How to avoid I2C bus stuck after a board reset

[cparata]

I noticed that sometimes if you reset the board during an I2C transaction the I2C bus remains stuck.
A possible solution that I found is to send a bit-banged STOP sequence before the I2C begin. Maybe it would be better to include this procedure in the Wire begin implementation or in a dedicated Wire API to improve the stability of the library.
You can find below the bit-banged STOP sequence that normally I send to unlock the I2C bus before the I2C begin:

pinMode(SCL_PIN, OUTPUT);
pinMode(SDA_PIN, OUTPUT);

for (int i = 0; i<10; i++) {
  digitalWrite(SDA_PIN, LOW);
  delay(3);
  digitalWrite(SCL_PIN, HIGH);
  delay(3);
  digitalWrite(SDA_PIN, HIGH);
  delay(3);
  digitalWrite(SCL_PIN, LOW);
  delay(3);
}

pinMode(SDA_PIN, INPUT);
pinMode(SCL_PIN, INPUT);

Best Regards,
Carlo

[ABOSTM]

Hi Carlo, thanks for this sharing.
Any reason to send STOP 10 times in loop ?

[cparata]

Hi @ABOSTM ,
nothing in particular. I just try to send the "STOP" sequence 10 times to be sure that all the devices on the I2C bus are able to "see" it. Sometimes the devices take some time to be alive on the bus. But it is just an example. Maybe we can reduce the number of loops.
Best Regards,
Carlo

[cparata]

Hi all,
I found also this implementation on the web:

https://www.forward.com.au/pfod/ArduinoProgramming/I2C_ClearBus/I2C_ClearBus.ino.txt

The implementation is described in this article:

https://github-wiki-see.page/m/Koepel/How-to-use-the-Arduino-Wire-library/wiki/How-to-unlock-a-stuck-I2C-bus

They suggest to do 20 clock loops (> 16) to address also devices that manage 16 bits registers. Besides they do not advice to put high the SDA and SCL because I2C bus is open collector