AnsweredAssumed Answered

USB virtual COM port hot plug problem

Question asked by yang.shuozhi on Oct 17, 2012
Latest reply on Jan 21, 2014 by rocketdawg
Hi,


I have a problem while developing a USB-to-serial device and I am looking for a solution.


I successfully implemented a USB virtual COM port on STM32F407 microcontroller. I can send and receive data to/from the computer via hyperterminal program perfectly using the generic virtual COM driver provided by Windows 7. However, if I unplug the USB cable while Hyperterminal is still in "connected" state, the communication cannot be established when I plug it back. To resume the communication, I have to 1. disconnect Hyperterminal, 2. unplug USB cable, 3. plug it back again and then 4. connect Hyperterminal.


To clarify the situation I am in, here are two senarios:


Senario 1:
- plug USB cable
- connect Hyperterminal
- communication established successfully and worked well
- disconnect Hyperminal
- unplug USB cable
- plug USB cable back 
- connect Hyperterminal
- communication established successfully and worked well


Senario 2:
- plug USB cable
- connect Hyperterminal
- communication established successfully and worked well
- unplug USB cable
- plug USB cable back 
- Hyperminal not working (but Windows device manager sees the disappearance and reappearance of the virtual COM port)
- disconnect Hyperminal
- connect Hyperterminal (FAIL! Hyperterminal cannot connect to this virtual COM port even if device manager has it in the COM port list)
- unplug USB cable (now Hyperterminal is in disconnected state)
- plug USB cable
- connect Hyperterminal
- communication established successfully and worked well


I captured the USB traffic with SourceUSB and found that when I tried to disconnect Hyperterminal in Senario 2, it said "No such device".


Any suggestions are appreciated! Thanks!




Shuozhi

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