 3 disabled.       */
-    pwmp->tim->CCR4  = 0;                   /* Comparator 4 disabled.       */
-    pwmp->tim->BDTR  = 0;
-    pwmp->tim->DIER  = 0;
-    pwmp->tim->SR    = 0;
-    pwmp->tim->EGR   = TIM_EGR_UG;          /* Update event.                */
+    pwmp->tim->CR1  = 0;                    /* Timer disabled.              */
+    pwmp->tim->DIER = 0;                    /* All IRQs disabled.           */
+    pwmp->tim->SR   = 0;                    /* Clear eventual pending IRQs. */
 
 #if STM32_PWM_USE_TIM1
     if (&PWMD1 == pwmp) {
@@ -480,8 +485,39 @@ void pwm_lld_stop(PWMDriver *pwmp) {
   }
 }
 
+/**
+ * @brief   Changes the period the PWM peripheral.
+ * @details This function changes the period of a PWM unit that has already
+ *          been activated using @p pwmStart().
+ * @pre     The PWM unit must have been activated using @p pwmStart().
+ * @post    The PWM unit period is changed to the new value.
+ * @post    Any active channel is disabled by this function and must be
+ *          activated explicitly using @p pwmEnableChannel().
+ * @note    The function has effect at the next cycle start.
+ *
+ * @param[in] pwmp      pointer to a @p PWMDriver object
+ *
+ * @api
+ */
+void pwm_lld_change_period(PWMDriver *pwmp, pwmcnt_t period) {
+
+  pwmp->enabled_channels = 0;           /* All channels disabled.           */
+  pwmp->tim->DIER &= ~(TIM_DIER_CC1IE |
+                       TIM_DIER_CC2IE |
+                       TIM_DIER_CC3IE |
+                       TIM_DIER_CC4IE); /* Channels sources disabled.       */
+  pwmp->tim->SR    = ~(TIM_SR_CC1IF |
+                       TIM_SR_CC1IF |
+                       TIM_SR_CC1IF |
+                       TIM_SR_CC1IF);   /* Clears eventual pending IRQs.    */
+  pwmp->tim->ARR   = (uint16_t)(period - 1);
+}
+
 /**
  * @brief   Enables a PWM channel.
+ * @pre     The PWM unit must have been activated using @p pwmStart().
+ * @post    The channel is active using the specified configuration.
+ * @note    The function has effect at the next cycle start.
  *
  * @param[in] pwmp      pointer to a @p PWMDriver object
  * @param[in] channel   PWM channel identifier (0...PWM_CHANNELS-1)
@@ -508,8 +544,10 @@ void pwm_lld_enable_channel(PWMDriver *pwmp,
 
 /**
  * @brief   Disables a PWM channel.
- * @details The channel is disabled and its output line returned to the
+ * @pre     The PWM unit must have been activated using @p pwmStart().
+ * @post    The channel is disabled and its output line returned to the
  *          idle state.
+ * @note    The function has effect at the next cycle start.
  *
  * @param[in] pwmp      pointer to a @p PWMDriver object
  * @param[in] channel   PWM channel identifier (0...PWM_CHANNELS-1)
diff --git a/os/hal/platforms/STM32/pwm_lld.h b/os/hal/platforms/STM32/pwm_lld.h
index 8c15a3c6f..d8e1754c9 100644
--- a/os/hal/platforms/STM32/pwm_lld.h
+++ b/os/hal/platforms/STM32/pwm_lld.h
@@ -169,16 +169,13 @@ typedef uint8_t pwmchannel_t;
 typedef uint16_t pwmcnt_t;
 
 /**
- * @brief   Type of a structure representing an PWM driver.
+ * @brief PWM logic mode.
  */
-typedef struct PWMDriver PWMDriver;
-
-/**
- * @brief   PWM notification callback type.
- *
- * @param[in] pwmp      pointer to a @p PWMDriver object
- */
-typedef void (*pwmcallback_t)(PWMDriver *pwmp);
+typedef enum {
+  PWM_OUTPUT_DISABLED = 0,          /**< Output not driven, callback only.  */
+  PWM_OUTPUT_ACTIVE_HIGH = 1,       /**< Idle is logic level 0.             */
+  PWM_OUTPUT_ACTIVE_LOW = 2         /**< Idle is logic level 1.             */
+} pwmmode_t;
 
