embedded-hal traits: synchronous bitbang i2c

Implementation of embedded-hal i2c traits using
blocking gpio bitbang approach.

Signed-off-by: Sergey Matyukevich <geomatsi@gmail.com>

src/i2c.rs

@@ -0,0 +1,334 @@
+/*!
+  # Synchronous implementation of embedded-hal I2C traits based on GPIO bitbang
+
+
+  This implementation consumes the following hardware resources:
+  periodic timer to mark clock cycles and
+  two gpio pins for SDA and SCL lines.
+
+  ## Hardware requirements
+
+  1. Configure gpio pins as Open-Drain outputs
+  2. Configure timer frequency to be twice as required i2c clock
+
+  ## Blue Pill example
+
+  Here is a sample code for LM75A I2C temperature sensor
+  on Blue Pill or any other stm32f1xx board:
+
+  ```rust
+   extern crate stm32f1xx_hal as hal;
+   use hal::prelude::*;
+   use hal::timer::Timer;
+
+   extern crate lm75;
+   use lm75::{Lm75, SlaveAddr};
+
+   use bitbang_hal;
+
+   ...
+
+   let dp = hal::stm32::Peripherals::take().unwrap();
+   let mut rcc = dp.RCC.constrain();
+   let mut gpioa = dp.GPIOA.split(&mut rcc.apb2);
+
+   let mut flash = dp.FLASH.constrain();
+   let clocks = rcc
+        .cfgr
+        .use_hse(8.mhz())
+        .sysclk(32.mhz())
+        .pclk1(16.mhz())
+        .freeze(&mut flash.acr);
+
+    let tmr = Timer::tim3(dp.TIM3, 200.khz(), clocks, &mut rcc.apb1);
+    let scl = gpioa.pa1.into_open_drain_output(&mut gpioa.crl);
+    let sda = gpioa.pa2.into_open_drain_output(&mut gpioa.crl);
+
+    let i2c = bitbang_hal::i2c::I2cBB::new(scl, sda, tmr);
+    let mut sensor = Lm75::new(i2c, SlaveAddr::default());
+    let temp = sensor.read_temperature().unwrap();
+
+    ...
+
+  ```
+
+*/
+
+use embedded_hal::blocking::i2c::{Read, Write, WriteRead};
+use embedded_hal::digital::v2::{InputPin, OutputPin};
+use embedded_hal::timer::{CountDown, Periodic};
+use nb::block;
+
+/// I2C error
+#[derive(Debug, Eq, PartialEq)]
+pub enum Error {
+    /// No ack received
+    NoAck,
+    /// Invalid input
+    InvalidData,
+    /// SDA pin error
+    SDAFailure,
+    /// SCL pin error
+    SCLFailure,
+    /// Timer error
+    CLKFailure,
+}
+
+/// I2C structure
+pub struct I2cBB<SCL, SDA, CLK>
+where
+    SCL: OutputPin,
+    SDA: OutputPin + InputPin,
+    CLK: CountDown + Periodic,
+{
+    scl: SCL,
+    sda: SDA,
+    clk: CLK,
+}
+
+impl<SCL, SDA, CLK> I2cBB<SCL, SDA, CLK>
+where
+    SCL: OutputPin,
+    SDA: OutputPin + InputPin,
+    CLK: CountDown + Periodic,
+{
+    pub fn new(scl: SCL, sda: SDA, clk: CLK) -> Self {
+        I2cBB { scl, sda, clk }
+    }
+
+    fn scl_set_low(&mut self) -> Result<(), Error> {
+        self.scl.set_low().map_err(|_| Error::SCLFailure)
+    }
+
+    fn sda_set_low(&mut self) -> Result<(), Error> {
+        self.sda.set_low().map_err(|_| Error::SDAFailure)
+    }
+
+    fn scl_set_high(&mut self) -> Result<(), Error> {
+        self.scl.set_high().map_err(|_| Error::SCLFailure)
+    }
+
+    fn sda_set_high(&mut self) -> Result<(), Error> {
+        self.sda.set_high().map_err(|_| Error::SDAFailure)
+    }
+
+    fn clk_wait(&mut self) -> Result<(), Error> {
+        block!(self.clk.wait()).map_err(|_| Error::CLKFailure)
+    }
+
+    fn i2c_start(&mut self) -> Result<(), Error> {
+        self.scl_set_high()?;
+        self.sda_set_high()?;
+        self.clk_wait()?;
+
+        self.sda_set_low()?;
+        self.clk_wait()?;
+
+        self.scl_set_low()?;
+        self.clk_wait()?;
+
+        Ok(())
+    }
+
+    fn i2c_stop(&mut self) -> Result<(), Error> {
+        self.scl_set_high()?;
+        self.clk_wait()?;
+
+        self.sda_set_high()?;
+        self.clk_wait()?;
+
+        Ok(())
+    }
+
+    fn i2c_is_ack(&mut self) -> Result<bool, Error> {
+        self.sda_set_high()?;
+        self.scl_set_high()?;
+        self.clk_wait()?;
+
+        let ack = self.sda.is_low().map_err(|_| Error::SDAFailure)?;
+
+        self.scl_set_low()?;
+        self.sda_set_low()?;
+        self.clk_wait()?;
+
+        Ok(ack)
+    }
+
