(0.15.x) wait for LEDs output to finish before OS calls that potentially suspend interrupts

wled00/FX.h

@@ -816,8 +816,9 @@ class WS2812FX {  // 96 bytes
     inline void setShowCallback(show_callback cb)             { _callback = cb; }
     inline void setTransition(uint16_t t)                     { _transitionDur = t; } // sets transition time (in ms)
     inline void appendSegment(const Segment &seg = Segment()) { if (_segments.size() < getMaxSegments()) _segments.push_back(seg); }
-    inline void suspend()                                     { _suspend = true; }    // will suspend (and canacel) strip.service() execution
+    inline void suspend()                                     { _suspend = true; }    // will suspend (and cancel) strip.service() execution
     inline void resume()                                      { _suspend = false; }   // will resume strip.service() execution
+    inline bool isSuspended()                                 { return _suspend; }    // true if strip.service() execution is suspended
 
     bool
       paletteFade,
@@ -827,6 +828,11 @@ class WS2812FX {  // 96 bytes
       isUpdating() const, // return true if the strip is being sent pixel updates
       deserializeMap(uint8_t n=0);
 
+    // be nice, but not too nice - wait until LEDs are idle, or maxWaitMS have passed
+    // on 8266 this call will _not_ wait outside of the main loop context
+    // returns isUpdating() status after waiting
+    bool waitForLEDs(unsigned maxWaitMS) const;
+
     inline bool isServicing() const          { return _isServicing; }           // returns true if strip.service() is executing
     inline bool hasWhiteChannel() const      { return _hasWhiteChannel; }       // returns true if strip contains separate white chanel
     inline bool isOffRefreshRequired() const { return _isOffRefreshRequired; }  // returns true if strip requires regular updates (i.e. TM1814 chipset)

wled00/FX_fcn.cpp

@@ -1476,6 +1476,27 @@ bool WS2812FX::isUpdating() const {
   return !BusManager::canAllShow();
 }
 
+/**
+ * Be nice, but not too nice - wait util LEDs are idle, or maxWaitMS milliseconds have passed
+ * On 8266 this call will _not_ wait outside the main loop context
+ *   Function returns isUpdating() status after waiting
+ */
+bool WS2812FX::waitForLEDs(unsigned maxWaitMS) const {
+  #ifdef ARDUINO_ARCH_ESP32
+    unsigned long waitStart = millis();
+    while (strip.isUpdating() && (millis() - waitStart < maxWaitMS)) delay(1);
+  #else
+    if (can_yield()) {
+      // If we are in a yieldable context (main loop), wait until the LEDs output finishes
+      yield();
+      unsigned long waitStart = millis();
+      while (strip.isUpdating() && (millis() - waitStart < maxWaitMS)) delay(1);
+      yield();
+    }
+  #endif
+  return isUpdating();
+}
+
 /**
  * Returns the refresh rate of the LED strip. Useful for finding out whether a given setup is fast enough.
  * Only updates on show() or is set to 0 fps if last show is more than 2 secs ago, so accuracy varies

wled00/file.cpp

@@ -34,13 +34,26 @@ static File f; // don't export to other cpp files
 
 //wrapper to find out how long closing takes
 void closeFile() {
+  if (!doCloseFile || !f) { doCloseFile = false; return; }  // file not open, or no request to close -> nothing to do, nothing to wait
   #ifdef WLED_DEBUG_FS
     DEBUGFS_PRINT(F("Close -> "));
     uint32_t s = millis();
   #endif
+  doCloseFile = false; // consume flag early, to reduce the time window for concurrent closing attempts from several tasks.
+
+  // f.close() flushes to flash and briefly disables cache-related interrupts on ESP8266,
+  // which can corrupt WS281x LED timing (bit-bang / UART) if it coincides with strip.service().
+  bool haveSuspended = false;
+  #if defined(WLED_USE_SHARED_RMT) || defined(__riscv) || !defined(ARDUINO_ARCH_ESP32)
+  if (!strip.isSuspended()) { strip.suspend(); haveSuspended = true; }// prevent that a new strip.show() starts after waiting
+  strip.waitForLEDs(15); // be nice, but not too nice. Waits up to 15ms
+  #endif
+
+  // In 8266 async webserver / lwIP interrupt context can_yield() is false and we cannot wait,
+  // so we proceed immediately — the close is still required to prevent file corruption.
   f.close(); // "if (f)" check is aleady done inside f.close(), and f cannot be nullptr -> no need for double checking before closing the file handle.
+  if (haveSuspended) strip.resume();  // end of critical section - new LEDs updates are allowed again
   DEBUGFS_PRINTF("took %d ms\n", millis() - s);
-  doCloseFile = false;
 }
 
