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Feather M4 + BNO085 I/O error
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Please be positive and constructive with your questions and comments.

Re: Feather M4 + BNO085 I/O error

by askker on Fri Sep 10, 2021 8:24 pm

gammaburst wrote:Hi askker,

Short answer: Install an additional pullup resistor, around 2K to 3K ohms, from SDA to 3.3V. Leave SCL alone. Your project will probably now run reliably.

Long answer: Your SDA/SCL touch-test results agree with mine. Your project, and every other BNO08X and BNO055 project, are on the verge of failure due to an I2C hardware timing bug in the BNO08X (and BNO055). During an I2C clock-stretching bus cycle, the bug occasionally causes violation of the SDA-high to SCL-high setup time, and if that violation is sufficiently large then the I2C transfer will fail. If you slow down SDA's rise time by a few nanoseconds (by grabbing it with your finger), the timing error worsens and your I2C transfer fails. If you slow down SCL's rise time by a few nanoseconds (by grabbing it with your finger), the timing error reduces and your I2C transfer works more reliably. Adding the aforementioned pullup resistor speeds-up SDA's risetime by many nanoseconds, and although that's insufficient to eliminate the timing error, it reduces the error sufficiently to avoid failure in all the projects that I've seen.

Those are my opinions and experiences. Corrections are welcome.


Amazing, I added a 2.5K ohm pullup resistor and now it's working like a charm. Can comfirm to work on all 5 computers and touching the SDA no longer crashes the code.

askker
 
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Re: Feather M4 + BNO085 I/O error

by gammaburst on Sat Sep 11, 2021 11:51 am

Thank you askker for your feedback.
At long last, you're the first!

gammaburst
 
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Joined: Thu Dec 31, 2015 12:06 pm

Please be positive and constructive with your questions and comments.