Allow waveforms to be specified in clock cycles

Allow the PWM to specify sub-microsecond waveform edges, as have been
proposed by @dok-net and me.  No other changes intended.

This will increase the linearity at 30 and 40 kHZ PWM rates, but leave
most other things unaffected.

Author: earlephilhower

cores/esp8266/core_esp8266_waveform.cpp

@@ -112,15 +112,19 @@ void setTimer1Callback(uint32_t (*fn)()) {
 // waveform smoothly on next low->high transition.  For immediate change, stopWaveform()
 // first, then it will immediately begin.
 int startWaveform(uint8_t pin, uint32_t timeHighUS, uint32_t timeLowUS, uint32_t runTimeUS) {
-  if ((pin > 16) || isFlashInterfacePin(pin)) {
+  return startWaveformCycles(pin, microsecondsToClockCycles(timeHighUS), microsecondsToClockCycles(timeLowUS), microsecondsToClockCycles(runTimeUS));
+}
+
+int startWaveformCycles(uint8_t pin, uint32_t timeHighCycles, uint32_t timeLowCycles, uint32_t runTimeCycles) {
+   if ((pin > 16) || isFlashInterfacePin(pin)) {
     return false;
   }
   Waveform *wave = &waveform[pin];
   // Adjust to shave off some of the IRQ time, approximately
-  wave->nextTimeHighCycles = microsecondsToClockCycles(timeHighUS);
-  wave->nextTimeLowCycles = microsecondsToClockCycles(timeLowUS);
-  wave->expiryCycle = runTimeUS ? GetCycleCount() + microsecondsToClockCycles(runTimeUS) : 0;
-  if (runTimeUS && !wave->expiryCycle) {
+  wave->nextTimeHighCycles = timeHighCycles;
+  wave->nextTimeLowCycles = timeLowCycles;
+  wave->expiryCycle = runTimeCycles ? GetCycleCount() + runTimeCycles : 0;
+  if (runTimeCycles && !wave->expiryCycle) {
     wave->expiryCycle = 1; // expiryCycle==0 means no timeout, so avoid setting it
   }
 

cores/esp8266/core_esp8266_waveform.h

@@ -50,6 +50,8 @@ extern "C" {
 // If runtimeUS > 0 then automatically stop it after that many usecs.
 // Returns true or false on success or failure.
 int startWaveform(uint8_t pin, uint32_t timeHighUS, uint32_t timeLowUS, uint32_t runTimeUS);
+// Same as above, but pass in CPU clock cycles instead of microseconds
+int startWaveformCycles(uint8_t pin, uint32_t timeHighCycles, uint32_t timeLowCycles, uint32_t runTimeCycles);
 // Stop a waveform, if any, on the specified pin.
 // Returns true or false on success or failure.
 int stopWaveform(uint8_t pin);

cores/esp8266/core_esp8266_wiring_pwm.cpp

@@ -25,6 +25,7 @@
 #include "core_esp8266_waveform.h"
 
 extern "C" {
+#include "user_interface.h"
 
 static uint32_t analogMap = 0;
 static int32_t analogScale = PWMRANGE;
@@ -50,7 +51,7 @@ extern void __analogWrite(uint8_t pin, int val) {
   if (pin > 16) {
     return;
   }
-  uint32_t analogPeriod = 1000000L / analogFreq;
+  uint32_t analogPeriod = (1000000L * system_get_cpu_freq()) / analogFreq;
   if (val < 0) {
     val = 0;
   } else if (val > analogScale) {
@@ -68,7 +69,7 @@ extern void __analogWrite(uint8_t pin, int val) {
     stopWaveform(pin);
     digitalWrite(pin, LOW);
   } else {
-    if (startWaveform(pin, high, low, 0)) {
+    if (startWaveformCycles(pin, high, low, 0)) {
       analogMap |= (1 << pin);
     }
   }