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#![no_std]
extern crate byteorder;
extern crate embedded_hal;
use byteorder::{ByteOrder, BigEndian};
use embedded_hal::blocking::delay::DelayMs;
use embedded_hal::blocking::i2c::{Read, Write, WriteRead};
const CRC8_POLYNOMIAL: u8 = 0x31;
const I2C_ADDRESS: u8 = 0x70;
pub struct SHTC1<I2C, D> {
i2c: I2C,
delay: D,
}
impl<I2C, D, E> SHTC1<I2C, D>
where
I2C: Read<Error = E> + Write<Error = E> + WriteRead<Error = E>,
D: DelayMs<u8>,
{
pub fn new(i2c: I2C, delay: D) -> Self {
SHTC1 { i2c, delay }
}
fn command(&mut self, command: Command) -> Result<(), Error<E>> {
self.i2c
.write(I2C_ADDRESS, &command.value())
.map_err(Error::I2c)
}
pub fn measure(&mut self) -> Result<Measurement, Error<E>> {
let raw = self.measure_raw()?;
Ok(convert(&raw))
}
pub fn measure_raw(&mut self) -> Result<MeasurementRaw, Error<E>> {
self.command(Command::Measure(ClockStretch::Disabled, MeasurementOrder::TFirst))?;
self.delay.delay_ms(15);
let mut buf = [0; 6];
self.i2c.read(I2C_ADDRESS, &mut buf)
.map_err(Error::I2c)?;
self.validate_crc(&buf[0..3])?;
self.validate_crc(&buf[3..6])?;
let temperature = BigEndian::read_u16(&buf[0..2]);
let humidity = BigEndian::read_u16(&buf[3..5]);
Ok(MeasurementRaw{ temperature, humidity })
}
pub fn read_id(&mut self) -> Result<u16, Error<E>> {
self.command(Command::ReadID)?;
let mut id_bytes = [0; 3];
self.i2c
.read(I2C_ADDRESS, &mut id_bytes)
.map_err(Error::I2c)?;
self.validate_crc(&id_bytes[0..3])?;
Ok(BigEndian::read_u16(&id_bytes[0..2]))
}
pub fn release(self) -> I2C {
self.i2c
}
pub fn reset(&mut self) -> Result<(), Error<E>> {
self.command(Command::SoftReset)?;
Ok(())
}
fn validate_crc(&self, data: &[u8]) -> Result<(), Error<E>> {
match crc8(data) {
0x00 => Ok(()),
_ => Err(Error::Crc),
}
}
}
pub fn convert(m: &MeasurementRaw) -> Measurement {
Measurement{
temperature: convert_temperature(m.temperature),
humidity: convert_humidity(m.humidity),
}
}
fn convert_temperature(raw: u16) -> i32 {
-4500 + (17500 * raw as i32) / 65535
}
fn convert_humidity(raw: u16) -> i32 {
(10000 * raw as i32) / 65535
}
fn crc8(data: &[u8]) -> u8 {
let mut crc: u8 = 0xff;
for byte in data {
crc ^= byte;
for _ in 0..8 {
if (crc & 0x80) > 0 {
crc = (crc << 1) ^ CRC8_POLYNOMIAL;
} else {
crc <<= 1;
}
}
}
crc
}
#[derive(Debug)]
pub enum Error<E> {
Crc,
I2c(E),
}
enum Command {
Measure(ClockStretch, MeasurementOrder),
SoftReset,
ReadID,
}
#[allow(dead_code)]
enum ClockStretch {
Enabled,
Disabled,
}
#[derive(Copy, Clone)]
pub enum MeasurementOrder {
TFirst,
HFirst,
}
#[derive(Debug)]
pub struct Measurement {
pub temperature: i32,
pub humidity: i32,
}
#[derive(Debug)]
pub struct MeasurementRaw {
pub temperature: u16,
pub humidity: u16,
}
impl Command {
fn value(&self) -> [u8; 2] {
use ClockStretch::Enabled as CSEnabled;
use ClockStretch::Disabled as CSDisabled;
use MeasurementOrder::*;
match *self {
Command::Measure(CSEnabled, TFirst) => [0x7Cu8, 0xA2u8],
Command::Measure(CSEnabled, HFirst) => [0x5Cu8, 0x24u8],
Command::Measure(CSDisabled, TFirst) => [0x78u8, 0x66u8],
Command::Measure(CSDisabled, HFirst) => [0x58u8, 0xE0u8],
Command::SoftReset => [0x80, 0x5D],
Command::ReadID => [0xEF, 0xC8],
}
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn crc() {
assert_eq!(crc8(&[0x00u8]), 0xAC);
assert_eq!(crc8(&[0xBEu8, 0xEFu8]), 0x92);
}
}