 /**
  * @brief   PWM driver channel configuration structure.
@@ -201,6 +198,18 @@ typedef struct {
  * @brief   PWM driver configuration structure.
  */
 typedef struct {
+  /**
+   * @brief   Timer clock in Hz.
+   * @note    The low level can use assertions in order to catch invalid
+   *          frequency specifications.
+   */
+  uint32_t                  frequency;
+  /**
+   * @brief   PWM period in ticks.
+   * @note    The low level can use assertions in order to catch invalid
+   *          period specifications.
+   */
+  pwmcnt_t                  period;
   /**
    * @brief Periodic callback pointer.
    * @note  This callback is invoked on PWM counter reset. If set to
@@ -212,14 +221,6 @@ typedef struct {
    */
   PWMChannelConfig          channels[PWM_CHANNELS];
   /* End of the mandatory fields.*/
-  /**
-   * @brief TIM PSC (pre-scaler) register initialization data.
-   */
-  uint16_t                  psc;
-  /**
-   * @brief TIM ARR (auto-reload) register initialization data.
-   */
-  uint16_t                  arr;
   /**
    * @brief TIM CR2 register initialization data.
    * @note  The value of this field should normally be equal to zero.
@@ -239,6 +240,10 @@ struct PWMDriver {
    * @brief Current driver configuration data.
    */
   const PWMConfig           *config;
+  /**
+   * @brief   Current PWM period in ticks.
+   */
+  pwmcnt_t                  period;
 #if defined(PWM_DRIVER_EXT_FIELDS)
   PWM_DRIVER_EXT_FIELDS
 #endif
@@ -257,90 +262,6 @@ struct PWMDriver {
 /* Driver macros.                                                            */
 /*===========================================================================*/
 
-/**
- * @brief   PWM clock prescaler initialization utility.
- * @note    The real clock value is rounded to the lower valid value, please
- *          make sure that the source clock frequency is a multiple of the
- *          requested PWM clock frequency.
- * @note    The calculated value must fit into an unsigned 16 bits integer.
- *
- * @param[in] clksrc    clock source frequency, depending on the target timer
- *                      cell it can be one of:
- *                      - STM32_TIMCLK1
- *                      - STM32_TIMCLK2
- *                      .
- *                      Please refer to the STM32 HAL driver documentation
- *                      and/or the STM32 Reference Manual for the right clock
- *                      source.
- * @param[in] pwmclk    PWM clock frequency in cycles
- * @return              The value to be stored in the @p psc field of the
- *                      @p PWMConfig structure.
- */
-#define PWM_COMPUTE_PSC(clksrc, pwmclk)                                     \
-  ((uint16_t)(((clksrc) / (pwmclk)) - 1))
-
-/**
- * @brief   PWM cycle period initialization utility.
- * @note    The calculated value must fit into an unsigned 16 bits integer.
- *
- * @param[in] pwmclk    PWM clock frequency in cycles
- * @param[in] pwmperiod PWM cycle period in nanoseconds
- * @return              The value to be stored in the @p arr field of the
- *                      @p PWMConfig structure.
- */
-#define PWM_COMPUTE_ARR(pwmclk, pwmperiod)                                  \
-  ((uint16_t)(((pwmclk) / (1000000000 / (pwmperiod))) - 1))
-
-/**
- * @brief   Converts from fraction to pulse width.
- * @note    Be careful with rounding errors, this is integer math not magic.
- *          You can specify tenths of thousandth but make sure you have the
- *          proper hardware resolution by carefully choosing the clock source
- *          and prescaler settings, see @p PWM_COMPUTE_PSC.
- *
- * @param[in] pwmp      pointer to a @p PWMDriver object
- * @param[in] numerator numerator of the fraction
- * @param[in] denominator percentage as an integer between 0 and numerator
- * @return              The pulse width to be passed to @p pwmEnableChannel().
- *
- * @api
- */
-#define PWM_FRACTION_TO_WIDTH(pwmp, numerator, denominator)                 \
-  ((uint16_t)((((uint32_t)(pwmp)->config->arr + 1UL) *                      \
-               (uint32_t)(denominator)) / (uint32_t)(numerator)))
-
-/**
- * @brief   Converts from degrees to pulse width.
- * @note    Be careful with rounding errors, this is integer math not magic.
- *          You can specify hundredths of degrees but make sure you have the
- *          proper hardware resolution by carefully choosing the clock source
- *          and prescaler settings, see @p PWM_COMPUTE_PSC.
- *
- * @param[in] pwmp      pointer to a @p PWMDriver object
- * @param[in] degrees   degrees as an integer between 0 and 36000
- * @return              The pulse width to be passed to @p pwmEnableChannel().
- *
- * @api
- */
-#define PWM_DEGREES_TO_WIDTH(pwmp, degrees)                                 \
-  PWM_FRACTION_TO_WIDTH(pwmp, 36000, degrees)
-
-/**
- * @brief   Converts from percentage to pulse width.
- * @note    Be careful with rounding errors, this is integer math not magic.
- *          You can specify tenths of thousandth but make sure you have the
- *          proper hardware resolution by carefully choosing the clock source
- *          and prescaler settings, see @p PWM_COMPUTE_PSC.
- *
- * @param[in] pwmp      pointer to a @p PWMDriver object
- * @param[in] percentage percentage as an integer between 0 and 10000
- * @return              The pulse width to be passed to @p pwmEnableChannel().
- *
- * @api
- */
-#define PWM_PERCENTAGE_TO_WIDTH(pwmp, percentage)                           \
-  PWM_FRACTION_TO_WIDTH(pwmp, 10000, percentage)
-
 /*===========================================================================*/
 /* External declarations.                                                    */
 /*===========================================================================*/
@@ -371,6 +292,7 @@ extern "C" {
   void pwm_lld_init(void);
   void pwm_lld_start(PWMDriver *pwmp);
   void pwm_lld_stop(PWMDriver *pwmp);
+  void pwm_lld_change_period(PWMDriver *pwmp, pwmcnt_t period);
   void pwm_lld_enable_channel(PWMDriver *pwmp,
                               pwmchannel_t channel,
                               pwmcnt_t width);
diff --git a/os/hal/src/pwm.c b/os/hal/src/pwm.c
index e510ba180..eaa49bc56 100644
--- a/os/hal/src/pwm.c
+++ b/os/hal/src/pwm.c
@@ -77,6 +77,8 @@ void pwmObjectInit(PWMDriver *pwmp) {
 
