robustness improvements for serial on esp32

* fix for serial port on esp32 V4 builds (see upstream wled#5501)
* check that SERIAL_MAXTIME_MILLIS is below the task watchdog trigger time
* pet esp32 watchdog once before massive reading of serial input (AdaLight/TPM2)

Author: softhack007

wled00/wled.cpp

@@ -482,8 +482,12 @@ void WLED::setup()
   WRITE_PERI_REG(RTC_CNTL_BROWN_OUT_REG, 0); //disable brownout detection
   #endif
 
-  #ifdef ARDUINO_ARCH_ESP32
-  pinMode(hardwareRX, INPUT_PULLDOWN); delay(1);        // suppress noise in case RX pin is floating (at low noise energy) - see issue #3128
+  #if defined(ARDUINO_ARCH_ESP32) && !defined(ARDUINO_USB_CDC_ON_BOOT)
+    #if ESP_IDF_VERSION_MAJOR > 3
+      gpio_pulldown_en((gpio_num_t)hardwareRX); // pinMode() routes GPIO through the GPIO matrix and detaches UART0 RX - use gpio_pulldown_en() instead. See upstream issue #5501
+    #else
+      pinMode(hardwareRX, INPUT_PULLDOWN); delay(1);        // suppress noise in case RX pin is floating (at low noise energy) - see issue #3128
+    #endif
   #endif
   #ifdef WLED_BOOTUPDELAY
   delay(WLED_BOOTUPDELAY); // delay to let voltage stabilize, helps with boot issues on some setups

wled00/wled_serial.cpp

@@ -2,6 +2,7 @@
 #ifdef ARDUINO_ARCH_ESP32
 #include "esp_ota_ops.h"
 #endif
+#include "sdkconfig.h"
 
 /*
  * Adalight and TPM2 handler
@@ -10,6 +11,17 @@
 #define SERIAL_MAXTIME_MILLIS 100 // to avoid blocking other activities, do not spend more than 100ms with continuous reading
 // at 115200 baud, 100ms is enough to send/receive 1280 chars
 
+#ifdef ARDUINO_ARCH_ESP32
+  // CONFIG_INT_WDT_TIMEOUT_MS = 300 = interrupt watchdog timeout in milliseconds
+  // CONFIG_TASK_WDT_TIMEOUT_S = 5   = idle task watchdog timeout in seconds
+  // CONFIG_ESP_TASK_WDT_TIMEOUT_S (new name)
+#ifdef CONFIG_ESP_TASK_WDT_TIMEOUT_S
+static_assert(SERIAL_MAXTIME_MILLIS < (CONFIG_ESP_TASK_WDT_TIMEOUT_S * 1000 - 2 * portTICK_PERIOD_MS), "SERIAL_MAXTIME_MILLIS must be shorter than the IDLE watchdog timeout.");
+#else // arduino-esp32 1.0.x uses CONFIG_TASK_WDT_TIMEOUT_S
+static_assert(SERIAL_MAXTIME_MILLIS < (CONFIG_TASK_WDT_TIMEOUT_S * 1000 - 2 * portTICK_PERIOD_MS), "SERIAL_MAXTIME_MILLIS must be shorter than the IDLE watchdog timeout.");
+#endif
+#endif
+
 enum class AdaState {
   Header_A,
   Header_d,
@@ -108,10 +120,12 @@ void handleSerial()
   static byte red   = 0x00;
   static byte green = 0x00;
 
+  if (Serial.available() > 0) delay(1); // pet the watchdog
+
   unsigned long startTime = millis();
   while ((Serial.available() > 0) && (millis() - startTime < SERIAL_MAXTIME_MILLIS))
   {
-    yield();
+    yield(); // useless on esp32
     byte next = Serial.peek();
     switch (state) {
       case AdaState::Header_A: