DOCUMENT:Q199528  04-MAY-2001  [visualc]
TITLE   :BUG: CEPC Mouse Driver Moves Cursor Erratically
PRODUCT :Microsoft C Compiler
PROD/VER:N\A:2.11,2.12; WINDOWS:1.0
OPER/SYS:
KEYWORDS:kbVC500bug kbOSWinCEsearch kbOSWinCE211bug kbOSWinCE212bug

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The information in this article applies to:

 - Microsoft Windows CE 2.10 Enhancement Pack for Windows CE Embedded Toolkit for Visual C++ 5.0 
 - Microsoft Windows CE Platform Builder, versions 2.11, 2.12 
 - Microsoft Windows CE Embedded Toolkit for Visual C++ 5.0, version 1.0 
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SYMPTOMS
========

The mouse cursor on the PC-based reference platform (CEPC) may move erratically
on some hardware combinations or if the mouse is moved while the system is
starting (on any hardware platform).

CAUSE
=====

Mouse movement data arrives in fixed-length packets from the mouse hardware. If
the alignment of the packets in the data stream becomes out of sync with the
alignment the driver is expecting, the driver will misinterpret the mouse data.
For example, movement information will be interpreted as button status, and
button status will be interpreted as movement data.

The KBDMOUSE driver in Windows CE 2.11 for the x86 CEPC platform does contain
code to resynchronize the mouse packets. However, due to a code defect, this
part of the mouse driver does not function as intended.

RESOLUTION
==========

The following modification to the KBDMOUSE sample driver will correct the
problem.

In Ps2mouse.cpp, modify the function Ps2Mouse::IsrThreadProc as follows:

1. Remove, in its entirety, the first if/else clause that follows the
   wait_for_interrupt label.

2. Modify the next if statement to read as follows:

   if ( WaitForSingleObject(m_hevInterrupt, (cBytes == 0) ? INFINITE : INPACKET_TIMEOUT) == WAIT_TIMEOUT )
   			{
   			cBytes = 0;
   			goto wait_for_interrupt;
   			}

3. Remove references to variables bInPacket and cmsInPacketTimeout.

4. Modify Ps2mouse.hpp to include:

   #define INPACKET_TIMEOUT  50

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article. The correction to this problem is given in the
RESOLUTION section of this article.

MORE INFORMATION
================

Mouse data arrives from the device in 3-byte packets. Each packet contains x and
y movement data and a button-status byte. The mouse driver must synchronize the
data at mouse reset and then keep a count of 3-byte packets.

The synchronization problem in the CEPC KBDMOUSE sample driver occurs when the
mouse port has data in the input buffer after the mouse is initialized. This
data is interpreted as the first byte of a mouse data packet, and so the first 2
bytes of the next mouse packet are interpreted as the second and third bytes of
a packet. All subsequent packets are misinterpreted in the same way.

Additional query words: kbDSupport

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Keywords          : kbVC500bug kbOSWinCEsearch kbOSWinCE211bug kbOSWinCE212bug 
Technology        : kbAudDeveloper kbSDKSearch kbWinCEETKSearch kbWinCESDKSearch kbWinCESearch kbWinCESDK211 kbWinCESDK212 kbWinCEEnh210ETKVC500 kbWinCEETKVC500
Version           : N\A:2.11,2.12; WINDOWS:1.0
Issue type        : kbbug
Solution Type     : kbfix

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