urm37 1.1.2

Platform-agnostic no_std driver for the DFRobot URM37 V4.0 ultrasonic distance sensor (UART, PWM, Analog)
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150

//! # URM37 UART Example for Arduino Mega 2560
//!
//! Demonstrates UART communication for distance measurement.
//!
//! ## Hardware Setup
//! - **USART0** (D0/D1): Communication with computer (57600 baud)
//! - **USART1** (D18/D19): URM37 sensor (9600 baud)
//! - **Arduino Mega 2560**
//!
//! ## Output Format
//! ```text
//! [DISTANCE] X cm
//! [ERROR]
//! ```
//!
//! ## Build & Run
//! ```bash
//! cargo build --example mega2560_uart --features blocking
//! ```

#![no_std]
#![no_main]

use panic_halt as _;
use urm37::uart::Urm37Uart;
use ufmt::uwriteln;
use embedded_io::{Read, Write, ReadExactError, ErrorType};
use embedded_hal_0_2::serial as hal_serial;

/// UART adapter implementing embedded_io traits for arduino_hal USART
struct UsartAdapter<T> {
    serial: T,
}

#[derive(Debug, Copy, Clone)]
struct UsartError;

impl core::fmt::Display for UsartError {
    fn fmt(&self, _f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        Ok(())
    }
}

impl core::error::Error for UsartError {}

impl embedded_io::Error for UsartError {
    fn kind(&self) -> embedded_io::ErrorKind {
        embedded_io::ErrorKind::Other
    }
}

impl<T> ErrorType for UsartAdapter<T> {
    type Error = UsartError;
}

impl<T: hal_serial::Read<u8>> Read for UsartAdapter<T> {
    fn read(&mut self, buf: &mut [u8]) -> Result<usize, Self::Error> {
        if buf.is_empty() {
            return Ok(0);
        }

        const MAX_ATTEMPTS: u32 = 50000;
        let mut attempts = 0u32;

        loop {
            match self.serial.read() {
                Ok(byte) => {
                    buf[0] = byte;
                    return Ok(1);
                }
                Err(nb::Error::WouldBlock) => {
                    attempts += 1;
                    if attempts >= MAX_ATTEMPTS {
                        return Err(UsartError);
                    }
                }
                Err(_) => return Err(UsartError),
            }
        }
    }
}

impl<T: hal_serial::Write<u8>> Write for UsartAdapter<T> {
    fn write(&mut self, buf: &[u8]) -> Result<usize, Self::Error> {
        for &byte in buf {
            match nb::block!(self.serial.write(byte)) {
                Ok(()) => {}
                Err(_) => return Err(UsartError),
            }
        }
        Ok(buf.len())
    }

    fn flush(&mut self) -> Result<(), Self::Error> {
        Ok(())
    }
}

#[allow(dead_code)]
trait ReadExact: Read {
    fn read_exact(&mut self, buf: &mut [u8]) -> Result<(), embedded_io::ReadExactError<Self::Error>> {
        let mut n = 0;
        while n < buf.len() {
            match self.read(&mut buf[n..])? {
                0 => return Err(ReadExactError::UnexpectedEof),
                m => n += m,
            }
        }
        Ok(())
    }
}

impl<T: Read> ReadExact for T {}

#[arduino_hal::entry]
fn main() -> ! {
    let dp = arduino_hal::Peripherals::take().unwrap();
    let pins = arduino_hal::pins!(dp);

    // Serial for output to computer (USART0)
    let mut output = arduino_hal::Usart::new(
        dp.USART0,
        pins.d0,
        pins.d1.into_output(),
        arduino_hal::hal::usart::BaudrateArduinoExt::into_baudrate(57600),
    );

    // Serial for URM37 sensor (USART1)
    let sensor_serial = arduino_hal::Usart::new(
        dp.USART1,
        pins.d19,
        pins.d18.into_output(),
        arduino_hal::hal::usart::BaudrateArduinoExt::into_baudrate(9600),
    );

    let adapter = UsartAdapter { serial: sensor_serial };
    let mut sensor = Urm37Uart::new(adapter);

    loop {
        match sensor.read_distance() {
            Ok(distance) => {
                uwriteln!(&mut output, "[DISTANCE] {} cm", distance).ok();
            }
            Err(_) => {
                uwriteln!(&mut output, "[ERROR]").ok();
            }
        }
        arduino_hal::delay_ms(500);
    }
}