Support for GPIO over I2C (PCF8574) on Pi5

[mpilone]

I need to support GPIO over I2C using the PCF8574 chip. It looks like this might have been provided by the pigpio provider pre Pi5 but that is no longer supported. I see on the linuxfs provider that "linuxfs-digital-input" is under construction. Is that where this would be supported?

I found an old reference to a PCF8574GpioProvider but I think that's based on the old Pi4J v1 and not available in Pi4J v2.

So, is there any support for in v2 for I2C GPIO? If not, what's the best approach for adding it? Implementing a new GPIO provider that takes the I2C bus as a parameter? I assume there's no support in gpiod as an i2c device isn't directly exposed as a GPIO character device but maybe I'm wrong?

Any guidance here would be appreciated. Thanks,
-mike

[taartspi]

Evening.
Yes there is a GPIOD provider for digital input and output pins.

As far as the pcf 8574. I have a simple usage in a V2 example to drive a display via linuxfs-i2c.
https://github.com/Pi4J/pi4j-example-devices/tree/master/src/main/java/com/pi4j/devices/pcf8574a_lcd1602a

Does this answer your question ?

[mpilone]

Thanks for the code sample. I guess my question is if there's any existing code that exposes the PCF8574 as a DigitalInput/DigitalOutput in Pi4J. That is, a provider that would allow me to create an input like:

var config = DigitalInput.newConfigBuilder(pi4j)
        .load(properties)
        .build();

var input = pi4j.din().create(config);

input.addListener(e -> {
    if (e.state() == DigitalState.HIGH) {
        console.println("Button is pressed");
    }
});

while using the PCF8574 via I2C and its interrupt pin under the hood? I'm sure I could implement a custom GPIO provider and use the existing I2C support in the implementation, but I wanted to check if something already existed.

-mike

[taartspi]

Mike. Ok I understand your question. And no that specific an implementation does not exist. It was decided in V2 that no devices would be implemented rather user offered examples would be located in other repos and the Pi4j V2 was limited to gpio access at the basic provider level

[mpilone]

Got it. Thanks for the answer. I'll see what I can come up with but I didn't want to duplicate existing work if there was already a solution.

-mike