// GPIO toggle test — ATSAMD11C14A, NO_BOOTLOADER, CMSIS-DAP
// Proves firmware is running when no LED is available
// Probe GND ↔ TEST_PIN with multimeter: should read 3.3V → 0V on 5s cycle

#define TEST_PIN 5   // A5 — available pad, not used by OLED or touch

void setup() {
  pinMode(TEST_PIN, OUTPUT);
}

void loop() {
  digitalWrite(TEST_PIN, HIGH);   // multimeter reads: 3.3V
  delay(5000);
  digitalWrite(TEST_PIN, LOW);    // multimeter reads: 0V
  delay(5000);
}