 /**
  * @brief   Configures and activates the PWM peripheral.
+ * @note    Starting a driver that is already in the @p PWM_READY state
+ *          disables all the active channels.
  *
  * @param[in] pwmp      pointer to a @p PWMDriver object
  * @param[in] config    pointer to a @p PWMConfig object
@@ -91,6 +93,7 @@ void pwmStart(PWMDriver *pwmp, const PWMConfig *config) {
   chDbgAssert((pwmp->state == PWM_STOP) || (pwmp->state == PWM_READY),
               "pwmStart(), #1", "invalid state");
   pwmp->config = config;
+  pwmp->period = config->period;
   pwm_lld_start(pwmp);
   pwmp->state = PWM_READY;
   chSysUnlock();
@@ -115,9 +118,41 @@ void pwmStop(PWMDriver *pwmp) {
   chSysUnlock();
 }
 
+/**
+ * @brief   Changes the period the PWM peripheral.
+ * @details This function changes the period of a PWM unit that has already
+ *          been activated using @p pwmStart().
+ * @pre     The PWM unit must have been activated using @p pwmStart().
+ * @post    The PWM unit period is changed to the new value.
+ * @post    Any active channel is disabled by this function and must be
+ *          activated explicitly using @p pwmEnableChannel().
+ * @note    Depending on the hardware implementation this function has
+ *          effect starting on the next cycle (recommended implementation)
+ *          or immediately (fallback implementation).
+ *
+ * @param[in] pwmp      pointer to a @p PWMDriver object
+ *
+ * @api
+ */
+void pwmChangePeriod(PWMDriver *pwmp, pwmcnt_t period) {
+
+  chDbgCheck(pwmp != NULL, "pwmChangePeriod");
+
+  chSysLock();
+  chDbgAssert(pwmp->state == PWM_READY,
+              "pwmChangePeriod(), #1", "invalid state");
+  pwmp->period = period;
+  pwm_lld_change_period(pwmp, period);
+  chSysUnlock();
+}
+
 /**
  * @brief   Enables a PWM channel.
- * @details Programs (or reprograms) a PWM channel.
+ * @pre     The PWM unit must have been activated using @p pwmStart().
+ * @post    The channel is active using the specified configuration.
+ * @note    Depending on the hardware implementation this function has
+ *          effect starting on the next cycle (recommended implementation)
+ *          or immediately (fallback implementation).
  *
  * @param[in] pwmp      pointer to a @p PWMDriver object
  * @param[in] channel   PWM channel identifier (0...PWM_CHANNELS-1)
@@ -141,8 +176,12 @@ void pwmEnableChannel(PWMDriver *pwmp,
 
