OSError: [Errno 5] EIO

[Mathemmagician]

Posting here mainly for visibility as the solution is provided below.

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When running bno_test.py, I sometimes get

Traceback (most recent call last):
  File "<stdin>", line 44, in <module>
  File "bno055_base.py", line 86, in <lambda>
  File "bno055_base.py", line 118, in scaled_tuple
  File "bno055_base.py", line 200, in _readn
OSError: [Errno 5] EIO

Which I was able to resolve by reducing the frequency, i.e.

before: i2c = machine.I2C(1, sda=machine.Pin(14), scl=machine.Pin(15))
after: i2c = machine.I2C(1, sda=machine.Pin(14), scl=machine.Pin(15), freq=5000)

[peterhinch]

This can be caused by pullup resistors with too high a value or wires too long.

[Mathemmagician]

Interesting. My wires are very short, and the pull-up resistors are built it. Using Adaftuit's https://www.adafruit.com/product/2472

[peterhinch]

I'm baffled. I used the same breakout in my testing and in many hours of work developing a Quaternion class and never saw this error.

In general I2C interfaces which work at low clock rates but not at higher ones are often the result of capacitive loading, which can be countered by lower value pulups. The Adafruit pullups are 10KΩ which is rather high, you might try adding pullups to 3.3V in the region of 1KΩ to 2KΩ. But this is clutching at straws, I never found a need.