Function solveBitTiming

app/src/IO/Drivers/GsUsbCanBackend.cpp:186–226

* @brief Solves gs_usb bit-timing segments for a target bitrate from BT_CONST limits. */

 * @brief Solves gs_usb bit-timing segments for a target bitrate from BT_CONST limits.
 */
[[nodiscard]] static bool solveBitTiming(const GsDeviceBtConst& bt,
                                         std::uint32_t bitrate,
                                         GsDeviceBitTiming& out)
{
  if (bitrate == 0 || bt.fclkCan == 0)
    return false;

  const std::uint32_t step = std::max<std::uint32_t>(1, bt.brpInc);
  for (std::uint32_t brp = bt.brpMin; brp <= bt.brpMax; brp += step) {
    const std::uint32_t divisor = bitrate * brp;
    if (divisor == 0 || (bt.fclkCan % divisor) != 0)
      continue;

    const std::uint32_t total = bt.fclkCan / divisor;
    if (total < 1 + bt.tseg1Min + bt.tseg2Min || total > 1 + bt.tseg1Max + bt.tseg2Max)
      continue;

    std::uint32_t tseg2 = static_cast<std::uint32_t>(std::lround(total * 0.125));
    tseg2               = std::clamp(tseg2, std::max<std::uint32_t>(1, bt.tseg2Min), bt.tseg2Max);
    if (total <= 1 + tseg2)
      continue;

    const std::uint32_t tseg1 = total - 1 - tseg2;
    if (tseg1 < bt.tseg1Min || tseg1 > bt.tseg1Max)
      continue;

    out.phaseSeg2 = tseg2;
    out.phaseSeg1 = std::max<std::uint32_t>(1, tseg1 / 2);
    out.propSeg   = tseg1 - out.phaseSeg1;
    if (out.propSeg == 0) {
      out.propSeg   = 1;
      out.phaseSeg1 = tseg1 - 1;
    }

    out.sjw = std::min(bt.sjwMax, tseg2);
    out.brp = brp;
    return true;
  }

  return false;
}

/**
 * @brief Decodes a received gs_host_frame; returns false for TX echoes that must be dropped.