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For reference:

  • I am using the latest release Pi OS Lite, Aug 2020 version.
  • I am developing an application using Pi4J.
  • I am referring to pins via this Pinout: Pin Numbering - Raspberry Pi 3B+

I am using both I2C buses, 0 and 1, in my application. To enable I2C-0 I added dtparam=i2c_vc=on to the config.txt file. I am also using GPIO 11 (BCM pin 7) as a digital out. This works just fine with the Raspberry Pi Zero W. However, when I changed to a Pi 3 B+ (and bumped up the OS to the next release, but not sure that is the issue), the following occurs:

When I include dtparam=i2c_vc=on to the config.txt file I get access to the I2C-O bus, as expected. However, in addition to /dev/i2c-0 appearing, I also get /dev/i2c-10 and /dev/i2c-11, and when attempting to provision GPIO-11 in Pi4J, I no longer have access to GPIO-11 (BCM pin 7). My guess is that the mysterious appearance of I2C-11 and disappearance of GPIO-11 are related. As I was using GPIO-11 for something and I have already fabricated a PCB, this puts me into a bit of a bind.

I would much rather use the 3 B+ and not have to patch the physical hardware. This does not appear to be an issue with Pi4J. My guess/hope is that there is probably a trivial solution with device overlays, but no luck searching for this specific problem. Any help/pointers would be greatly appreciated.

Greenonline
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MountainPi
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1 Answers1

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The documentation states

        i2c_vc                  Set to "on" to enable the i2c interface
                                usually reserved for the VideoCore processor
                                (default "off")

The 2nd I²C interface is reserved for HATs (and also probably used for GPIO extension - although this is undocumented). It WAS usable on the older Pi, but effectively is unavailable. You can disable probing for HATs but AFAIK not the other services e.g. PWR LED etc).

The difference between the Pi3 and earlier models is easy to explain. The addition of wireless requires more GPIO so an extender was added and some of the on board circuitry e.g. LEDs was moved to the extender.

The Zero models lack the USB hub and Ethernet.

Milliways
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