Fix PWM flickering at low levels (arendst#7415)

tasmota/CHANGELOG.md

@@ -4,6 +4,7 @@
 
 - Change wifi connectivity stability (#7602)
 - Add ``SetOption84 1`` sends AWS IoT device shadow updates (alternative to retained)
+- Fix PWM flickering at low levels (#7415)
 
 ### 8.1.0.4 20200116
 

tasmota/core_esp8266_waveform.cpp

@@ -0,0 +1,317 @@
+/*
+  esp8266_waveform - General purpose waveform generation and control,
+                     supporting outputs on all pins in parallel.
+
+  Copyright (c) 2018 Earle F. Philhower, III.  All rights reserved.
+
+  The core idea is to have a programmable waveform generator with a unique
+  high and low period (defined in microseconds).  TIMER1 is set to 1-shot
+  mode and is always loaded with the time until the next edge of any live
+  waveforms.
+
+  Up to one waveform generator per pin supported.
+
+  Each waveform generator is synchronized to the ESP cycle counter, not the
+  timer.  This allows for removing interrupt jitter and delay as the counter
+  always increments once per 80MHz clock.  Changes to a waveform are
+  contiguous and only take effect on the next waveform transition,
+  allowing for smooth transitions.
+
+  This replaces older tone(), analogWrite(), and the Servo classes.
+
+  Everywhere in the code where "cycles" is used, it means ESP.getCycleTime()
+  cycles, not TIMER1 cycles (which may be 2 CPU clocks @ 160MHz).
+
+  This library is free software; you can redistribute it and/or
+  modify it under the terms of the GNU Lesser General Public
+  License as published by the Free Software Foundation; either
+  version 2.1 of the License, or (at your option) any later version.
+
+  This library is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public
+  License along with this library; if not, write to the Free Software
+  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
+*/
+
+// Use PWM from core 2.4.0 as all versions below 2.5.0-beta3 produce LED flickering when settings are saved to flash
+#include <core_version.h>
+#if defined(ARDUINO_ESP8266_RELEASE_2_6_1) || defined(ARDUINO_ESP8266_RELEASE_2_6_2) || defined(ARDUINO_ESP8266_RELEASE_2_6_3)
+#warning **** Tasmota is using a patched PWM Arduino version as planned ****
+
+
+#include <Arduino.h>
+#include "ets_sys.h"
+#include "core_esp8266_waveform.h"
+
+extern "C" {
+
+// Maximum delay between IRQs
+#define MAXIRQUS (10000)
+
+// Set/clear GPIO 0-15 by bitmask
+#define SetGPIO(a) do { GPOS = a; } while (0)
+#define ClearGPIO(a) do { GPOC = a; } while (0)
+
+// Waveform generator can create tones, PWM, and servos
+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 nextTimeHighCycles; // Copy over low->high to keep smooth waveform
+  uint32_t nextTimeLowCycles;  // Copy over high->low to keep smooth waveform
+} Waveform;
+
+static Waveform waveform[17];        // State of all possible pins
+static volatile uint32_t waveformState = 0;   // Is the pin high or low, updated in NMI so no access outside the NMI code
+static volatile uint32_t waveformEnabled = 0; // Is it actively running, updated in NMI so no access outside the NMI code
+
+// Enable lock-free by only allowing updates to waveformState and waveformEnabled from IRQ service routine
+static volatile uint32_t waveformToEnable = 0;  // Message to the NMI handler to start a waveform on a inactive pin
+static volatile uint32_t waveformToDisable = 0; // Message to the NMI handler to disable a pin from waveform generation
+
+static uint32_t (*timer1CB)() = NULL;
+
+
+// Non-speed critical bits
+#pragma GCC optimize ("Os")
+
+static inline ICACHE_RAM_ATTR uint32_t GetCycleCount() {
+  uint32_t ccount;
