Chrome.serial.onReceive 事件划分字节以响应设备

Question

我正在为 Google Chrome 构建一个应用程序，它通过 COM (usb) 端口从设备获取一些字节。

代码：

// connects the device
function connect(port_name, timeout) {
    chrome.serial.connect(port_name, {
        bitrate: 115200,
        bufferSize: 32768,
        dataBits: "eight",
        stopBits: "one",
        parityBit: "no",
        sendTimeout: timeout,
        receiveTimeout: timeout
    }, function(connectionInfo) {
        if (typeof (connectionInfo) !== 'undefined') {
            if (typeof (connectionInfo.connectionId) !== 'undefined' && connectionInfo.connectionId < 1) {
                console.log('Connection error #1');
            } else {
                sessionStorage.setItem('connection', connectionInfo.connectionId);
            }
        }
    })
}
// sends bytes to device
function send_bytes(bytes) {
    var bytes_to_send = new Uint8Array(bytes);
    var connection = Number(sessionStorage.getItem('connection'));
    chrome.serial.send(connection, (bytes_to_send).buffer, function(sent_data) {});
}
// recieves the data
chrome.serial.onReceive.addListener(function(data_recieved) {
    var arr = new Uint8Array(data_recieved.data);
    var final_hex = [];
    for (byte in arr) {
        final_hex.push(arr[byte].toString(16));
    }
    console.log('====== HEX ======');
    console.log(final_hex);
});

如果我运行控制台中的下一个代码几次：

connect('COM5',15000); // we connected!
send_bytes([0x05, 0xAD, 0x1E, 0x00, 0x00, 0x00, 0xB6]); // bytes away! ( runs N times)

通常我会收到正确的 HEX 序列：

["6", "2", "16", "ad", "0", "0", "0", "0", "0", "0", "10", "a", "6", "10", "20", "58", "2", "0", "0", "b5", "c0", "ea", "6a", "0", "c", "34"]

但有时我会在两个 .onReceive 回调中分别接收字节：

 ["6", "2", "16", "ad", "0", "0", "0", "0", "0", "0", "10", "a", "6", "10", "20"]
 ["58", "2", "0", "0", "b5", "c0", "ea", "6a", "0", "c", "34"]

乍一看，发生这种情况是因为Chrome认为设备已完成发送数据，并且下一部分数据来自设备的新应答。我在 API 文档中没有找到 "time to wait for the next byte while receiving responce from device" 的任何选项。

如何防止字节序列被chrome.serial.onReceive分隔？

Answer 1

如果传入数组小于最小响应长度，则推迟处理，保存块并在下一个事件中处理。

var MIN_RESPONSE_LENGTH = 26;
var incoming = new Uint8Array();

chrome.serial.onReceive.addListener(function(info) {
    appendBuffer(info.data);
    if (incoming.length < MIN_RESPONSE_LENGTH) {
        setTimeout(function() {
            console.log('Timeout waiting for the data, got only:', incoming);
        }, 1000);
        return;
    }
    // process
    console.log(incoming);
    ................
    // reset
    incoming = new Uint8Array();
});

function appendBuffer(arraybuffer) {
    var tmp = new Uint8Array(incoming.length + arraybuffer.byteLength);
    tmp.set(incoming, 0);
    tmp.set(new Uint8Array(arraybuffer), incoming.length);
    incoming = tmp;
}

Chrome.serial.onReceive 事件划分字节以响应设备

Chrome.serial.onReceive event divides bytes in responce from device

javascript

google-chrome

serial-port

google-chrome-app