 /**
  * @brief   Disables a PWM channel.
- * @details The channel is disabled and its output line returned to the
+ * @pre     The PWM unit must have been activated using @p pwmStart().
+ * @post    The channel is disabled and its output line returned to the
  *          idle state.
+ * @note    Depending on the hardware implementation this function has
+ *          effect starting on the next cycle (recommended implementation)
+ *          or immediately (fallback implementation).
  *
  * @param[in] pwmp      pointer to a @p PWMDriver object
  * @param[in] channel   PWM channel identifier (0...PWM_CHANNELS-1)
diff --git a/os/hal/templates/pwm_lld.c b/os/hal/templates/pwm_lld.c
index 507ba1294..295b0dcb4 100644
--- a/os/hal/templates/pwm_lld.c
+++ b/os/hal/templates/pwm_lld.c
@@ -87,23 +87,32 @@ void pwm_lld_stop(PWMDriver *pwmp) {
 }
 
 /**
- * @brief   Determines whatever the PWM channel is already enabled.
+ * @brief   Changes the period the PWM peripheral.
+ * @details This function changes the period of a PWM unit that has already
+ *          been activated using @p pwmStart().
+ * @pre     The PWM unit must have been activated using @p pwmStart().
+ * @post    The PWM unit period is changed to the new value.
+ * @post    Any active channel is disabled by this function and must be
+ *          activated explicitly using @p pwmEnableChannel().
+ * @note    Depending on the hardware implementation this function has
+ *          effect starting on the next cycle (recommended implementation)
+ *          or immediately (fallback implementation).
  *
- * @param[in] pwmp      pointer to the @p PWMDriver object
- * @param[in] channel   PWM channel identifier
- * @return              The PWM channel status.
- * @retval FALSE        the channel is not enabled.
- * @retval TRUE         the channel is enabled.
+ * @param[in] pwmp      pointer to a @p PWMDriver object
  *
- * @notapi
+ * @api
  */
-bool_t pwm_lld_is_enabled(PWMDriver *pwmp, pwmchannel_t channel) {
+void pwm_lld_change_period(PWMDriver *pwmp, pwmcnt_t period) {
 
-  return FALSE;
 }
 
 /**
  * @brief   Enables a PWM channel.
+ * @pre     The PWM unit must have been activated using @p pwmStart().
+ * @post    The channel is active using the specified configuration.
+ * @note    Depending on the hardware implementation this function has
+ *          effect starting on the next cycle (recommended implementation)
+ *          or immediately (fallback implementation).
  *
  * @param[in] pwmp      pointer to a @p PWMDriver object
  * @param[in] channel   PWM channel identifier (0...PWM_CHANNELS-1)
@@ -119,11 +128,17 @@ void pwm_lld_enable_channel(PWMDriver *pwmp,
 
 /**
  * @brief   Disables a PWM channel.
- * @details The channel is disabled and its output line returned to the
+ * @pre     The PWM unit must have been activated using @p pwmStart().
+ * @post    The channel is disabled and its output line returned to the
  *          idle state.
+ * @note    Depending on the hardware implementation this function has
+ *          effect starting on the next cycle (recommended implementation)
+ *          or immediately (fallback implementation).
  *
  * @param[in] pwmp      pointer to a @p PWMDriver object
  * @param[in] channel   PWM channel identifier (0...PWM_CHANNELS-1)
+ *
+ * @notapi
  */
 void pwm_lld_disable_channel(PWMDriver *pwmp, pwmchannel_t channel) {
 
diff --git a/os/hal/templates/pwm_lld.h b/os/hal/templates/pwm_lld.h
index bee00c073..9ef7a9853 100644
--- a/os/hal/templates/pwm_lld.h
+++ b/os/hal/templates/pwm_lld.h
@@ -65,16 +65,13 @@ typedef uint8_t pwmchannel_t;
 typedef uint16_t pwmcnt_t;
 
 /**
- * @brief   Type of a structure representing an PWM driver.
+ * @brief PWM logic mode.
  */
-typedef struct PWMDriver PWMDriver;
-
-/**
- * @brief   PWM notification callback type.
- *
- * @param[in] pwmp      pointer to a @p PWMDriver object
- */
-typedef void (*pwmcallback_t)(PWMDriver *pwmp);
+typedef enum {
+  PWM_OUTPUT_DISABLED = 0,          /**< Output not driven, callback only.  */
+  PWM_OUTPUT_ACTIVE_HIGH = 1,       /**< Idle is logic level 0.             */
+  PWM_OUTPUT_ACTIVE_LOW = 2         /**< Idle is logic level 1.             */
+} pwmmode_t;
 
