i2cdev2 0.4.0

Provides API for safe access to Linux i2c device interface. https://www.kernel.org/doc/Documentation/i2c/dev-interface
Documentation 
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// Copyright 2018, Piers Finlayson <piers@piersandkatie.com>
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/license/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option.  This file may not be copied, modified, or distributed
// except according to those terms.extern crate i2cdev;

extern crate i2cdev;
extern crate docopt;

#[cfg(any(target_os = "linux", target_os = "android"))]
use i2cdev::linux::{LinuxI2CBus, I2CMsg};
#[cfg(any(target_os = "linux", target_os = "android"))]
use i2cdev::core::I2CBus;

use std::env::args;
use docopt::Docopt;

const USAGE: &str = "
Reads registers from a PCA9956B IC via Linux i2cdev.

Assumes the PCA9956B is using address 0x20.

Usage:
  pca9956b <device>
  pca9956b (-h | --help)
  pca9956b --version

Options:
  -h --help    Show this help text.
  --version    Show version.
";

const ADDR: u16 = 0x20;

#[cfg(any(target_os = "linux", target_os = "android"))]
fn main() {
    let args = Docopt::new(USAGE)
        .and_then(|d| d.argv(args()).parse())
        .unwrap_or_else(|e| e.exit());
    let path = args.get_str("<device>");
    let mut bus = match LinuxI2CBus::new(path) {
        Ok(bus) => bus,
        Err(_e) => {
            println!("Error opening I2C Bus {} {}", path, _e);
            return
        }
    };
    println!("Opened I2C Bus OK: {}", path);

    // Build two I2C messages:
    // 1) Write the MODE1 register address, with top bit indcating auto-
    //    increment should be enabled
    // 2) Read 10 bytes from the current register onwards
    let mut dataw: Vec<u8> = vec![0b1000_0000]; 
    let mut data: Vec<u8> = vec![0; 10]; 
    let mut msgs: Vec<I2CMsg> = Vec::new();
    msgs.push(I2CMsg::new(ADDR, &mut dataw));
    msgs.push(I2CMsg::new(ADDR, &mut data));
    msgs[1].set_read();

    // Send the messages to the kernel to process
    match bus.rdwr(&mut msgs) {
        Ok(rc) => {
            println!("Successful RDWR call: {} messages processed", rc)
        },
        Err(_e) => {
            println!("Error reading/writing {}", _e);
            return
        },
    }

    // Print the data read from the device.  A recently reset PCA9956B should
    // return:
    // 0x8005000000000000ff00
    let mut output = "Result: 0x".to_string();
    let data = msgs[1].data();
    for byte in data {
        output = format!("{}{:02x}", output, byte);
    }
    println!("{}", output);
}