Errors and troubleshooting

On this page, you find the cause and the fix for errors that come up during setup, compiling and a match with Probot Core.

The page describes probot-core 0.3.0. Probot Blocks also generates 0.3.0 code. First check the status indicators, then find the heading for your symptom. If a message appeared on the screen, the headings start with that message.

Check the status indicators first

The status LED on the top of the board shows the robot's current state. The library controls its color. You cannot change it from your code. The Driver Station also shows some states with a message that covers the whole screen.

For all LED colors and the extra signal lamp (RSL), see Use the status LED.

Installation and upload

Arduino IDE writes the error in the output panel at the bottom. For the setup steps, see Set up Arduino IDE for Probot.

Port list is empty or the upload fails

The Tools > Port list stays empty, or the upload stops with a port error.

"Sketch too big"

Cause: The code does not fit in the application area of the default partitioning (Partition Scheme). The library uses about three quarters of this area. Large code runs out of space.

Fix: In Tools > Partition Scheme, select Huge APP (3MB No OTA/1MB SPIFFS), and upload again. When you open a new sketch or select the board again, check this setting.

See Set up Arduino IDE for Probot.

"probot.h: No such file or directory"

Cause: The probot library is not installed.

Fix: Select Tools > Manage Libraries, type probot, and press Install.

"Adafruit_NeoPixel.h: No such file or directory"

Cause: The Adafruit NeoPixel library, which drives the status LED, is not installed. probot depends on this library.

Fix: In Manage Libraries, type adafruit neopixel, and install it. If the IDE asks about dependencies when you install probot, press Install all.

Compile errors

These errors come from the settings in your code. The compile stops, and nothing is uploaded to the board.

"PROBOT_WIFI_AP_PASSWORD must be at least 8 characters."

If the password macro is missing, or you wrote it after the #include line, the message is:

Driver station AP password not provided. Define PROBOT_WIFI_AP_PASSWORD (>=8 chars) before including probot.h.

Cause: The robot's WiFi network does not open without a password. The password must have at least 8 characters.

Fix: Write the password before #include <probot.h>, with at least 8 characters:

#define PROBOT_WIFI_AP_SSID     "Probot"
#define PROBOT_WIFI_AP_PASSWORD "Probot1234"   // at least 8 characters
#define PROBOT_WIFI_AP_CHANNEL  1             // 1-13
#include <probot.h>

See Set up the robot's WiFi.

"PROBOT_WIFI_AP_CHANNEL must be 1-13."

The full message is: "PROBOT_WIFI_AP_CHANNEL must be 1-13. To auto-pick the channel at boot, set PROBOT_WIFI_AUTO_CHANNEL 1 (single-robot use only)."

If the channel macro is missing, the message is:

WiFi AP channel not provided. Define PROBOT_WIFI_AP_CHANNEL (1-13) before including probot.h.

Cause: The 2.4 GHz channel that the robot broadcasts on must be known at compile time. PROBOT_WIFI_AP_CHANNEL is missing, or it is outside 1-13.

Fix: Write a channel from 1 to 13, for example #define PROBOT_WIFI_AP_CHANNEL 1. If several robots are in the same hall, give each robot a different channel from 1, 5, 9 and 13.

See Improve the signal quality.

"PROBOT_WIFI_AP_SSID must be 25 characters or fewer when MAC suffix is enabled."

Two more messages can appear under this heading:

PROBOT_WIFI_AP_SSID must be 32 characters or fewer.
PROBOT_WIFI_AP_SSID must be at least 1 character.

Cause: The network name (SSID) can have at most 32 characters. When PROBOT_WIFI_AP_SSID_MAC_SUFFIX is defined, the library adds a 7-character suffix, -XXXXXX, to the end of the name. So the name can have at most 25 characters. If you do not write a network name at all, the name is Probot and the suffix turns on by itself.

Fix: Shorten the network name. With the suffix on, write at most 25 characters. With the suffix off, write at most 32 characters. Do not write an empty name ("").

"undefined reference to `robotEnd()'"

The compile step passes. The build stops at the link step. The name changes with the missing function: robotInit(), teleopInit(), teleopLoop(), autonomousInit() or autonomousLoop().

Cause: In 0.3.0, all six functions are required. If one is missing, the code does not link.

Fix: Write all six functions. Each body can be empty. The shortest correct skeleton:

#define PROBOT_WIFI_AP_SSID     "Probot"
#define PROBOT_WIFI_AP_PASSWORD "Probot1234"   // at least 8 characters
#define PROBOT_WIFI_AP_CHANNEL  1             // 1-13
#include <probot.h>

void robotInit() {}        // once, when you press Init
void robotEnd() {}         // once, at Stop: stop the motors here
void teleopInit() {}       // once, when TeleOp starts
void teleopLoop() {}       // called again and again during TeleOp
void autonomousInit() {}   // once, when autonomous starts
void autonomousLoop() {}   // called again and again during autonomous

See Write the functions for the match flow.

"redefinition of 'void setup()'"

The same message appears for loop(): "redefinition of 'void loop()'".

Cause: The library owns setup() and loop(). It defines both in probot.h. If your code defines them again, the compiler stops.

Fix: Delete the setup() and loop() functions from your code. Move the code that runs at startup to robotInit(). Move the code that repeats to teleopLoop() or autonomousLoop().

See Write the functions for the match flow.

Connection and gamepad

The interface does not open, or "Another client is already connected."

The robot accepts one device at a time. The device that opens the interface first owns it. The other devices see this message (HTTP 403).

See Driver Station interface.

Gamepad "Not Connected"

In the Driver Station, the gamepad status says "Not Connected", or the axis values never change.

