RasPi Pico: Often (but not always) Errno 19 on i2c writes

[ajsirota]

I'm sometimes getting "OSError: [Errno 19] Unsupported operation" when attempting to write to an i2c device (a SparkFun Serial LCD) using a RasPi Pico.

code.py:

import board
import busio

i2c = busio.I2C(board.GP17, board.GP16)

while not i2c.try_lock():
    print("i2c not locked, retrying...")

print(i2c.scan())
i2c.writeto(114, "|-") # Clear
i2c.writeto(114, "Hello world!") # Show some text. Error happens here.

The error appears to be happening on line 11, according to the output. Am I trying to send an illegal character? Or is it a bug in CircuitPython?

EDIT: Oh. I suppose I should say that I am running Adafruit CircuitPython 6.2.0-beta.2 on 2021-02-11; Raspberry Pi Pico with rp2040. I don't know why I didn't say that in my initial comment!

[dhalbert]

There are issues with some I2C devices. The I2C peripherals on the RP2040 do not allow zero-length writes, which are the typical way to do scanning. We are working on a workaround for that.

If you remove the i2c.scan(), does the problem go away?

[ajsirota]

Hmm. I commented out the scan call, and I now get the same error every time! I don't think the scan() is what's causing it.

[dhalbert]

Could you try some other I2C device? What is the part number of the serial LCD you are using?

[ajsirota]

The LCD is SparkFun ID LCD-14073, running firmware version 1.4. That one is now discontinued, but LCD-16397 and LCD-16396 are the same apart from the addition of a QT/Qwiic connector if you want to test yourself. Give me a bit to scrounge up another device.

[ajsirota]

I don't get the error at all using a 8x8 bicolor LED matrix backpack (Adafruit PID 902). I am using the adafruit_ht16k33 library and not writing raw bytes though.

[ajsirota]

Just tested it using the absolute newest build as of b19e7c9, and the error still happens.

[ajsirota]

Tested again as of 15615ef, and it still happens.

Sorry, but because I do not have an SWD debugger or a logic analyzer, I cannot help with anything requiring that.

[ajsirota]

Tested using bus_device, and it appears to hang when attempting to init the device, unless I pass in probe=False. Then it gives me the OSError I was getting before. Here's the code I'm using:

import board
import busio
from adafruit_bus_device import i2c_device

i2c = busio.I2C(board.GP17, board.GP16)

while not i2c.try_lock():
    pass # Interestingly, it doesn't work without locking the bus. bus_device examples don't seem to require this. 
print("i2c locked.")

lcd = i2c_device.I2CDevice(i2c, 114, False)
print("Device initted.")

lcd.write("|-") # Clear display
lcd.write("Hello, world!") # Print text
print("Text shown.")

[dhalbert]

Try using bitbangio.I2C() on absolute latest. I am still working on getting busio.I2C() to work.

[ajsirota]

bitbangio.I2C works perfectly, thank you.