 /**
  * @brief   PWM driver channel configuration structure.
@@ -101,6 +98,18 @@ typedef struct {
  *          architecture dependent, fields.
  */
 typedef struct {
+  /**
+   * @brief   Timer clock in Hz.
+   * @note    The low level can use assertions in order to catch invalid
+   *          frequency specifications.
+   */
+  uint32_t                  frequency;
+  /**
+   * @brief   PWM period in ticks.
+   * @note    The low level can use assertions in order to catch invalid
+   *          period specifications.
+   */
+  pwmcnt_t                  period;
   /**
    * @brief Periodic callback pointer.
    * @note  This callback is invoked on PWM counter reset. If set to
@@ -128,6 +137,10 @@ struct PWMDriver {
    * @brief Current configuration data.
    */
   const PWMConfig           *config;
+  /**
+   * @brief   Current PWM period in ticks.
+   */
+  pwmcnt_t                  period;
 #if defined(PWM_DRIVER_EXT_FIELDS)
   PWM_DRIVER_EXT_FIELDS
 #endif
@@ -138,54 +151,6 @@ struct PWMDriver {
 /* Driver macros.                                                            */
 /*===========================================================================*/
 
-/**
- * @brief   Converts from fraction to pulse width.
- * @note    Be careful with rounding errors, this is integer math not magic.
- *          You can specify tenths of thousandth but make sure you have the
- *          proper hardware resolution by carefully choosing the clock source
- *          and prescaler settings, see @p PWM_COMPUTE_PSC.
- *
- * @param[in] pwmp      pointer to a @p PWMDriver object
- * @param[in] numerator numerator of the fraction
- * @param[in] denominator percentage as an integer between 0 and numerator
- * @return              The pulse width to be passed to @p pwmEnableChannel().
- *
- * @api
- */
-#define PWM_FRACTION_TO_WIDTH(pwmp, numerator, denominator) 0
-
-/**
- * @brief   Converts from degrees to pulse width.
- * @note    Be careful with rounding errors, this is integer math not magic.
- *          You can specify hundredths of degrees but make sure you have the
- *          proper hardware resolution by carefully choosing the clock source
- *          and prescaler settings, see @p PWM_COMPUTE_PSC.
- *
- * @param[in] pwmp      pointer to a @p PWMDriver object
- * @param[in] degrees   degrees as an integer between 0 and 36000
- * @return              The pulse width to be passed to @p pwmEnableChannel().
- *
- * @api
- */
-#define PWM_DEGREES_TO_WIDTH(pwmp, degrees)                                 \
-  PWM_FRACTION_TO_WIDTH(pwmp, 36000, degrees)
-
-/**
- * @brief   Converts from percentage to pulse width.
- * @note    Be careful with rounding errors, this is integer math not magic.
- *          You can specify tenths of thousandth but make sure you have the
- *          proper hardware resolution by carefully choosing the clock source
- *          and prescaler settings, see @p PWM_COMPUTE_PSC.
- *
- * @param[in] pwmp      pointer to a @p PWMDriver object
- * @param[in] percentage percentage as an integer between 0 and 10000
- * @return              The pulse width to be passed to @p pwmEnableChannel().
- *
- * @api
- */
-#define PWM_PERCENTAGE_TO_WIDTH(pwmp, percentage)                           \
-  PWM_FRACTION_TO_WIDTH(pwmp, 10000, percentage)
-
 /*===========================================================================*/
 /* External declarations.                                                    */
 /*===========================================================================*/
@@ -196,7 +161,7 @@ extern "C" {
   void pwm_lld_init(void);
   void pwm_lld_start(PWMDriver *pwmp);
   void pwm_lld_stop(PWMDriver *pwmp);
-  bool_t pwm_lld_is_enabled(PWMDriver *pwmp, pwmchannel_t channel);
+  void pwm_lld_change_period(PWMDriver *pwmp, pwmcnt_t period);
   void pwm_lld_enable_channel(PWMDriver *pwmp,
                               pwmchannel_t channel,
                               pwmcnt_t width);
diff --git a/readme.txt b/readme.txt
index ddc7c35f1..b0c085811 100644
--- a/readme.txt
+++ b/readme.txt
@@ -79,7 +79,14 @@
 - FIX: Fixed wrong checks in I/O Queues (bug 3219197)(backported to 2.2.3).
 - FIX: Fixed invalid assertion in adcConvert() (bug 3205410)(backported
   to 2.2.3).
-- NEW: Added new ICU driver model, Input Capture Unit..
+- NEW: Improvements to the PWM driver model:
+  - Easier configuration similar to the GPT driver initializations, macros
+    are no more required.
+  - Added a new function that allows to change the PWM period on the fly,
+    even from within callbacks. Formerly it was required to stop and restart
+    the driver.
+  - Improved driver documentation.
+- NEW: Added new ICU driver model, Input Capture Unit.
 - NEW: ICU driver implementation for STM32.
 - NEW: Implemented stack checking in the Cortex-Mx RVCT port (backported
   to 2.2.3).
diff --git a/testhal/STM32/PWM/main.c b/testhal/STM32/PWM/main.c
index c42b15939..ef08b792c 100644
--- a/testhal/STM32/PWM/main.c
+++ b/testhal/STM32/PWM/main.c
@@ -21,33 +21,21 @@
 #include "ch.h"
 #include "hal.h"
 
