MicroPython i2c `writeto()` fails for unknown reason

[jmdevy]

Hi,

I'm trying to use MicroPython's i2c in the emulator (docs) through direct use of the rp2040js library

The following code fails when executed in the emulator:

import machine
sda = machine.Pin(16)
scl = machine.Pin(17)
i2c = machine.I2C(0, sda=sda, scl=scl, freq=1000000)
packet = bytearray(2)
addr = 0x3C
packet[0] = 0x80
packet[1] = 0x10
i2c.writeto(addr, packet)

Output (including lines entered and echoed from REPL):

>>> import machine
>>> sda=machine.Pin(16)
>>> scl=machine.Pin(17)
>>> i2c = machine.I2C(0, sda=sda, scl=scl, freq=1000000)
>>> packet = bytearray(2)
>>> addr = 0x3C
>>> packet[0] = 0x80
>>> packet[1] = 0x10
>>> i2c.writeto(addr, packet)
Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
OSError: [Errno 5] EIO

However, writevto() seems to work without error but I can't find a way to receive/intercept the data transmitted from i2c, for example:

mcu.i2c[0].onStart = () => {
  console.log("I2C Start");
}

mcu.i2c[0].onStop = () => {
  console.log("I2C Stop");
}

mcu.i2c[0].onConnect = () => {
  console.log("I2C Connect");
}

mcu.i2c[0].onReadByte = () => {
  console.log("R");
}

mcu.i2c[0].onWriteByte = () => {
  console.log("W");
}

The above only shows that i2c starts but none of the other callbacks fire, in any case, it doesn't look like I would be able to intercept the data in JS using the above callbacks, is there any way?

[urish]

The thing is, you need to tell the i2c peripheral to complete each operation, e.g.:

const i2c = mcu.i2c[0];
i2c.onStart = () => {
  console.log("I2C Start");
  // now tell I2C that we're done:
  i2c.completeStart();
}

You can find the complete list of "complete" methods in the i2c peripheral's source code.