Adafruit_blinka with I2C3 on raspberry pi 4 Moderators: adafruit_support_bill, adafruit

[ChrisJerome]

Hi,

The i2c clock stretching bug is fixed on RPi4 by enabling I2C-3. This is great news because I would like to use BNO055 with the RPi over I2C. I have I2C-3 enabled and I have installed adafruit_blinka, but when I run blinkatest.py I get the error RuntimeError: I2C Bus #1 not found...

Is there a way to get adafruit_blinka to work with I2C-3 on RPi4? I've tried modifying the line i2c = busio.I2C(board.SCL, board.SDA) to i2c = busio.I2C(board.SCL3, board.SDA3), but that was ineffective.

Thanks!

[adafruit_support_mike]

Hmm.. I haven't heard of an I2C-3 channel, but would guess that enabling it disables I2C-1.

I don't think there's any code support for that in Blinka, and will have to check with the folks who handle that code to see if it's possible to make it work with the code in its current state.

[ChrisJerome]

I haven't found much documentation, except this:

Re: Raspberry Pi 4 Thread - general discussion
• Quote
Sun Sep 29, 2019 10:00 am
jcyr wrote: ↑
Sun Sep 29, 2019 12:44 am
jdb wrote: ↑
Wed Sep 11, 2019 1:38 pm
Can you try using i2c3 on GPIO2&3?
In config.txt comment out dtparam=i2c_arm=on and add the line dtoverlay=i2c3,pins_2_3 . The corresponding device node is /dev/i2c-3.
Yes, clock stretching seems to work correctly on IC2-3.

From <https://www.raspberrypi.org/forums/viewtopic.php?p=1547115>

As you will see this disables I2C-1 and uses the same pins. However it appears there are multiple I2C channels available on RPi4, and they don't all use pins 2 and 3. I don't know if the clock stretching bug is fixed on any except IC2-3

[adafruit_support_mike]

I've passed the information along to the folks who handle the Blinka CircuitPython code for the RasPi. They'll check it out, and work of getting I2C-3 support added to the system if it's valid.

[ChrisJerome]

Thanks!

Meanwhile, in case anyone else is trying this, I got the BNO055 working over I2C-3 with the older instructions for the Raspberry Pi/Beagle Bone Black. I configured the connection using:

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bno = BNO055.BNO055(i2c=3)

And I followed the instructions for using a bit-banged non-standard I2C channel shown here: viewtopic.php?t=114464. In particular, I had to modify BNO055.py as shown in the GitHub link.

[MakerMelissa]

ChrisJerome,

I have now added support for i2c-3 to Blinka. You can update to the latest version by typing:

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pip3 install --upgrade adafruit-blinka

Pins 2 and 3 are the same as SDA and SCL, so all you need to do is have i2c-3 enabled and it should work automatically.

Melissa

[ChrisJerome]

Awesome! Thank you!