Sound way of determining default i2c bus

[sgparry]

Hi,
As I understand it, most Pis use bus 1 for i2c by default, but some models use 0. What is the best way, using diozero, to determine which?
Thanks

[sgparry]

Not sure what planet I was on when I wrote this question - I meant i2c not DMA...

[EAGrahamJr]

Have you looked at https://www.diozero.com/utilityapps.html? The code for com.diozero.sampleapps.I2CDetect might get you somewhere -- at the minimum, you'd be able to scan a given controller to see if it finds any devices. 😃

[sgparry]

@EAGrahamJr thanks for the reply...
I need something lightweight; I am converting some Python library code that sets the default i2c bus for its constructors based on a version field (it is not clear as to which from the code). 99 times out of 100, it will be bus 1. Having googled around a bit, I think the following is sufficient in diozero:

    private static int getDefaultI2cBus() {
        BoardInfo boardInfo = DeviceFactoryHelper.getNativeDeviceFactory().getBoardInfo();
        String longName = boardInfo.getLongName();
        if (longName.equals("Raspberry Pi Model B v1.0") || longName.equals("Raspberry Pi Model B v1.1")) {
            return 0;
        } else {
            return 1;
        }
    }

The version strings correspond to legacy revisions 0002 and 0003. Can anyone confirm that this looks right or suggest better please?

[EAGrahamJr]

Well, there is the notion of not bothering to support such old boards 😃

If you're going that route, I wouldn't use hard-coded strings, but rather use the board's pcbRevision and select on the constants PCB_REV_1_0 and PCB_REV_1_1 - that way your code shouldn't break if Matt decides to tweak the board info.

You could also construct an I2CDevice with the target device address and just see if it's there with a probe": "if it's not on bus 1, try bus 0".

[sgparry]

Hey, I'm not using them, but I think that 2 of the original Model A s I have may be V1.1!
I went for getLongName to avoid having to compare three pieces of information (who knows what values a clone might return) but I think I will split the comparison up.
If I were writing my code from scratch I would probably probe, but I want to keep behaviour as close to the original python code as possible. Thanks!

[sgparry]

Slight problem, all the constants and the getPcbRevision are only accessible on the internal API version of the interface.

[EAGrahamJr]

🤔

[mattjlewis]

You should be able to cast the BoardInfo returned from the device factory getBoardInfo method to PiBoardInfo and then call the public operation getPcbRevision. The PCB_REV_ constants are all public in RaspberryPiBoardInfoProvider