Diff: Device/FastPWM_STM_TIM.cpp

Revision:

0:16be67f4d9ac

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Device/FastPWM_STM_TIM.cpp	Tue Sep 19 16:52:01 2017 +0000
@@ -0,0 +1,75 @@
+//This should (hopefully) work on all STM targets which use TIM timers for PWM
+
+#ifdef TARGET_STM
+
+#include "FastPWM.h"
+
+typedef __IO uint32_t* CHANNEL_P_T;
+
+typedef struct  {
+    CHANNEL_P_T channel;
+    uint32_t clk_prescaler;
+} fastpwm_struct;
+
+#define PWM_CHANNEL         ((((fastpwm_struct*)fast_obj)->channel)) 
+#define PWM_CLK_PRESCALER   ((((fastpwm_struct*)fast_obj)->clk_prescaler))
+#define PWM_TIMER           ((TIM_TypeDef*)_pwm.pwm)
+
+#if defined(TARGET_STM32F0) || defined (TARGET_STM32F1) || defined (TARGET_STM32L1)
+extern __IO uint32_t* getChannel(TIM_TypeDef* pwm, PinName pin);
+#endif
+
+void FastPWM::initFastPWM( void ) {
+    fast_obj = new fastpwm_struct;
+    #if defined(TARGET_STM32F0) || defined (TARGET_STM32F1) || defined (TARGET_STM32L1)
+    PWM_CHANNEL = getChannel(PWM_TIMER, _pwm.pin);
+    #else
+    PWM_CHANNEL = (&PWM_TIMER->CCR1 + _pwm.channel - 1); 
+    #endif
+    
+    // Depending on the timer and the internal bus it is connected to, each STM timer
+    // can have a fixed prescaler from the clock, especially the faster devices.
+    // In order not to have to hardcode this in, we use knowledge that mbed lib sets
+    // default period to 20ms to reverse engineer the prescaler from this. 
+    uint32_t current_hz = SystemCoreClock / (PWM_TIMER->PSC + 1) / (PWM_TIMER->ARR+1);
+    PWM_CLK_PRESCALER = (current_hz + 1) / 50;  //50Hz is magic number it should be, +1 is to handle possible rounding errors in mbed setup
+    
+    //Sanity check in case a target does something different
+    if ( (PWM_CLK_PRESCALER == 0 ) || (PWM_CLK_PRESCALER > 16)) {
+        PWM_CLK_PRESCALER = 1;
+    }
+    
+    //Enable PWM period syncing for glitch free result
+    PWM_TIMER->CR1 |= TIM_CR1_ARPE;
+    
+    bits = 16;
+}
+
+void FastPWM::pulsewidth_ticks( uint32_t ticks ) {
+    *PWM_CHANNEL = ticks;    
+}
+
+void FastPWM::period_ticks( uint32_t ticks ) {
+    PWM_TIMER->ARR = ticks - 1;
+}
+
+uint32_t FastPWM::getPeriod( void ) {
+    return PWM_TIMER->ARR + 1;
+}
+
+uint32_t FastPWM::setPrescaler(uint32_t reqScale) {
+    if (reqScale == 0) {
+        //Return prescaler
+        return (PWM_TIMER->PSC + 1) * PWM_CLK_PRESCALER;
+    }
+    if (reqScale > (uint32_t)(PWM_CLK_PRESCALER<<16)) {
+        reqScale = PWM_CLK_PRESCALER<<16;
+    }
+    //Else set prescaler, we have to substract one from reqScale since a 0 in PCVAL is prescaler of 1
+    //Take into account PWM_CLK_PRESCALER, we need to make sure reqScale is always rounded up
+    PWM_TIMER->PSC = (reqScale + PWM_CLK_PRESCALER - 1)/PWM_CLK_PRESCALER - 1;
+
+    return setPrescaler(0);
+}
+
+#endif
\ No newline at end of file