Save IRAM/heap by adjusting WVF update struct

The waveform update structure included 2 32-bit quantities (so, used 8 * 17 = 136 bytes of RAM) for the next cycle of a waveform. Replace that with a single update register, in a posted fashion. The logic now sets the new state of a single waveform and returns immediately (so, no need to wait 1ms if you've got an existing waveform of 1khz). The waveform NMI will pick up the changed value on its next cycle. Reduces IRAM by 40 bytes, and heap by 144 bytes.
esp8266 · earlephilhower · Nov 20, 2020 · Apr 19, 2020 · Apr 19, 2020 · Apr 19, 2020
commit c8b53ef7c285b882a6916f372daf6fe2cc76fc15
diff --git a/cores/esp8266/core_esp8266_waveform.cpp b/cores/esp8266/core_esp8266_waveform.cpp
@@ -55,13 +55,11 @@ extern "C" {
 typedef struct {
   uint32_t nextServiceCycle;   // ESP cycle timer when a transition required
   uint32_t expiryCycle;        // For time-limited waveform, the cycle when this waveform must stop
-  uint32_t timeHighCycles;     // Currently running waveform period
+  uint32_t timeHighCycles;     // Actual running waveform period (adjusted using desiredCycles)
   uint32_t timeLowCycles;      //
-  uint32_t desiredHighCycles;     // Currently running waveform period
-  uint32_t desiredLowCycles;      //
-  uint32_t gotoTimeHighCycles; // Copied over on the next period to preserve phase
-  uint32_t gotoTimeLowCycles;  //
-  uint32_t lastEdge; //
+  uint32_t desiredHighCycles;  // Ideal waveform period to drive the error signal
+  uint32_t desiredLowCycles;   //
+  
8000
uint32_t lastEdge;           // Cycle when this generator last changed
 } Waveform;
 
 class WVFState {
@@ -74,7 +72,7 @@ class WVFState {
   uint32_t waveformToEnable = 0;  // Message to the NMI handler to start a waveform on a inactive pin
   uint32_t waveformToDisable = 0; // Message to the NMI handler to disable a pin from waveform generation
 
-  int32_t waveformToChange = -1;
+  uint32_t waveformToChange = 0; // Mask of pin to change. One bit set in main app, cleared when effected in the NMI
   uint32_t waveformNewHigh = 0;
   uint32_t waveformNewLow = 0;
 
@@ -83,8 +81,8 @@ class WVFState {
   // Optimize the NMI inner loop by keeping track of the min and max GPIO that we
   // are generating.  In the common case (1 PWM) these may be the same pin and
   // we can avoid looking at the other pins.
-  int startPin = 0;
-  int endPin = 0;
+  uint16_t startPin = 0;
+  uint16_t endPin = 0;
 };
 static WVFState wvfState;
 
@@ -318,22 +316,22 @@ int startWaveformClockCycles(uint8_t pin, uint32_t timeHighCycles, uint32_t time
   uint32_t mask = 1<<pin;
   MEMBARRIER();
   if (wvfState.waveformEnabled & mask) {
-    wvfState.waveformNewHigh = timeHighCycles;
-    wvfState.waveformNewLow = timeLowCycles;
-    MEMBARRIER();
-    wvfState.waveformToChange = pin;
-    while (wvfState.waveformToChange >= 0) {
+    // Make sure no waveform changes are waiting to be applied
+    while (wvfState.waveformToChange) {
       delay(0); // Wait for waveform to update
       // No mem barrier here, the call to a global function implies global state updated
     }
+    wvfState.waveformNewHigh = timeHighCycles;
+    wvfState.waveformNewLow = timeLowCycles;
+    MEMBARRIER();
+    wvfState.waveformToChange = mask;
+    // The waveform will be updated some time in the future on the next period for the signal
   } else { //  if (!(wvfState.waveformEnabled & mask)) {
     wave->timeHighCycles = timeHighCycles;
     wave->timeLowCycles = timeLowCycles;
     wave->desiredHighCycles = wave->timeHighCycles;
     wave->desiredLowCycles = wave->timeLowCycles;
     wave->lastEdge = 0;
-    wave->gotoTimeHighCycles = wave->timeHighCycles;
-    wave->gotoTimeLowCycles = wave->timeLowCycles;    // Actually set the pin high or low in the IRQ service to guarantee times
     wave->nextServiceCycle = ESP.getCycleCount() + microsecondsToClockCycles(1);
     wvfState.waveformToEnable |= mask;
     MEMBARRIER();
@@ -387,8 +385,13 @@ int ICACHE_RAM_ATTR stopWaveform(uint8_t pin) {
   }
   // If user sends in a pin >16 but <32, this will always point to a 0 bit
   // If they send >=32, then the shift will result in 0 and it will also return false
-  if (wvfState.waveformEnabled & (1UL << pin)) {
-    wvfState.waveformToDisable = 1UL << pin;
+  uint32_t mask = 1<<pin;
+  if (wvfState.waveformEnabled & mask) {
+    wvfState.waveformToDisable = mask;
+    // Cancel any pending updates for this waveform, too.
+    if (wvfState.waveformToChange & mask) {
+        wvfState.waveformToChange = 0;
+    }
     forceTimerInterrupt();
     while (wvfState.waveformToDisable) {
       MEMBARRIER(); // If it wasn't written yet, it has to be by now
@@ -450,11 +453,6 @@ static ICACHE_RAM_ATTR void timer1Interrupt() {
     pwmState.nextServiceCycle = GetCycleCountIRQ(); // Do it this loop!
     // No need for mem barrier here.  Global must be written by IRQ exit
 #endif
-  } else if (wvfState.waveformToChange >= 0) {
-    wvfState.waveform[wvfState.waveformToChange].gotoTimeHighCycles = wvfState.waveformNewHigh;
-    wvfState.waveform[wvfState.waveformToChange].gotoTimeLowCycles = wvfState.waveformNewLow;
-    wvfState.waveformToChange = -1;
-    // No need for memory barrier here.  The global has to be written before exit the ISR.
   }
 
   bool done = false;
@@ -541,13 +539,13 @@ static ICACHE_RAM_ATTR void timer1Interrupt() {
             } else {
               SetGPIO(mask);
             }
-            if (wave->gotoTimeHighCycles) {
+            if (wvfState.waveformToChange & mask) {
               // Copy over next full-cycle timings
-              wave->timeHighCycles = wave->gotoTimeHighCycles;
-              wave->desiredHighCycles = wave->gotoTimeHighCycles;
-              wave->timeLowCycles = wave->gotoTimeLowCycles;
-              wave->desiredLowCycles = wave->gotoTimeLowCycles;
-              wave->gotoTimeHighCycles = 0;
+              wave->timeHighCycles = wvfState.waveformNewHigh;
+              wave->desiredHighCycles = wvfState.waveformNewHigh;
+              wave->timeLowCycles = wvfState.waveformNewLow;
+              wave->desiredLowCycles = wvfState.waveformNewLow;
+              wvfState.waveformToChange = 0;
             } else {
 #ifdef ENABLE_FEEDBACK
               if (wave->lastEdge) {