用 C# 讀取 GPS 資料的基類（適用於 Windows CE 作業系統）

GPS 基類架構

針對 Windows CE 平台，透過 P/Invoke 呼叫 coredll.dll 實現序列埠通訊與 NMEA 協議解析。

核心結構體與 API 宣告

• DCB：裝置控制區塊，設定波特率、奇偶校驗、資料位、停止位等
• COMMTIMEOUTS：通訊逾時設定
• OVERLAPPED：非同步 I/O 重疊結構
• API：CreateFile、GetCommState、BuildCommDCB、SetCommState、GetCommTimeouts、SetCommTimeouts、ReadFile、WriteFile、CloseHandle、GetLastError

主要方法

Open() 開啟序列埠

public void Open() {
    DCB dcb = new DCB(); COMMTIMEOUTS cto = new COMMTIMEOUTS();
    hComm = CreateFile(PortNum, GENERIC_READ | GENERIC_WRITE, 0, 0, OPEN_EXISTING, 0, 0);
    if (hComm == INVALID_HANDLE_VALUE) throw new ApplicationException("無法開啟序列埠！");
    GetCommTimeouts(hComm, ref cto);
    cto.ReadTotalTimeoutConstant = ReadTimeout;
    SetCommTimeouts(hComm, ref cto);
    GetCommState(hComm, ref dcb);
    dcb.BaudRate = BaudRate; dcb.ByteSize = ByteSize; dcb.Parity = Parity; dcb.StopBits = StopBits;
    dcb.flags = 1; if (Parity > 0) dcb.flags |= 2; // fBinary=1, fParity=1
    if (!SetCommState(hComm, ref dcb)) throw new ApplicationException("無法設定序列埠！");
    Opened = true;
}

Read/Write 讀寫資料

public byte[] Read(int NumBytes) {
    byte[] buf = new byte[NumBytes];
    if (hComm != INVALID_HANDLE_VALUE) {
        OVERLAPPED ovl = new OVERLAPPED(); int bytesRead = 0;
        ReadFile(hComm, buf, NumBytes, ref bytesRead, ref ovl);
        byte[] outBytes = new byte[bytesRead]; Array.Copy(buf, 0, outBytes, 0, bytesRead);
        return outBytes;
    } throw new ApplicationException("序列埠未開啟！");
}
public void Write(byte[] WriteBytes) {
    if (hComm != INVALID_HANDLE_VALUE) {
        OVERLAPPED ovl = new OVERLAPPED(); int bytesWritten = 0;
        WriteFile(hComm, WriteBytes, WriteBytes.Length, ref bytesWritten, ref ovl);
    } else throw new ApplicationException("序列埠未開啟！");
}

NMEA 協議解析

GetGPS() 從 $GPRMC 句式提取經度（X）、緯度（Y）、時間（T）、速度（V）：

• DM2DD()：度分格式轉十進制度格式
• T2Time()：日期時間字串轉 DateTime 並加 8 小時（UTC+8）

ScanPort() 掃描埠口

開啟埠口讀取 512 位元組，檢查是否含 $GP 標頭判斷 GPS 裝置是否就緒。

表單調用範例

透過 Timer 週期性讀取：

GPS ss_port = new GPS();
private void opengps(string ComPort) {
    ss_port.PortNum = ComPort; ss_port.BaudRate = 4800; ss_port.ByteSize = 8; ss_port.Parity = 0; ss_port.StopBits = 1; ss_port.ReadTimeout = 1000;
    if (ss_port.Opened) { ss_port.Close(); ss_port.Open(); } else ss_port.Open();
    timer1.Enabled = true;
}
private void timer1_Tick(object sender, EventArgs e) {
    if (ss_port.Opened) gpsread(); else ss_port.Open();
}
private void gpsread() {
    byte[] data = ss_port.Read(512);
    string gps = Encoding.ASCII.GetString(data, 0, data.Length);
    GetParam.GpsLongitude = ss_port.GetGPS(gps, "X");
    GetParam.GpsLatitude = ss_port.GetGPS(gps, "Y");
    GetParam.GpsSpeed = ss_port.GetGPS(gps, "V");
    GetParam.GpsTime = ss_port.GetGPS(gps, "T");
    // 狀態判斷與預設值處理...
}

輔助類 HexCon

十六進制字串與位元組陣列互轉。