pyserial timeout=1 || timeout=0.01

昨天在做串口通信时候发现，串口参数（timeout=1 || timeout=0.01）对通信的读数据竟然影响很大，代码如下：

self.ser = serial.Serial(port=serialName,
                        timeout=0.01,
                        baudrate=115200,
                        parity=serial.PARITY_ODD)

timeout = 1：串口读取数据特别慢
timeout = 0.01：串口读取数据正常

吓得我赶紧查看下官方文档：

timeout = None: wait forever / until requested number of bytes are received
timeout = 0: non-blocking mode, return immediately in any case, returning zero or more, up to the requested number of bytes
timeout = x: set timeout to x seconds (float allowed) returns immediately when the requested number of bytes are available, otherwise wait until the timeout expires and return all bytes that were received until then.

显然，我个人用的就是第三种赋值方法，这个解释就是：在设定的timeout时间范围内，如果读取的字节数据是有效的（就是非空）那就直接返回，否则一直会等到这个设定的timeout时间并返回这段时间所读的全部字节数据。

分析下代码：

#read data
def ReadData(self,timeDelay):
    bReadData = False
    for i in range(0, 5, 1):
        time.sleep(timeDelay)
        readString = self.ser.readline()
        if(len(readString) > 1):
            return readString
        else:
            continue
    if(bReadData == False):
        return "fail"

发现读取数据用的是readline()这个函数，那具体实现机制会是怎样呢，个人理解如下：

1、Python2的内置编码是ASCII码

2、官方文档给出的解释是针对一串字符串而言，但readline()函数的操作对象肯定是单字节

3、单字节在读取的时候是有一定的时间间隔的，即读完一个字节隔段时间再读一个字节

4、这个时间间隔很有可能和timeout值成正比