+  __asm__ __volatile__("esync; rsr %0,ccount":"=a"(ccount));
+  return ccount;
+}
+
+// Interrupt on/off control
+static ICACHE_RAM_ATTR void timer1Interrupt();
+static bool timerRunning = false;
+
+static void initTimer() {
+  timer1_disable();
+  ETS_FRC_TIMER1_INTR_ATTACH(NULL, NULL);
+  ETS_FRC_TIMER1_NMI_INTR_ATTACH(timer1Interrupt);
+  timer1_enable(TIM_DIV1, TIM_EDGE, TIM_SINGLE);
+  timerRunning = true;
+}
+
+static void ICACHE_RAM_ATTR deinitTimer() {
+  ETS_FRC_TIMER1_NMI_INTR_ATTACH(NULL);
+  timer1_disable();
+  timer1_isr_init();
+  timerRunning = false;
+}
+
+// Set a callback.  Pass in NULL to stop it
+void setTimer1Callback(uint32_t (*fn)()) {
+  timer1CB = fn;
+  if (!timerRunning && fn) {
+    initTimer();
+    timer1_write(microsecondsToClockCycles(1)); // Cause an interrupt post-haste
+  } else if (timerRunning && !fn && !waveformEnabled) {
+    deinitTimer();
+  }
+}
+
+// Start up a waveform on a pin, or change the current one.  Will change to the new
+// 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 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->expiryCycle = 1; // expiryCycle==0 means no timeout, so avoid setting it
+  }
+
+  uint32_t mask = 1<<pin;
+  if (!(waveformEnabled & mask)) {
+    // Actually set the pin high or low in the IRQ service to guarantee times
+    wave->nextServiceCycle = GetCycleCount() + microsecondsToClockCycles(1);
+    waveformToEnable |= mask;
+    if (!timerRunning) {
+      initTimer();
+      timer1_write(microsecondsToClockCycles(10));
+    } else {
+      // Ensure timely service....
+      if (T1L > microsecondsToClockCycles(10)) {
+        timer1_write(microsecondsToClockCycles(10));
+      }
+    }
+    while (waveformToEnable) {
+      delay(0); // Wait for waveform to update
+    }
+  }
+
+  return true;
+}
+
+// Speed critical bits
+#pragma GCC optimize ("O2")
+// Normally would not want two copies like this, but due to different
+// optimization levels the inline attribute gets lost if we try the
+// other version.
+
+static inline ICACHE_RAM_ATTR uint32_t GetCycleCountIRQ() {
+  uint32_t ccount;
+  __asm__ __volatile__("rsr %0,ccount":"=a"(ccount));
+  return ccount;
+}
+
+static inline ICACHE_RAM_ATTR uint32_t min_u32(uint32_t a, uint32_t b) {
+  if (a < b) {
+    return a;
+  }
+  return b;
+}
+
+// Stops a waveform on a pin
+int ICACHE_RAM_ATTR stopWaveform(uint8_t pin) {
+  // Can't possibly need to stop anything if there is no timer active
+  if (!timerRunning) {
+    return false;
+  }
+  // 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
+  uint32_t mask = 1<<pin;
+  if (!(waveformEnabled & mask)) {
+    return false; // It's not running, nothing to do here
+  }
+  waveformToDisable |= mask;
+  // Ensure timely service....
+  if (T1L > microsecondsToClockCycles(10)) {
+    timer1_write(microsecondsToClockCycles(10));
+  }
+  while (waveformToDisable) {
+    /* no-op */ // Can't delay() since stopWaveform may be called from an IRQ
+  }
+  if (!waveformEnabled && !timer1CB) {
+    deinitTimer();
+  }
+  return true;
+}
+
+// The SDK and hardware take some time to actually get to our NMI code, so
+// decrement the next IRQ's timer value by a bit so we can actually catch the
+// real CPU cycle counter we want for the waveforms.
+#if F_CPU == 80000000
+  #define DELTAIRQ (microsecondsToClockCycles(3))
+#else
+  #define DELTAIRQ (microsecondsToClockCycles(2))
+#endif
+
+
+static ICACHE_RAM_ATTR void timer1Interrupt() {
+  // 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.
+  static int startPin = 0;
+  static int endPin = 0;
+
+  uint32_t nextEventCycles = microsecondsToClockCycles(MAXIRQUS);
+  uint32_t timeoutCycle = GetCycleCountIRQ() + microsecondsToClockCycles(14);
