pyserial - 如何读取从串行设备发送的最后一行 [英] pyserial - How to read the last line sent from a serial device

问题描述

我有一个 Arduino 连接到我的计算机运行循环，每 100 毫秒通过串行端口向计算机发送一个值.

I have an Arduino connected to my computer running a loop, sending a value over the serial port back to the computer every 100 ms.

我想制作一个 Python 脚本，每隔几秒钟从串口读取一次数据，所以我希望它只看到从 Arduino 发送的最后一件事.

I want to make a Python script that will read from the serial port only every few seconds, so I want it to just see the last thing sent from the Arduino.

你如何在 Pyserial 中做到这一点?

How do you do this in Pyserial?

这是我试过但不起作用的代码.它按顺序读取行.

Here's the code I tried which does't work. It reads the lines sequentially.

import serial
import time

ser = serial.Serial('com4',9600,timeout=1)
while 1:
    time.sleep(10)
    print ser.readline() #How do I get the most recent line sent from the device?

推荐答案

也许我误解了您的问题，但由于它是串行线路，您必须按顺序读取从 Arduino 发送的所有内容 - 它会被缓冲在 Arduino 中，直到您阅读它.

Perhaps I'm misunderstanding your question, but as it's a serial line, you'll have to read everything sent from the Arduino sequentially - it'll be buffered up in the Arduino until you read it.

如果你想有一个状态显示来显示最新发送的东西 - 使用一个线程在你的问题中包含代码(减去睡眠)，并保持最后一行作为来自 Arduino 的最新行读取.

If you want to have a status display which shows the latest thing sent - use a thread which incorporates the code in your question (minus the sleep), and keep the last complete line read as the latest line from the Arduino.

更新: mtasic 的示例代码相当不错，但是如果 Arduino 在调用 inWaiting() 时发送了部分行，你会得到一条截断的线.相反，您想要做的是将最后的 complete 行放入 last_received 中，并将部分行保留在 buffer 中，以便它可以附加到下一次循环.像这样:

Update: mtasic's example code is quite good, but if the Arduino has sent a partial line when inWaiting() is called, you'll get a truncated line. Instead, what you want to do is to put the last complete line into last_received, and keep the partial line in buffer so that it can be appended to the next time round the loop. Something like this:

def receiving(ser):
    global last_received

    buffer_string = ''
    while True:
        buffer_string = buffer_string + ser.read(ser.inWaiting())
        if '\n' in buffer_string:
            lines = buffer_string.split('\n') # Guaranteed to have at least 2 entries
            last_received = lines[-2]
            #If the Arduino sends lots of empty lines, you'll lose the
            #last filled line, so you could make the above statement conditional
            #like so: if lines[-2]: last_received = lines[-2]
            buffer_string = lines[-1]

关于 readline() 的使用:以下是 Pyserial 文档的说明(为清晰起见略作编辑，并提及 readlines()):

Regarding use of readline(): Here's what the Pyserial documentation has to say (slightly edited for clarity and with a mention to readlines()):

使用readline"时要小心.做打开时指定超时串口，否则会阻塞如果没有换行符，则永远已收到.还要注意readlines()"仅适用于超时.它取决于超时和将其解释为 EOF(文件结尾).

Be careful when using "readline". Do specify a timeout when opening the serial port, otherwise it could block forever if no newline character is received. Also note that "readlines()" only works with a timeout. It depends on having a timeout and interprets that as EOF (end of file).

这对我来说似乎很合理！

which seems quite reasonable to me!

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