Arduino Uno + BME280 compilation error

[rkudryashov]

I decided to move my question from #301 to a separate discussion

I am trying to use a bme280 environmental sensor connected to an Arduino Uno using I2C. I do it like this:

fn measure_bme() {
    let dp = Peripherals::take().unwrap();
    let pins = arduino_hal::pins!(dp);

    let mut i2c = arduino_hal::i2c::I2c::new(
        dp.TWI,
        pins.a4.into_pull_up_input(),
        pins.a5.into_pull_up_input(),
        50000,
    );

    let mut bme280= BME280::new_primary(i2c);
}

The compilation error looks like this:

error[E0277]: the trait bound `avr_hal_generic::i2c::I2c<Atmega, arduino_hal::pac::TWI, avr_hal_generic::port::Pin<Input, PC4>, avr_hal_generic::port::Pin<Input, PC5>, MHz16>: embedded_hal::i2c::blocking::I2c` is not satisfied
  --> src\main.rs:30:41
   |
30 |     let mut bme280= BME280::new_primary(i2c);
   |                     ------------------- ^^^ the trait `embedded_hal::i2c::blocking::I2c` is not implemented for `avr_hal_generic::i2c::I2c<Atmega, arduino_hal::pac::TWI, avr_hal_generic::port::Pin<Input, PC4>, avr_hal_generic::port::Pin<Input, PC5>, MHz16>`
   |                     |
   |                     required by a bound introduced by this call
   |
   = help: the trait `embedded_hal::i2c::blocking::I2c<A>` is implemented for `&mut T`
note: required by a bound in `bme280::i2c::BME280::<I2C>::new_primary`
  --> C:\Users\User\.cargo\registry\src\github.com-1ecc6299db9ec823\bme280-0.4.4\src\i2c.rs:22:10
   |
22 |     I2C: I2c + ErrorType,
   |          ^^^ required by this bound in `bme280::i2c::BME280::<I2C>::new_primary`

For more information about this error, try `rustc --explain E0277`.
warning: `embedded` (bin "embedded") generated 2 warnings
error: could not compile `embedded` due to previous error; 2 warnings emitted

Dependencies are:

arduino-hal = { git = "https://github.com/rahix/avr-hal", rev = "81edfcd908be8d3b2cd763cf2dc76aedbb22286b", features = ["arduino-uno"] }
embedded-hal = "0.2.7"
panic-halt = "0.2.0"
bme280 = "0.4.4"

I tried to implement it as it was in https://github.com/maspetsberger/rust-esp32-bme280/blob/master/src/main.rs#L30.

The library (https://github.com/VersBinarii/bme280-rs) also contains an example of using I2C.

Could you help me fix the compilation error? Is it worth to try using SPI?

[Rahix]

Hi, the problem is that the library in question uses embedded-hal version 1.0.0-alpha.7 (https://github.com/VersBinarii/bme280-rs/blob/efd5a52273014d98d41b85e454142c5c75ef6139/Cargo.toml#L16) while we're still using 0.2.7. These two are incompatible so there isn't an easy way to get them to work together...

What you can try doing is building a compatibility wrapper around our type which then implements the trait from 1.0.0-alpha.7. Something like this:

Cargo.toml

[dependencies.eh-alpha]
package = "embedded-hal"
version = "1.0.0-alpha.7"

main.rs

use eh_alpha::i2c::blocking::I2c as I2cAlpha;

struct WrappedI2c<T>(T);

impl<T> I2cAlpha for WrappedI2c<T>
where
  T: embedded_hal:: /* old I2c traits */
{
  ...
}

[rkudryashov]

Thanks, that helped me to fix the code. Now I try to get measurements; it requires to pass a delay. I define the delay as follows:

struct CustomDelay;

impl DelayUsAlpha for CustomDelay {
    type Error = CustomError;

    fn delay_us(&mut self, us: u32) -> Result<(), Self::Error> {
        delay_us(us);
        Ok(())
    }
}

(I didn't manage to pass Delay instance from arduino_hal::delay)

The code for measurements is:

    ufmt::uwriteln!(serial, "creating I2C bus...").unwrap();
    let mut i2c = arduino_hal::hal::i2c::I2c::new(
        dp.TWI,
        pins.a4.into_pull_up_input(),
        pins.a5.into_pull_up_input(),
        50000,
    );

    // there are multiple delay providers, this seems to be most frequently used
    let mut delay = CustomDelay;

    // create the BME280 using the primary I2C address 0x76
    ufmt::uwriteln!(serial, "creating BME280...").unwrap();
    let mut bme280= BME280::new_primary(WrappedI2c(i2c));

    // initialize the sensor
    ufmt::uwriteln!(serial, "initializing BME280...").unwrap();
    bme280.init(&mut delay).unwrap();

    // measure temperature, pressure, and humidity
    ufmt::uwriteln!(serial, "starting measurements...").unwrap();
    for _ in 0..100 {
        let measurements = bme280.measure(&mut delay).unwrap();

It prints the following:

creating I2C bus...
creating BME280...
initializing BME280...

That is the program hangs at BME280 initialization (bme280.init). Maybe specified delay implementation is incrorrect? Or what else could be wrong?

[rkudryashov]

This is most likely because I forgot to implement methods of I2cAlpha trait

[rkudryashov]

I implemented methods that exist both in 0.2.7 and alpha versions:

struct WrappedI2c(arduino_hal::hal::i2c::I2c<MHz12>);

impl I2cAlpha for WrappedI2c
{
    fn read(&mut self, address: SevenBitAddress, buffer: &mut [u8]) -> Result<(), Self::Error> {
        Ok(self.0.read(address, buffer)?)

    }

    fn write(&mut self, address: SevenBitAddress, bytes: &[u8]) -> Result<(), Self::Error> {
        Ok(self.0.write(address, bytes)?)
    }

    fn write_iter<B>(&mut self, address: SevenBitAddress, bytes: B) -> Result<(), Self::Error> where B: IntoIterator<Item=u8> {
        todo!()
    }

    fn write_read(&mut self, address: SevenBitAddress, bytes: &[u8], buffer: &mut [u8]) -> Result<(), Self::Error> {
        Ok(self.0.write_read(address, bytes, buffer)?)
    }

    fn write_iter_read<B>(&mut self, address: SevenBitAddress, bytes: B, buffer: &mut [u8]) -> Result<(), Self::Error> where B: IntoIterator<Item=u8> {
        todo!()
    }

    fn transaction<'a>(&mut self, address: SevenBitAddress, operations: &mut [Operation<'a>]) -> Result<(), Self::Error> {
        todo!()
    }

    fn transaction_iter<'a, O>(&mut self, address: SevenBitAddress, operations: O) -> Result<(), Self::Error> where O: IntoIterator<Item=Operation<'a>> {
        todo!()
    }
}

Now the result is the same: the program hangs. What else I can do? Which of todo methods needs to be implemented? Is there a chance that embedded-hal transitive dependency will be updated to alpha version?

[Rahix]

Hm, maybe add a panic handler like this one: https://github.com/Rahix/avr-hal/blob/main/examples/arduino-uno/src/bin/uno-panic.rs

It prints out the line where it panicked so you can then guess which method is missing.

[rkudryashov]

Thanks, I'll try it later