+
+  if (waveformToEnable || waveformToDisable) {
+    // Handle enable/disable requests from main app.
+    waveformEnabled = (waveformEnabled & ~waveformToDisable) | waveformToEnable; // Set the requested waveforms on/off
+    waveformState &= ~waveformToEnable;  // And clear the state of any just started
+    waveformToEnable = 0;
+    waveformToDisable = 0;
+    // Find the first GPIO being generated by checking GCC's find-first-set (returns 1 + the bit of the first 1 in an int32_t)
+    startPin = __builtin_ffs(waveformEnabled) - 1;
+    // Find the last bit by subtracting off GCC's count-leading-zeros (no offset in this one)
+    endPin = 32 - __builtin_clz(waveformEnabled);
+  }
+
+  bool done = false;
+  if (waveformEnabled) {
+    do {
+      nextEventCycles = microsecondsToClockCycles(MAXIRQUS);
+      for (int i = startPin; i <= endPin; i++) {
+        uint32_t mask = 1<<i;
+
+        // If it's not on, ignore!
+        if (!(waveformEnabled & mask)) {
+          continue;
+        }
+
+        Waveform *wave = &waveform[i];
+        uint32_t now = GetCycleCountIRQ();
+
+        // Disable any waveforms that are done
+        if (wave->expiryCycle) {
+          int32_t expiryToGo = wave->expiryCycle - now;
+          if (expiryToGo < 0) {
+              // Done, remove!
+              waveformEnabled &= ~mask;
+              if (i == 16) {
+                GP16O &= ~1;
+              } else {
+                ClearGPIO(mask);
+              }
+              continue;
+            }
+        }
+
+        // Check for toggles
+        int32_t cyclesToGo = wave->nextServiceCycle - now;
+        if (cyclesToGo < 0) {
+          waveformState ^= mask;
+          if (waveformState & mask) {
+            if (i == 16) {
+              GP16O |= 1; // GPIO16 write slow as it's RMW
+            } else {
+              SetGPIO(mask);
+            }
+            wave->nextServiceCycle = now + wave->nextTimeHighCycles + cyclesToGo;
+            nextEventCycles = min_u32(nextEventCycles, min_u32(wave->nextTimeHighCycles + cyclesToGo, 1));
+          } else {
+            if (i == 16) {
+              GP16O &= ~1; // GPIO16 write slow as it's RMW
+            } else {
+              ClearGPIO(mask);
+            }
+            wave->nextServiceCycle = now + wave->nextTimeLowCycles + cyclesToGo;
+            nextEventCycles = min_u32(nextEventCycles, min_u32(wave->nextTimeLowCycles + cyclesToGo, 1));
+          }
+        } else {
+          uint32_t deltaCycles = wave->nextServiceCycle - now;
+          nextEventCycles = min_u32(nextEventCycles, deltaCycles);
+        }
+      }
+
+      // Exit the loop if we've hit the fixed runtime limit or the next event is known to be after that timeout would occur
+      uint32_t now = GetCycleCountIRQ();
+      int32_t cycleDeltaNextEvent = timeoutCycle - (now + nextEventCycles);
+      int32_t cyclesLeftTimeout = timeoutCycle - now;
+      done = (cycleDeltaNextEvent < 0) || (cyclesLeftTimeout < 0);
+    } while (!done);
+  } // if (waveformEnabled)
+
+  if (timer1CB) {
+    nextEventCycles = min_u32(nextEventCycles, timer1CB());
+  }
+
+  if (nextEventCycles < microsecondsToClockCycles(10)) {
+    nextEventCycles = microsecondsToClockCycles(10);
+  }
+  nextEventCycles -= DELTAIRQ;
+
+  // Do it here instead of global function to save time and because we know it's edge-IRQ
+#if F_CPU == 160000000
+  T1L = nextEventCycles >> 1; // Already know we're in range by MAXIRQUS
+#else
+  T1L = nextEventCycles; // Already know we're in range by MAXIRQUS
+#endif
+  TEIE |= TEIE1; // Edge int enable
+}
+
+};
+
+#endif  // ARDUINO_ESP8266_RELEASE