ESP32 HAL: Fix random pauses during prints

Marlin/src/HAL/HAL_ESP32/HAL.h

@@ -137,3 +137,44 @@ void HAL_adc_start_conversion(uint8_t adc_pin);
 void HAL_idletask();
 void HAL_init();
 void HAL_init_board();
+
+//
+// Delay in cycles (used by DELAY_NS / DELAY_US)
+//
+FORCE_INLINE static void DELAY_CYCLES(uint32_t x) {
+  unsigned long start, ccount, stop;
+
+  /**
+   * It's important to care for race conditions (and overflows) here.
+   * Race condition example: If `stop` calculates to being close to the upper boundary of
+   * `uint32_t` and if at the same time a longer loop interruption kicks in (e.g. due to other
+   * FreeRTOS tasks or interrupts), `ccount` might overflow (and therefore be below `stop` again)
+   * without the loop ever being able to notice that `ccount` had already been above `stop` once
+   * (and that therefore the number of cycles to delay has already passed).
+   * As DELAY_CYCLES (through DELAY_NS / DELAY_US) is used by software SPI bit banging to drive
+   * LCDs and therefore might be called very, very often, this seemingly improbable situation did
+   * actually happen in reality. It resulted in apparently random print pauses of ~17.9 seconds
+   * (0x100000000 / 240 MHz) or multiples thereof, essentially ruining the current print by causing
+   * large blobs of filament.
+   */
+
+  __asm__ __volatile__ ( "rsr     %0, ccount" : "=a" (start) );
+  stop = start + x;
+  ccount = start;
+
+  if (stop >= start) {
+    // no overflow, so only loop while in between start and stop:
+    // 0x00000000 -----------------start****stop-- 0xffffffff
+    while (ccount >= start && ccount < stop) {
+      __asm__ __volatile__ ( "rsr     %0, ccount" : "=a" (ccount) );
+    }
+  }
+  else {
+    // stop did overflow, so only loop while outside of stop and start:
+    // 0x00000000 **stop-------------------start** 0xffffffff
+    while (ccount >= start || ccount < stop) {
+      __asm__ __volatile__ ( "rsr     %0, ccount" : "=a" (ccount) );
+    }
+  }
+
+}

Marlin/src/HAL/HAL_ESP32/Servo.cpp

@@ -37,7 +37,7 @@ Servo::Servo() {
 
 int8_t Servo::attach(const int inPin) {
   if (channel >= CHANNEL_MAX_NUM) return -1;
-  if (pin > 0) pin = inPin;
+  if (inPin > 0) pin = inPin;
 
   ledcSetup(channel, 50, 16); // channel X, 50 Hz, 16-bit depth
   ledcAttachPin(pin, channel);

Marlin/src/HAL/shared/Delay.h

@@ -145,21 +145,7 @@
   }
   #undef nop
 
-#elif defined(ESP32)
-
-  FORCE_INLINE static void DELAY_CYCLES(uint32_t x) {
-    unsigned long ccount, stop;
-
-    __asm__ __volatile__ ( "rsr     %0, ccount" : "=a" (ccount) );
-
-    stop = ccount + x; // This can overflow
-
-    while (ccount < stop) { // This doesn't deal with overflows
-      __asm__ __volatile__ ( "rsr     %0, ccount" : "=a" (ccount) );
-    }
-  }
-
-#elif defined(__PLAT_LINUX__)
+#elif defined(__PLAT_LINUX__) || defined(ESP32)
 
   // specified inside platform