PySerial could not open port COM4: [Error 5] Access is denied - please help

[Grant Edwards]

On 2012-06-27, David H. Lipman <DLipman~nospam~@Verizon.Net> wrote:
> From: "Adam" <adam at no_thanks.com>
>> "John Nagle" <nagle at animats.com> wrote in message 
>> news:jse604$1cq$1 at dont-email.me...
>>> On 6/26/2012 9:12 PM, Adam wrote:
>>>> Host OS:    Ubuntu 10.04 LTS
>>>> Guest OS:    Windows XP Pro SP3
>>>>
>>>> I am able to open port COM4 with Terminal emulator.
>>>>
>>>> So, what can cause PySerial to generate the following error ...
>>>>
>>>> C:\Wattcher>python wattcher.py
>>>> Traceback (most recent call last):
>>>>    File "wattcher.py", line 56, in <module>
>>>>      ser.open()
>>>>    File "C:\Python25\Lib\site-packages\serial\serialwin32.py", line 56, in open
>>>>      raise SerialException("could not open port %s: %s" % (self.portstr,
>>>> ctypes.WinError()))
>>>> serial.serialutil.SerialException: could not open port COM4: [Error 5]
>>>> Access is denied.
>>>
>>> Are you trying to access serial ports from a virtual machine? Which
>>> virtual machine environment?  Xen?  VMware? QEmu?  VirtualBox? I
>>> wouldn't expect that to work in most of those.

Except he says it _does_ work with his terminal emulator.

>>> What is "COM4", anyway?   Few machines today actually have four
>>> serial ports.  Is some device emulating a serial port?

It shouldn't matter.  If other apps can open COM4, then pyserial
should be able to open COM4.

>> Thanks, and yes, I am using VirtualBox.  My laptop does not have a
>> serial port so I use a USB-to-serial converter, which is assigned
>> COM4.
>
> Then it is a Virtual COM port. Often software will want to
> communicate directly to the COM4 port which is usually at: IRQ3 and
> I/O 2E8h.

Pyserial doesn't do that.  It uses the standard win32 serial API, and
it should work just fine with any Win32 serial device (what you call a
"virtual" COM port).

-- 
Grant Edwards               grant.b.edwards        Yow! World War III?
                                  at               No thanks!
                              gmail.com