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Ubuntu 更新后串行端口无法正常工作？

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Ubuntu 更新后串行端口无法正常工作？

我的串行端口出现了一个奇怪的问题。Ubuntu 更新和重启后，似乎发生了一些变化。

przem@przem:~/Pulpit/bat/scripts$ python
Python 2.7.6 (default, Jun 22 2015, 17:58:13) 
[GCC 4.8.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import serial
>>> ser = serial.Serial("/dev/ttyUSB0", 57600)
>>> ser.read()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python2.7/dist-packages/serial/serialposix.py", line 475, in read
    raise SerialException('device reports readiness to read but returned no data (device disconnected or multiple access on port?)')
serial.serialutil.SerialException: device reports readiness to read but returned no data (device disconnected or multiple access on port?)
>>>

我知道我的设备应该返回“ ”（空符号）的结果，但是我得到的却不是这个结果，而是异常：

“设备报告读取准备就绪但未返回任何数据（设备断开连接或端口上有多个访问？）”

这个问题是我的问题的介绍：https://stackoverflow.com/questions/32844942/serialport-doenst-work-correctly-after-ubuntu-update?noredirect=1#comment53527004_32844942

请帮我。

答案1

我遇到了同样的问题。它似乎不仅限于串行端口硬件。您可以使用 socat 创建两个伪终端：

$ socat -d -d pty,raw,echo=0 pty,raw,echo=0
2015/09/30 09:46:18 socat[6296] N PTY is /dev/pts/17
2015/09/30 09:46:18 socat[6296] N PTY is /dev/pts/18
2015/09/30 09:46:18 socat[6296] N starting data transfer loop with FDs [3,3] and [5,5]

您可以同时连接两个设备，例如使用 cu

cu -l /dev/pts/17 -s 115200

和

cu -l /dev/pts/18 -s 115200

并双向发送数据，没有问题。

但连接 Python 2.7 失败，并出现您提到的错误消息

$ python
Python 2.7.6 (default, Jun 22 2015, 17:58:13) 
[GCC 4.8.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import serial
>>> ser = serial.Serial("/dev/pts/17", 230400, timeout=0.2)
>>> ser.read()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.7/dist-packages/serial/serialposix.py", line 460, in read
    raise SerialException('device reports readiness to read but returned no data (device disconnected?)')
serial.serialutil.SerialException: device reports readiness to read but returned no data (device disconnected?)

此代码在昨天安装 Ubuntu 14.04 更新之前有效。

有任何想法吗？

答案2

我不赞同这样做，但在做出这个改变之后，我不再看到这些错误：

--- serialposix.py.stock    2015-10-03 06:53:45.241261071 -0700 
+++ serialposix.py  2015-10-03 06:55:07.481262475 -0700
@@ -457,7 +457,11 @@
             # Disconnected devices, at least on Linux, show the
             # behavior that they are always ready to read immediately
             # but reading returns nothing.
-                raise SerialException('device reports readiness to read but returned no data (device disconnected?)')
+                # retrying the read seems to get me past this error:
+                # [ERROR] Can't read from printer (disconnected?)     (SerialException): device reports readiness to read but returned no data (device disconnected?)
+
+                #raise SerialException('device reports readiness to read but returned no data (device disconnected?)')
+                pass
         read.extend(buf)
     return bytes(read)

答案3

这可能是内核错误。请参见此处：https://bugs.launchpad.net/ubuntu/+source/python2.7/+bug/1501240

解决方法似乎是使用内核3.13.0-63-generic。

您可以在启动时按住 shift 键来更改一次性启动的内核。要使更改持久化，您需要编辑/etc/default/grub：https://askubuntu.com/questions/262965/grub-timeout-set-to-0-cant-access-grub-menu-anymore?rq=1

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