Servo jitters

The servo does not hold its position. It twitches now and then, or it moves without a command.

See Drive the servo.

During a match

LED blinks red: loop stalled

The Driver Station's Telemetry panel shows this line. In the Logs tab, Deadline Miss shows "YES".

!! LOOP STALLED — inputs zeroed, holding safe (no reboot)

Cause: teleopLoop() or autonomousLoop() did not finish in 2 seconds. This time is the PROBOT_LOOP_DEADLINE_MS macro (default 2000 ms).

The library resets the gamepad inputs and turns the LED red. It does not stop your task, and it does not restart the board. The phase does not change: autonomous stays in autonomous, and TeleOp stays in TeleOp. The error clears by itself when the pass ends.

If you cannot find the cause, simplify the loop step by step: Narrow down the problem step by step.

"EMERGENCY STOPPED"

A message covers the Driver Station, and a Reboot Robot button appears below it. The LED turns red and stays red.

EMERGENCY STOPPED
Robot disabled — reboot required to clear

The Telemetry panel and the Serial Monitor show these lines:

!! EMERGENCY STOP — robot disabled, reboot required
[SYS  ] EMERGENCY STOP

Cause: EMERGENCY STOP was pressed in the Driver Station, or your code called probot::emergencyStop(). This is a safety behavior, not a fault. The library stops your task, runs robotEnd() once, and drives the PROBOT_ESTOP_ENABLE_PIN LOW if you defined it. Until the robot restarts, it rejects all commands except EMERGENCY STOP and Reboot Robot (HTTP 409).

Fix: Only a restart clears the lock. Press Reboot Robot, or turn the robot's power off and on. Then press Init and Start again.

"DISCONNECTED": connection lost, robot stopped

The Driver Station shows "DISCONNECTED" and "Trying to reconnect..." over the screen. The Serial Monitor shows a line that starts with "DS timeout: no activity for". The library also writes this line to the Telemetry panel:

!! DS CONNECTION LOST — stopping robot

When the connection drops, the library does these steps in order:

1. If no gamepad data arrives for 500 ms, the axes and buttons read as zero (PROBOT_INPUT_TIMEOUT_MS).
2. If the owner device stays silent for 5 seconds, ownership is released, and the gamepad data is reset (PROBOT_DS_OWNER_TIMEOUT_MS).
3. If the Driver Station stays silent for 10 seconds, the robot stops and robotEnd() runs (PROBOT_DS_TIMEOUT_MS).

When the connection comes back, the robot does not start by itself. Press Init and Start again.

See Improve the signal quality.

Connection lost, robot did not stop

The Telemetry panel shows this line:

!! DS CONNECTION LOST — joystick neutral, waiting reconnect

Cause: The code has #define PROBOT_DS_TIMEOUT_FORCE_STOP 0. With this setting, the robot does not stop after 10 seconds of silence. The gamepad data reads as zero, and teleopLoop() or autonomousLoop() keeps running. When the connection comes back, the robot continues from where it was.

Fix: If you chose this setting, the behavior is expected. Autonomous also keeps running during this time. If you do not want the robot to move without a connection, delete the macro (the default is 1). For the causes of a drop, see Connection lost, robot stopped.

Robot restarted after an emergency stop

The Serial Monitor shows this line:

[SYS  ] estop robotEnd timed out -> restart

Cause: During an emergency stop, robotEnd() did not finish in 500 ms (PROBOT_ESTOP_END_MS). Instead of waiting, the library restarts the board. An emergency stop interrupts your task in the middle of its work. That is why an I2C call inside robotEnd() can also stall.

Fix: Keep robotEnd() short. Reset the motor pins, and return. Do not put delay(), a long loop or an I2C call without a timeout inside it.

Motors do not stop after Stop

At Stop, the library calls robotEnd(). Stopping the motors is your code's job. robotEnd() runs after the current loop pass ends.

An example with one motor and a BTS7960-style driver:

#define PROBOT_WIFI_AP_SSID     "Probot"
#define PROBOT_WIFI_AP_PASSWORD "Probot1234"   // at least 8 characters
#define PROBOT_WIFI_AP_CHANNEL  1
#include <probot.h>

// Change the pins for your board
#define MOTOR_RPWM 5   // forward
#define MOTOR_LPWM 6   // backward

void motorSur(float guc) {
  int duty = (int)(fabsf(guc) * 255.0f);
  if (duty > 255) duty = 255;
  if (guc > 0.02f)       { analogWrite(MOTOR_RPWM, duty); analogWrite(MOTOR_LPWM, 0); }
  else if (guc < -0.02f) { analogWrite(MOTOR_RPWM, 0);    analogWrite(MOTOR_LPWM, duty); }
  else                   { analogWrite(MOTOR_RPWM, 0);    analogWrite(MOTOR_LPWM, 0); }
}

void robotInit() {
  pinMode(MOTOR_RPWM, OUTPUT);
  pinMode(MOTOR_LPWM, OUTPUT);
  motorSur(0);
}

void robotEnd() {
  motorSur(0);   // The motor stops at Stop
}

void teleopInit() {}

void teleopLoop() {
  auto js = probot::io::joystick_api::makeDefault();
  motorSur(js.getLeftY());   // left stick forward: motor forward
}

void autonomousInit() {}
void autonomousLoop() {}

See Drive the motor.

Report a bug

If this page has no fix for an error, report it on the library's GitHub page: github.com/probot-studio/probot-core/issues.

Include these in your message:

• The shortest code that shows the error.
• The last button you pressed (for example Init or Start).
• The text on the screen, in the Telemetry panel, or in the Serial Monitor, word for word.
• The library version (0.3.0) and the browser you use.