-/*
- * Red LEDs blinker thread, times are in milliseconds.
- */
-static WORKING_AREA(waThread1, 128);
-static msg_t Thread1(void *arg) {
-
-  (void)arg;
-  while (TRUE) {
-    palClearPad(IOPORT3, GPIOC_LED);
-    chThdSleepMilliseconds(500);
-    palSetPad(IOPORT3, GPIOC_LED);
-    chThdSleepMilliseconds(500);
-  }
-  return 0;
-}
-
 static void pwmpcb(PWMDriver *pwmp) {
 
   (void)pwmp;
+  palSetPad(IOPORT3, GPIOC_LED);
 }
 
 static void pwmc1cb(PWMDriver *pwmp) {
 
   (void)pwmp;
+  palClearPad(IOPORT3, GPIOC_LED);
 }
 
 static PWMConfig pwmcfg = {
+  10000,                                    /* 10KHz PWM clock frequency.   */
+  10000,                                    /* Initial PWM period 1S.       */
   pwmpcb,
   {
    {PWM_OUTPUT_ACTIVE_HIGH, pwmc1cb},
@@ -55,8 +43,6 @@ static PWMConfig pwmcfg = {
    {PWM_OUTPUT_DISABLED, NULL},
    {PWM_OUTPUT_DISABLED, NULL}
   },
-  PWM_COMPUTE_PSC(STM32_TIMCLK1, 10000),    /* 10KHz PWM clock frequency.   */
-  PWM_COMPUTE_ARR(10000, 1000000),          /* PWM period 1S.               */
   0
 };
 
@@ -76,9 +62,9 @@ int main(void) {
   chSysInit();
 
   /*
-   * Creates the blinker thread.
+   * LED initially off.
    */
-  chThdCreateStatic(waThread1, sizeof(waThread1), NORMALPRIO, Thread1, NULL);
+  palSetPad(IOPORT3, GPIOC_LED);
 
   /*
    * Initializes the PWM driver 1.
@@ -88,9 +74,9 @@ int main(void) {
   chThdSleepMilliseconds(2000);
 
   /*
-   * Starts the channel 0 using 50% duty cycle.
+   * Starts the channel 0 using 25% duty cycle.
    */
-  pwmEnableChannel(&PWMD1, 0, PWM_PERCENTAGE_TO_WIDTH(&PWMD1, 5000));
+  pwmEnableChannel(&PWMD1, 0, PWM_PERCENTAGE_TO_WIDTH(&PWMD1, 2500));
   chThdSleepMilliseconds(5000);
 
   /*
@@ -99,11 +85,19 @@ int main(void) {
   pwmEnableChannel(&PWMD1, 0, PWM_PERCENTAGE_TO_WIDTH(&PWMD1, 7500));
   chThdSleepMilliseconds(5000);
 
+  /*
+   * Changes PWM period to half second and duty cycle to 50%.
+   */
+  pwmChangePeriod(&PWMD1, 5000);
+  pwmEnableChannel(&PWMD1, 0, PWM_PERCENTAGE_TO_WIDTH(&PWMD1, 5000));
+  chThdSleepMilliseconds(5000);
+
   /*
    * Disables channel 0.
    */
   pwmDisableChannel(&PWMD1, 0);
-
+  pwmStop(&PWMD1);
+  palSetPad(IOPORT3, GPIOC_LED);
 
   /*
    * Normal main() thread activity, in this demo it does nothing.