bootloader_utils.hpp

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#pragma once
#include <array>
#include <cstddef>
#include <cstdint>
 
namespace tmc9660 {
 
static constexpr uint8_t reverseByte(uint8_t b) noexcept {
  b = (b & 0xF0) >> 4 | (b & 0x0F) << 4;
  b = (b & 0xCC) >> 2 | (b & 0x33) << 2;
  b = (b & 0xAA) >> 1 | (b & 0x55) << 1;
  return b;
}
 
static constexpr uint8_t crc8Bootloader(const uint8_t* data, size_t len) noexcept {
  uint16_t crc = 0;            // 9-bit register for polynomial division
  const uint16_t POLY = 0x107; // x^8 + x^2 + x^1 + x^0 in 9-bit form
 
  // Process each byte (bit-reversed, LSB-first)
  for (size_t i = 0; i < len; i++) {
    uint8_t byte_reversed = reverseByte(data[i]);
 
    // Feed 8 bits into CRC register (MSB-first from reversed byte)
    for (int bit = 7; bit >= 0; bit--) {
      crc = (crc << 1) | ((byte_reversed >> bit) & 1);
      if (crc & 0x100) { // If bit 8 is set
        crc ^= POLY;
      }
    }
  }
 
  // Append 8 zero bits (flush remaining data through CRC)
  for (int i = 0; i < 8; i++) {
    crc <<= 1;
    if (crc & 0x100) {
      crc ^= POLY;
    }
  }
 
  return static_cast<uint8_t>(crc & 0xFF);
}
 
} // namespace tmc9660