+    fn i2c_read_byte(&mut self, ack: bool) -> Result<u8, Error> {
+        let mut byte: u8 = 0;
+
+        self.sda_set_high()?;
+
+        for i in 0..8 {
+            self.scl_set_high()?;
+            self.clk_wait()?;
+
+            if self.sda.is_high().map_err(|_| Error::SDAFailure)? {
+                byte |= 1 << (7 - i);
+            }
+
+            self.scl_set_low()?;
+            self.clk_wait()?;
+        }
+
+        if ack {
+            self.sda_set_low()?;
+        } else {
+            self.sda_set_high()?;
+        }
+
+        self.scl_set_high()?;
+        self.clk_wait()?;
+
+        self.scl_set_low()?;
+        self.sda_set_low()?;
+        self.clk_wait()?;
+
+        Ok(byte)
+    }
+
+    fn i2c_write_byte(&mut self, byte: u8) -> Result<(), Error> {
+        for bit in 0..8 {
+            let val = (byte >> (7 - bit)) & 0b1;
+
+            if val == 1 {
+                self.sda_set_high()?;
+            } else {
+                self.sda_set_low()?;
+            }
+
+            self.scl_set_high()?;
+            self.clk_wait()?;
+
+            self.scl_set_low()?;
+            self.sda_set_low()?;
+            self.clk_wait()?;
+        }
+
+        Ok(())
+    }
+}
+
+impl<SCL, SDA, CLK> Write for I2cBB<SCL, SDA, CLK>
+where
+    SCL: OutputPin,
+    SDA: OutputPin + InputPin,
+    CLK: CountDown + Periodic,
+{
+    type Error = Error;
+
+    fn write(&mut self, addr: u8, output: &[u8]) -> Result<(), Self::Error> {
+        if output.is_empty() {
+            return Ok(());
+        }
+
+        // ST
+        self.i2c_start()?;
+
+        // SAD + W
+        self.i2c_write_byte((addr << 1) | 0x0)?;
+        if !self.i2c_is_ack()? {
+            return Err(Error::NoAck);
+        }
+
+        // write output to slave
+        for byte in output {
+            self.i2c_write_byte(*byte)?;
+
+            if !self.i2c_is_ack()? {
+                return Err(Error::NoAck);
+            }
+        }
+
+        // SP
+        self.i2c_stop()?;
+
+        Ok(())
+    }
+}
+
+impl<SCL, SDA, CLK> Read for I2cBB<SCL, SDA, CLK>
+where
+    SCL: OutputPin,
+    SDA: OutputPin + InputPin,
+    CLK: CountDown + Periodic,
+{
+    type Error = Error;
+
+    fn read(&mut self, addr: u8, input: &mut [u8]) -> Result<(), Self::Error> {
+        if input.is_empty() {
+            return Ok(());
+        }
+
+        // ST
+        self.i2c_start()?;
+
+        // SAD + R
+        self.i2c_write_byte((addr << 1) | 0x1)?;
+        if !self.i2c_is_ack()? {
+            return Err(Error::NoAck);
+        }
+
+        // read bytes from slave
+        for i in 0..input.len() {
+            input[i] = self.i2c_read_byte(i != (input.len() - 1))?;
+        }
+
+        // SP
+        self.i2c_stop()?;
+
+        Ok(())
+    }
+}
+
+impl<SCL, SDA, CLK> WriteRead for I2cBB<SCL, SDA, CLK>
+where
+    SCL: OutputPin,
+    SDA: OutputPin + InputPin,
+    CLK: CountDown + Periodic,
+{
+    type Error = Error;
+
+    fn write_read(&mut self, addr: u8, output: &[u8], input: &mut [u8]) -> Result<(), Self::Error> {
+        if output.is_empty() || input.is_empty() {
+            return Err(Error::InvalidData);
+        }
+
+        // ST
+        self.i2c_start()?;
+
+        // SAD + W
+        self.i2c_write_byte((addr << 1) | 0x0)?;
+        if !self.i2c_is_ack()? {
+            return Err(Error::NoAck);
+        }
+
+        // write output to slave
+        for byte in output {
+            self.i2c_write_byte(*byte)?;
+
+            if !self.i2c_is_ack()? {
+                return Err(Error::NoAck);
+            }
+        }
+
+        // SR
+        self.i2c_start()?;
+
+        // SAD + R
+        self.i2c_write_byte((addr << 1) | 0x1)?;
+        if !self.i2c_is_ack()? {
+            return Err(Error::NoAck);
+        }
+
+        // read output from slave
+        for i in 0..input.len() {
+            input[i] = self.i2c_read_byte(i != (input.len() - 1))?;
+        }
+
+        // SP
+        self.i2c_stop()?;
+
+        Ok(())
+    }
+}