I2C scan takes extremely long (~126 seconds) with Wire.endTransmission() on empty bus #492
Description
Board/Environment
Board: Arduino Uno R4 WiFi
Core Version: 1.5.1
IDE: Arduino IDE 2.2.1
OS: Windows
Sketch to reproduce
#include <Wire.h>
void setup() {
Wire.begin();
Serial.begin(115200);
delay(1000);
Serial.println("\nI2C Scanner with Timing");
}
void loop() {
byte error;
unsigned long startTime = millis();
Serial.println("Scanning...");
for (byte address = 1; address < 127; address++) {
Wire.beginTransmission(address);
error = Wire.endTransmission();
}
unsigned long elapsed = millis() - startTime;
Serial.print("Time taken to scan I2C bus 0: ");
Serial.print(elapsed);
Serial.println(" ms");
delay(5000);
}Observed Behavior
With no I²C devices connected, a single full scan takes ~126,000 ms (≈126 seconds).
Expected scan duration is typically <200 ms on other Arduino cores.
Each Wire.endTransmission() seems to block for ~1 second when no device responds.
Expected Behavior
A complete scan of addresses 1–126 should complete in a few hundred milliseconds, even when no devices are present.