A test harness, using an UNO/ESP8266, for the ATtiny85 hardware watchdog, targeting D1M Blocks (custom shields for Wermos D1 Mini)

uno_test_hardware_watchdog.ino

#include <Wire.h>

byte _interval = 0;

void setup() {
  Serial.begin(9600);
  Wire.begin(); // join i2c bus (address optional for master)
  delay(3000);
  Serial.println("Sending started");
  SendCmd('G', 1); // get the expected pat interval
  Serial.print("The Interval on the ATTINY85 is ");
  Serial.print(_interval);
  Serial.println( " seconds");
}

byte x = 1;

void loop() {
  if (x < 5){
    Serial.print("Patting the dog #");
    Serial.println(x);
    SendCmd('P', 0);
  }else{
     Serial.println("Stopped patting the dog, expect a reset");
  }
  x++;
  delay(10000);
}

void SendCmd(char cmd, byte par) {
  Wire.beginTransmission(8); // transmit to device #8
  Wire.write(cmd);           // sends a char
  Wire.write(par);             // sends one byte
  Wire.endTransmission();
  if (cmd == 'G'){// we are only getting Interval
    Wire.requestFrom(8,1);    // request a single byte from slave device #25
    while(Wire.available())    // slave may send less than requested
    { 
      _interval = Wire.read();    // receive a byte as character
    }
  }
  Serial.print(String(cmd) + " : ");
  Serial.println(par);
}