tmc2209-uart 0.1.0

A no_std Rust driver for the TMC2209 stepper motor driver via UART
Documentation 
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//! CRC-8 calculation for TMC2209 UART communication.
//!
//! The TMC2209 uses CRC-8 with polynomial 0x07 (reflected).
//! This implementation uses the same lookup table as the official TMC-API.

/// CRC-8 lookup table for polynomial 0x07 (reflected).
///
/// This table is taken directly from the official Trinamic TMC-API.
#[rustfmt::skip]
const CRC_TABLE: [u8; 256] = [
    0x00, 0x91, 0xE3, 0x72, 0x07, 0x96, 0xE4, 0x75, 0x0E, 0x9F, 0xED, 0x7C, 0x09, 0x98, 0xEA, 0x7B,
    0x1C, 0x8D, 0xFF, 0x6E, 0x1B, 0x8A, 0xF8, 0x69, 0x12, 0x83, 0xF1, 0x60, 0x15, 0x84, 0xF6, 0x67,
    0x38, 0xA9, 0xDB, 0x4A, 0x3F, 0xAE, 0xDC, 0x4D, 0x36, 0xA7, 0xD5, 0x44, 0x31, 0xA0, 0xD2, 0x43,
    0x24, 0xB5, 0xC7, 0x56, 0x23, 0xB2, 0xC0, 0x51, 0x2A, 0xBB, 0xC9, 0x58, 0x2D, 0xBC, 0xCE, 0x5F,
    0x70, 0xE1, 0x93, 0x02, 0x77, 0xE6, 0x94, 0x05, 0x7E, 0xEF, 0x9D, 0x0C, 0x79, 0xE8, 0x9A, 0x0B,
    0x6C, 0xFD, 0x8F, 0x1E, 0x6B, 0xFA, 0x88, 0x19, 0x62, 0xF3, 0x81, 0x10, 0x65, 0xF4, 0x86, 0x17,
    0x48, 0xD9, 0xAB, 0x3A, 0x4F, 0xDE, 0xAC, 0x3D, 0x46, 0xD7, 0xA5, 0x34, 0x41, 0xD0, 0xA2, 0x33,
    0x54, 0xC5, 0xB7, 0x26, 0x53, 0xC2, 0xB0, 0x21, 0x5A, 0xCB, 0xB9, 0x28, 0x5D, 0xCC, 0xBE, 0x2F,
    0xE0, 0x71, 0x03, 0x92, 0xE7, 0x76, 0x04, 0x95, 0xEE, 0x7F, 0x0D, 0x9C, 0xE9, 0x78, 0x0A, 0x9B,
    0xFC, 0x6D, 0x1F, 0x8E, 0xFB, 0x6A, 0x18, 0x89, 0xF2, 0x63, 0x11, 0x80, 0xF5, 0x64, 0x16, 0x87,
    0xD8, 0x49, 0x3B, 0xAA, 0xDF, 0x4E, 0x3C, 0xAD, 0xD6, 0x47, 0x35, 0xA4, 0xD1, 0x40, 0x32, 0xA3,
    0xC4, 0x55, 0x27, 0xB6, 0xC3, 0x52, 0x20, 0xB1, 0xCA, 0x5B, 0x29, 0xB8, 0xCD, 0x5C, 0x2E, 0xBF,
    0x90, 0x01, 0x73, 0xE2, 0x97, 0x06, 0x74, 0xE5, 0x9E, 0x0F, 0x7D, 0xEC, 0x99, 0x08, 0x7A, 0xEB,
    0x8C, 0x1D, 0x6F, 0xFE, 0x8B, 0x1A, 0x68, 0xF9, 0x82, 0x13, 0x61, 0xF0, 0x85, 0x14, 0x66, 0xF7,
    0xA8, 0x39, 0x4B, 0xDA, 0xAF, 0x3E, 0x4C, 0xDD, 0xA6, 0x37, 0x45, 0xD4, 0xA1, 0x30, 0x42, 0xD3,
    0xB4, 0x25, 0x57, 0xC6, 0xB3, 0x22, 0x50, 0xC1, 0xBA, 0x2B, 0x59, 0xC8, 0xBD, 0x2C, 0x5E, 0xCF,
];

/// Calculate the CRC-8 checksum for a slice of bytes.
///
/// This uses the TMC2209's CRC polynomial (0x07) with bit reflection.
/// The result is bit-reversed as required by the TMC2209 protocol.
///
/// # Arguments
///
/// * `data` - The data bytes to calculate the CRC for (excluding the CRC byte itself)
///
/// # Returns
///
/// The CRC-8 checksum byte
pub fn compute(data: &[u8]) -> u8 {
    let mut crc = 0u8;

    for &byte in data {
        crc = CRC_TABLE[(crc ^ byte) as usize];
    }

    // Bit-reverse the result (as done in the TMC-API)
    // swap odd and even bits
    crc = ((crc >> 1) & 0x55) | ((crc & 0x55) << 1);
    // swap consecutive pairs
    crc = ((crc >> 2) & 0x33) | ((crc & 0x33) << 2);
    // swap nibbles
    crc = ((crc >> 4) & 0x0F) | ((crc & 0x0F) << 4);

    crc
}

/// Verify that the CRC of a complete message (including CRC byte) is valid.
///
/// # Arguments
///
/// * `data` - The complete message including the CRC byte as the last byte
///
/// # Returns
///
/// `true` if the CRC is valid, `false` otherwise
pub fn verify(data: &[u8]) -> bool {
    if data.is_empty() {
        return false;
    }
    let (payload, crc_byte) = data.split_at(data.len() - 1);
    compute(payload) == crc_byte[0]
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_crc_read_request() {
        // Example read request for GCONF (0x00) to slave 0
        let data = [0x05, 0x00, 0x00];
        let crc = compute(&data);
        // This should produce a valid CRC
        assert!(verify(&[0x05, 0x00, 0x00, crc]));
    }

    #[test]
    fn test_crc_write_request() {
        // Example write request
        let data = [0x05, 0x00, 0x80, 0x00, 0x00, 0x00, 0x40];
        let crc = compute(&data);
        assert!(verify(&[0x05, 0x00, 0x80, 0x00, 0x00, 0x00, 0x40, crc]));
    }
}