XIAO_ESP32C3 Serial.print() excution time depend on serial monitor ON/OFF

msfujino · December 14, 2022, 6:44am

There is a large difference in the execution time of Serial.print() depending on whether the serial monitor is turned on/off, and I cannot find the cause. You can check it in the following sketch.
Turn on the LED for 10mS for the execution time of Serial.print() + visibility of the LED. When the serial monitor is on, ON 10mS/OFF 100mS is repeated, but when the serial monitor is off, the execution time of Serial.print() becomes 400mS and ON 400mS/OFF 100mS is repeated.
Can this phenomenon be reproduced?
I need help.

void setup() {
  Serial.begin(115200); 
  pinMode(D10, OUTPUT); // LED 
}

void loop() {
  digitalWrite(D10, HIGH);        // LED ON  
  Serial.println("serial print"); // print to serial monitor
  delay(10);                      // 10mS For LED visibility
  digitalWrite(D10, LOW);         // LED OFF

  // if serial monitor off, LED blink long time(about 400mS)
  // if serial monitor on, LED blink short time(about 10mS) 
  
  delay(100);                     // OFF 100mS and loop
}

PJ_Glasso · December 14, 2022, 3:48pm

seasons Greetings @ms, Have you tried
changing the Baud Rate, may yield a different result.
have you tried 9600 ?
is it different using millis instead?
definitely strange behavior.
GL

msfujino · December 14, 2022, 10:15pm

Hi PJ_Glasso,
Of course I have tried 9600 and timers using millis() instead of delay() to no avail. I only have one XIAO_ESP32C3 so I can’t confirm if there is a problem with my board. If it is possible, I would appreciate if someone could try it.

PJ_Glasso · December 14, 2022, 10:50pm

I try it, and Yes it does blink faster or slower Video
HTH
GL

msfujino · December 14, 2022, 11:22pm

Thanks for trying it.
I found a site that discusses the same issue, it seems to be specific to the ESP32C3. I am reading the comments now.
If I find out anything I will post it.

github.com/espressif/arduino-esp32

ESP32C3M1: Serial.print() calls when not connected to USB cause delays.

opened 07:01AM - 14 Jul 22 UTC

closed 10:47AM - 14 Dec 22 UTC

mahboud

Area: Performance Area: Peripherals API

### Board ESP32C3M1 ### Device Description Custom board: ![IMG_7922](https:/…/user-images.githubusercontent.com/1689095/178842464-984ba4ec-f087-458f-8de0-589a38dd1681.jpeg) ### Hardware Configuration GPIO 18 & 19 are connected to USB. USB is used to program the device and to monitor Serial.print output. ### Version v2.0.3 ### IDE Name Arduino ### Operating System MacOS 10.15.7 ### Flash frequency 40Mhz ### PSRAM enabled yes ### Upload speed 115200 ### Description USB is used to program the device and to monitor Serial.print output. However, when the device is unplugged, and the Serial.print() lines are left in the code, they cause delays of a second or so. Plugging back in will make the delays go away. If I remove the Serial.print() lines, it makes the delays disappear too. ### Sketch ```cpp #include <Wire.h> #include <Adafruit_NeoPixel.h> #define LED_PIN 6 #define NEOPIXEL_PIN LED_PIN Adafruit_NeoPixel pixels(1, NEOPIXEL_PIN, NEO_GRB + NEO_KHZ800); void setup() { // put your setup code here, to run once: Serial.begin(115200); } void loop() { // put your main code here, to run repeatedly: pixels.begin(); // INITIALIZE NeoPixel strip object (REQUIRED) Serial.print("Red... "); // drawMessage("Test Red LED"); pixels.setPixelColor(0, pixels.Color(64, 0, 0)); pixels.show(); delay(500); Serial.print("Green... "); // drawMessage("Test Green LED"); pixels.setPixelColor(0, pixels.Color(0, 64, 0)); pixels.show(); delay(500); Serial.print("Blue... "); // drawMessage("Test Blue LED"); pixels.setPixelColor(0, pixels.Color(0, 0, 64)); pixels.show(); delay(500); Serial.print("White... "); // drawMessage("Test Whitish LED"); pixels.setPixelColor(0, pixels.Color(64, 64, 64)); pixels.show(); delay(500); Serial.print("Off... "); pixels.clear(); pixels.show(); delay(500); Serial.println("Done. Looping"); }``` ``` ### Debug Message ```plain There is no debug or error message. ``` ### Other Steps to Reproduce Run the sketch. While the device is plugged into a computer with Arduino, the lights flash faster. When you unplug the USB cable the lights slow down. With more or longer Serial.print output, the delay can be more than a second. That same code above is running on the two boards in this video. When you plug the USB in, you can see that the flash rate increases on the one plugged in. https://user-images.githubusercontent.com/1689095/178857842-551736c3-3ac0-4adc-9bf8-758c5a6fa6ad.mov ### I have checked existing issues, online documentation and the Troubleshooting Guide - [X] I confirm I have checked existing issues, online documentation and Troubleshooting guide.

msfujino · December 15, 2022, 4:37am

I added “Serial.setTxTimeoutMs(0);” according to the comments in the link below and that solved the problem.
“ESP32C3M1: Serial.print() calls when not connected to USB cause delays. · Issue #6983 · espressif/arduino-esp32 · GitHub”

cgwaltney · July 13, 2023, 2:09pm

This is a real thing

i began working with a XIOA and GPS program that was originally built with a
XIAO SAMD i got a XIAO ESP32C3 and was trying to send the GPS thru wifi
and noticed lots of lag and problems and differences between the activity of the
serial connection between the boards