Add 'wait_for_pulse' to ap3_pwm_output

This waits until a pulse has just been completed to change the compare register values. This attempts to solve isse #16.

servoWrite could cause the signal to be inverted if/when the compare registers were changed at the same time that they matched the timer. This attempts to wait until the timer value is below the smaller compare register to make any changes.

Author: oclyke

cores/arduino/ard_sup/analog/ap3_analog.cpp

@@ -354,6 +354,37 @@ ap3_err_t ap3_change_channel(uint8_t padNumber)
 }
 
 
+void ap3_pwm_wait_for_pulse(uint32_t timer, uint32_t segment, uint32_t output, uint32_t margin){
+
+    volatile uint32_t *pui32CompareReg;
+    volatile uint32_t ctimer_val;
+    uint32_t cmpr0;
+
+    // Get the comapre register address
+    if( segment == AM_HAL_CTIMER_TIMERA ){
+        if( output == AM_HAL_CTIMER_OUTPUT_NORMAL ){
+            pui32CompareReg = (uint32_t*)CTIMERADDRn(CTIMER, timer, CMPRA0);
+        }else{
+            pui32CompareReg = (uint32_t*)CTIMERADDRn(CTIMER, timer, CMPRAUXA0);
+        }
+    }else{
+        if( output == AM_HAL_CTIMER_OUTPUT_NORMAL ){
+            pui32CompareReg = (uint32_t*)CTIMERADDRn(CTIMER, timer, CMPRB0);
+        }else{
+            pui32CompareReg = (uint32_t*)CTIMERADDRn(CTIMER, timer, CMPRAUXB0);
+        }
+    }
+
+    // Get the compare value
+    cmpr0 = ((uint32_t)(*(pui32CompareReg)) & 0x0000FFFF);
+    
+    // Wait for the timer value to be less than the compare value so that it is safe to change
+    ctimer_val = am_hal_ctimer_read( timer, segment);
+    while( (ctimer_val + 0) > cmpr0 ){
+        ctimer_val = am_hal_ctimer_read( timer, segment);
+    }
+}
+
 //**********************************************
 // ap3_pwm_output
 // - This function allows you to specify an arbitrary pwm output signal with a given frame width (fw) and time high (th). 
@@ -476,6 +507,9 @@ ap3_err_t ap3_pwm_output(uint8_t pin, uint32_t th, uint32_t fw, uint32_t clk)
                                 // (AM_HAL_CTIMER_FN_PWM_REPEAT | AP3_ANALOG_CLK | AM_HAL_CTIMER_INT_ENABLE) );
                                 (AM_HAL_CTIMER_FN_PWM_REPEAT | clk));
 
+    // Wait until after high pulse to change the state (avoids inversion)
+    ap3_pwm_wait_for_pulse( timer, segment, output, 10);
+
     // If this pad uses secondary output:
     if (output == AM_HAL_CTIMER_OUTPUT_SECONDARY)
     {