Wire library - Slave hang

[tetsudou]

Hi all!

I have a rather weird bug going on in my I2C installation. I have several (8) ATTiny1604 slaves connected to an Arduino Nano master. Three of them run Code A and the rest run Code B (the difference is the peripheral it drives). What happens is that randomly, when the master is attempting to contact B-type slaves, one of these slaves would cut out after receiving the R/W bit and pull both SDA and SCL low as shown in the picture (yellow = SCL, purple = SDA). It would then proceed to completely hang, blocking the bus.

I am using external pull-ups (560 Ohm to ensure sharp edges).

If only A-type slaves are contacted (even with B-type slaves on the line), the code runs fine indefinitely (at least for a couple of hours). If at least one slave running Code B is contacted, it invariably eventually causes the line to cut out.

I have tried versions 2.3.2, 2.4.2 and 2.4.3 of the core. On the former two, the failure happens after some time (after 50-70 messages). On the latter, it always happens on the first or the second message.

What could be the reason for this behaviour?

Thanks in advance!

Code_A.ino:

#include <Wire.h>
#include <Servo_megaTinyCore.h>

Servo myservo;

int address = 2;//different for each slave

int pos = 42;
int servoPin = 10;
int lightPin = 1;
int lstate = 1;
int px = 1;
int x = 0;
char message[10];
boolean action = true;

void setup() {
  for (int i = 0; i < 10; i++) {
    message[i] = '0';
  }
  delay(2000);
  pinMode(lightPin, OUTPUT);
  digitalWrite(lightPin, 1);
  myservo.attach(servoPin);
  myservo.write(42);
  while (pos > 15) { //15
    pos--;
    myservo.write(pos);
    delay(10);
  }
  myservo.detach();
  Wire.setClock(100000);
  Wire.begin(address);                // join i2c bus with address #8
  Wire.onReceive(receiveEvent); // register event
  //Serial.begin(9600);           // start serial for output
}

void loop() {
  if (px == 1) digitalWrite(lightPin, lstate);
  else digitalWrite(lightPin, lstate);
  if (px != x) {
    myservo.attach(servoPin);
    if (x == 1) {
      while (pos < 75) { //75
        pos++;
        myservo.write(pos);
        delay(10);
      }
    }
    else if (x == 0) {
      while (pos > 15) { //15
        pos--;
        myservo.write(pos);
        delay(10);
      }
    }
    myservo.detach();
    px = x;
  }
}

// function that executes whenever data is received from master
// this function is registered as an event, see setup()
void receiveEvent(int howMany) {
  int i = 0;
  while (0 < Wire.available()) { // loop through all but the last
    char c = Wire.read(); // receive byte as a character
    message[i] = c;
    i++;
  }
  if (message[0] == 'l') {
    if (message[1] == 0) digitalWrite(lightPin, 0);
    else if (message[1] == 1) digitalWrite(lightPin, 0);
    lstate = message[1];
  }
  else if (message[0] == 's') {
    x = message[1];
  }
}

Code_B.ino:

#include <Wire.h>

int address = 8;//different for each slave

int red = 10;//Red: C = 30uF
int amb = 8;//Amber: C = 30uF
int grn = 0;//Green: C = 2uF
int call = 1;//same as yellow
int red2 = 9;//Red: C = 30uF
int amb2 = 4;//Amber: C = 30uF
int grn2 = 2;//Green: C = 2uF
int call2 = 3;
char message[10];
boolean action = false;

void setup() {
  delay(1000);
  for (int i = 0; i < 10; i++) {
    message[i] = '0';
  }
  pinMode(red, OUTPUT);
  digitalWrite(red, HIGH);
  pinMode(red2, OUTPUT);
  digitalWrite(red2, HIGH);
  Wire.setClock(100000);
  TWI0.SADDR = address;
  Wire.begin(address);                // join i2c bus with address #8
  Wire.onReceive(receiveEvent); // register event
}

void loop() {
  pinMode(red, OUTPUT);
  digitalWrite(red, HIGH);
  delay(500);
  pinMode(red, INPUT);
  digitalWrite(call, LOW);
  delay(500);
}

// function that executes whenever data is received from master
// this function is registered as an event, see setup()
void receiveEvent(int howMany) {
  int i = 0;
  while (0 < Wire.available()) { // loop through all but the last
    char c = Wire.read(); // receive byte as a character
    message[i] = c;
    i++;
  }
  //if (message[0] == '1') {
  if (message[0] == '1') {
    digitalWrite(grn, LOW);
    pinMode(grn, INPUT);
    digitalWrite(amb, LOW);
    pinMode(amb, INPUT);
    digitalWrite(call, LOW);
    pinMode(call, INPUT);
    delay(300);
    pinMode(red, OUTPUT);
    digitalWrite(red, HIGH);
  }
  else if (message[0] == '2') {
    digitalWrite(grn, LOW);
    pinMode(grn, INPUT);
    digitalWrite(amb, LOW);
    pinMode(amb, INPUT);
    delay(300);
    pinMode(red, OUTPUT);
    digitalWrite(red, HIGH);
    pinMode(call, OUTPUT);
    digitalWrite(call, HIGH);
  }
  else if (message[0] == '3') {
    digitalWrite(grn, LOW);
    pinMode(grn, INPUT);
    digitalWrite(red, LOW);
    pinMode(red, INPUT);
    digitalWrite(call, LOW);
    pinMode(call, INPUT);
    delay(300);
    pinMode(amb, OUTPUT);
    digitalWrite(amb, HIGH);
  }
  else if (message[0] == '4') {
    digitalWrite(amb, LOW);
    pinMode(amb, INPUT);
    digitalWrite(red, LOW);
    pinMode(red, INPUT);
    digitalWrite(call, LOW);
    pinMode(call, INPUT);
    delay(300);
    pinMode(grn, OUTPUT);
    digitalWrite(grn, HIGH);
  }
  //}
  //else if (message[0] == '2') {
  else if (message[0] == '5') {
    digitalWrite(grn2, LOW);
    pinMode(grn2, INPUT);
    digitalWrite(amb2, LOW);
    pinMode(amb2, INPUT);
    digitalWrite(call2, LOW);
    pinMode(call2, INPUT);
    delay(300);
    pinMode(red2, OUTPUT);
    digitalWrite(red2, HIGH);
  }
  else if (message[0] == '6') {
    digitalWrite(grn2, LOW);
    pinMode(grn2, INPUT);
    digitalWrite(amb2, LOW);
    pinMode(amb2, INPUT);
    delay(300);
    pinMode(red2, OUTPUT);
    digitalWrite(red2, HIGH);
    pinMode(call2, OUTPUT);
    digitalWrite(call2, HIGH);
  }
  else if (message[0] == '7') {
    digitalWrite(grn2, LOW);
    pinMode(grn2, INPUT);
    digitalWrite(red2, LOW);
    pinMode(red2, INPUT);
    digitalWrite(call2, LOW);
    pinMode(call2, INPUT);
    delay(300);
    pinMode(amb2, OUTPUT);
    digitalWrite(amb2, HIGH);
  }
  else if (message[0] == '8') {
    digitalWrite(amb2, LOW);
    pinMode(amb2, INPUT);
    digitalWrite(red2, LOW);
    pinMode(red2, INPUT);
    digitalWrite(call2, LOW);
    pinMode(call2, INPUT);
    delay(300);
    pinMode(grn2, OUTPUT);
    digitalWrite(grn2, HIGH);
  }
  //}
}