The Microchip mcp23x17 GPIO expander -- Now with more Rust

This is a Rust Embedded HAL crate to work with a GPIO expander. I bought this chip just to play with, so don't expect battle hardened code here. Ideally one day it will expose embedded-hal style GPIO pins but that's not a priority.

In fact, nothing here is a priority. Do you feel like making it better? Let me know!

lib.rs:

Rust Library for the Microchip MCP23X17

In its current incarnation, this only supports I2C but the register map is the same for SPI as well.

Internally, the chip supports a segreggated layout of registers to make two 8 bit GPIO ports or can interleave the registers to emulate one 16 bit GPIO port. This library works on the former layout and so disables setting BANK when calling set_config().

use linux_hal::I2cdev;
use mcp23x17::{
    Mcp23x17 as Expander,  
    Port
};

fn main() -> Result<(), Box<Error>> {
    let i2c = I2cdev::new("/dev/i2c-1")?;
    let mut exp = Expander::new(i2c)?;

    exp.select_port(Port::B);
    exp.set_direction(0x00)?;
    exp.set_data(0xff)?;
}

Implementation details taken from http://ww1.microchip.com/downloads/en/DeviceDoc/20001952C.pdf