 //find() that reads and buffers data from file stream in 256-byte blocks.

wled00/json.cpp

@@ -771,6 +771,13 @@ void serializeInfo(JsonObject root)
   root[F("lwip")] = LWIP_VERSION_MAJOR;
 #endif
 
+  bool haveSuspended = false;
+#if defined(WLED_USE_SHARED_RMT) || defined(__riscv) || !defined(ARDUINO_ARCH_ESP32)
+  // calling ESP.getFreeHeap() during led update causes glitches on C3 and possibly on 8266, too
+  if (!strip.isSuspended()) { strip.suspend(); haveSuspended = true; } // prevent that a new strip.show() starts after waiting
+  strip.waitForLEDs(15); // be nice, but not too nice. Waits up to 15ms
+#endif
+
   root[F("freeheap")] = ESP.getFreeHeap();
   #if defined(ARDUINO_ARCH_ESP32)
   if (psramSafe && psramFound()) root[F("psram")] = ESP.getFreePsram();
@@ -781,6 +788,7 @@ void serializeInfo(JsonObject root)
   getTimeString(time);
   root[F("time")] = time;
 
+  if (haveSuspended) strip.resume();  // end of critical section - new LEDs updates are allowed again
   UsermodManager::addToJsonInfo(root);
 
   uint16_t os = 0;

wled00/wled.cpp

@@ -163,6 +163,11 @@ void WLED::loop()
 
   // reconnect WiFi to clear stale allocations if heap gets too low
   if (millis() - heapTime > 15000) {
+    #if defined(WLED_USE_SHARED_RMT) || defined(__riscv) || !defined(ARDUINO_ARCH_ESP32)
+    // calling ESP.getFreeHeap() during led update causes glitches on C3 and possibly on 8266, too
+    strip.waitForLEDs(15); // wait up to 15ms for LEDs sendout to complete - we are in the main loop, so a new strip.show() cannot start while waiting
+    #endif
+
     uint32_t heap = ESP.getFreeHeap();
     if (heap < MIN_HEAP_SIZE && lastHeap < MIN_HEAP_SIZE) {
       DEBUG_PRINTF_P(PSTR("Heap too low! %u\n"), heap);      

wled00/wled_server.cpp

@@ -175,7 +175,14 @@ static void handleUpload(AsyncWebServerRequest *request, const String& filename,
     request->_tempFile.write(data,len);
   }
   if (final) {
+    bool haveSuspended = false;
+    #if defined(WLED_USE_SHARED_RMT) || defined(__riscv) || !defined(ARDUINO_ARCH_ESP32)
+      if (!strip.isSuspended()) { strip.suspend(); haveSuspended = true; } // prevent that a new strip.show() starts after waiting
+      strip.waitForLEDs(25); // calling file.close() during LEDs sendout can cause glitches on C3 and on 8266
+    #endif
     request->_tempFile.close();
+    if (haveSuspended) strip.resume();
+
     if (filename.indexOf(F("cfg.json")) >= 0) { // check for filename with or without slash
       doReboot = true;
       request->send(200, FPSTR(CONTENT_TYPE_PLAIN), F("Configuration restore successful.\nRebooting..."));