Upload Problem: touching COM with 1200 baud rate cannot reset all the board on Windows 7.

Hi,
Our customer, a teacher, bought a bunch of Arduino 101 from us. However About half of Arduino 101 fail to upload the sketch through the computer in his school (Windows 7), while another half can work properly. By the way all the computers can upload sketches to Arduino Uno.

The other interesting thing is his own laptop with windows 10 can always upload successfully.

After remote assistance with Teamviewer, we found the issue that touching serial port with 1200 cannot reset the Arduino 101, which prevents the upload process. If we reset the board manually when uploading, it works like charm.

We know refresh installing Windows can deal with the problem. However in school there are hundreds of PC. The deployment cost is too high for them. Could you try to research into this problem? We are delighted to help you dealing with this problem. Thank you

OS: Windows 7 x64
What we have done:
* Uninstall and reinstall the Serial port driver and DFU driver.
* Replace the driver files like usbser.sys, mdmcpq.inf, mdmcpq.PNF in Windows.
* Use CoolTerm to connect the COM with 1200 baud.

Best regards
Angelo

No source files or tests are identified. Start by reproducing the Arduino 101 upload flow that touches the serial port at 1200 baud on Windows 7, comparing the failing boards with Arduino Uno and Windows 10; done means the board resets reliably and uploads without a manual reset.

Written by the indexing model from the issue text.