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问题：在异步访问我的 I2C 设备（在主循环而不是阻塞循环中轮询它）后，一旦我写入 USB 串行端口，就会出现 CPU 异常

背景：我有一个在 Microchip Studio 下运行的 Arduino 项目（用于通过 J-Link 接口进行调试）。我正在通过 I2C 与 VCNL4010 接近传感器通信。我有一个有效的同步函数，可以读取接近度：

Zult<uint16_t> ProximitySensor::readProximity(void) {
    auto res = setIntMask(0x80);
    if (res.isError())
        return Zult<uint16_t>(res);

    res = write8(VCNL4010_COMMAND, VCNL4010_MEASUREPROXIMITY);
    if (res.isError())
        return Zult<uint16_t>(res);
    auto start = millis();
    do {
        auto cmd = read8(VCNL4010_COMMAND);
        if (cmd.isError())
            return Zult<uint16_t>(cmd);
        if (cmd.getResult() & VCNL4010_PROXIMITYREADY) {
            return read16(VCNL4010_PROXIMITYDATA);
        }
        delay(1);
    } while (millis() - start < 1000);
    return Zult<uint16_t>(0, "timeout in readProximity");
}

此代码工作正常，但会阻塞我的主循环，直到传感器读取完成。我需要避免阻塞，因为我也在控制电机。我写了一个异步版本，分为以下功能：

Zult<bool> ProximitySensor::readProximityBegin() {
    auto res = setIntMask(0x80);
    if (res.isError())
        return Zult<uint16_t>(res);
    res = write8(VCNL4010_COMMAND, VCNL4010_MEASUREPROXIMITY);
    if (res.isError())
        return Zult<uint16_t>(res);
    asyncStart = millis();
    asyncReady = false;
    asyncResult = NotReadyZult;
}
    
bool ProximitySensor::readProximityReady() {
    return asyncReady;
}

void ProximitySensor::stopAsync() {
    asyncReady = true;
    asyncStart = 0;
}

void ProximitySensor::update() {
    if (asyncStart != 0) {
        auto cmd = read8(VCNL4010_COMMAND);
        if (cmd.isError()) {
            asyncResult = Zult<uint16_t>(cmd);
            stopAsync();
            return;
        }
        if (cmd.getResult() & VCNL4010_PROXIMITYREADY) {
            asyncResult = read16(VCNL4010_PROXIMITYDATA);
            stopAsync();
            return;
        }
        if (millis() - asyncStart > 1000) {
            asyncResult = Zult<uint16_t>(0, "timeout in readProximity");
            stopAsync();
        }
    }
}
    
Zult<uint16_t> ProximitySensor::readProximityResult() {
    return asyncResult;
}

作为对串行命令的响应，我readProximityBegin在主循环中调用并调用 update 直到readProximityReady变为真，此时我使用readProximityResult. 如前所述，一旦我在这一切之后写入 USB 串行端口，就会出现 CPU 异常（错误源于writeRTL 中的串行）。我不确定究竟是哪个异常，因为在 cortex_handlers.c 中，SAMD21 的 arduino 代码将各种异常路由到同一函数：

void Dummy_Handler(void)
{
#if defined DEBUG
  __BKPT(3); // this is where my debugger stops
#endif
  for (;;) { }
}

这是上面引用的我的 I2C 函数之一的示例：

Zult<uint8_t> ProximitySensor::read8(uint8_t command) {
    Wire.beginTransmission(_i2caddr);
    Wire.write(command);
    auto result = Wire.endTransmission();
    if (result != 0) {
        return Zult<uint8_t>((int)result, "Writing request to read8");
    }

    delayMicroseconds(170); // delay required

    Wire.requestFrom(_i2caddr, (uint8_t)1);
    auto start = millis();
    while (!Wire.available()) {
        if (millis() - start > 1000)
            return Zult<uint16_t>(0, "Timeout waiting for read");
    }
    return Zult<uint8_t>(Wire.read());
}
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