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Q107696: Modifying COMM.DRV to Support up to Nine Ports

Article: Q107696
Product(s): Microsoft Windows Device Driver Kit
Version(s): 3.1
Operating System(s): 
Keyword(s): 
Last Modified: 03-NOV-1999

-------------------------------------------------------------------------------
The information in this article applies to:

- Microsoft Windows Device Development Kit (DDK) for Windows, version 3.1 
-------------------------------------------------------------------------------

SUMMARY
=======

The Windows 3.1 communications application programming interface (API) supports
up to nine communications (COM) ports. However, COMM.DRV that is included with
Windows 3.1 handles only four COM ports. With the Windows 3.1 DDK, COMM.DRV can
be modified to handle up to nine ports. This information is specific to COMM.DRV
for Windows 3.1 and Windows for Workgroups 3.1.


Please note: If a system has more than four COM ports, it probably has a
nonstandard multiport serial board, which will require more extensive changes
than listed below. Contact the hardware vendor to see if a modified
communications driver already exists for the specific hardware.

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

The Windows DDK contains the source for COMM.DRV. The necessary changes to
support nine COM ports are listed below. Also, a few lines must be added to
SYSTEM.INI.

In the [386Enh] section of SYSTEM.INI, the following entries must be made:

  COMxBASE = address - "x" is the COM port number, and "address" is the base
  port address for the port.

  COMxIrq = number - "x" is the COM port number, and "number" is the IRQ used by
  the port.

  MaxCOMPort = number - "number" is the maximum number of COM ports supported in
  386 enhanced mode.

Below are the changes that must be made to the COMM.DRV source. Please remember
that by modifying the source, the driver is no longer a Microsoft product, and
therefore the name of the driver must be changed. However, do not change the
module name; it must be COMM.

The following changes are shown in comparison to the original files. These files
are contained in the \286\COMM subdirectory of the Windows 3.1 DDK.

This change notifies COMM.DRV that there are nine ports:

Comparing Files IBMCOM.INC and \COMM\IBMCOM.INC
-----------------------------------------------

IBMCOM.INC

  11:  MAXLPT   equ   2        ;Three LPTs supported (LPT1, 2 ,3)
  12:  MAXCOM   equ   8        ;Nine COMs supported
  13:

\COMM\IBMCOM.INC

  11:  MAXLPT   equ   2        ;Three LPTs supported (LPT1, 2 ,3)
  12:  MAXCOM   equ   3        ;Four COMs supported (COM1, 2, 3, 4)
  13:

This change fixes a bug that occurs when COM ports are sharing IRQs. For more
information on this bug, query on the following words in the Microsoft Knowledge
Base:

  " sharing and IRQ and COM1 and reboot " (without the quotation marks)


Comparing Files IBMSETUP.ASM and \COMM\IBMSETUP.ASM
---------------------------------------------------

IBMSETUP.ASM

 142:
 143:  Dummy   dw      0         ; Make sure COM1 is not 0!
 144:

\COMM1\IBMSETUP.ASM

 142:
 143:

Change the version, so this version of the driver is identified as the nine- port
version:

Comparing Files COMM.RCV and \COMM\COMM.RCV
-------------------------------------------

COMM.RCV

  10:  #define VER_FILESUBTYPE          VFT2_DRV_COMM
  11:  #define VER_FILEDESCRIPTION_STR  "Windows COMM Driver - 9 Port Ver"
  12:  #define VER_INTERNALNAME_STR     "COMM"

\COMM1\COMM.RCV

  10:  #define VER_FILESUBTYPE           VFT2_DRV_COMM
  11:  #define VER_FILEDESCRIPTION_STR   "Windows COMM Driver"
  12:  #define VER_INTERNALNAME_STR      "COMM"

There are a few jumps here that are "short" in the retail COMM.DRV. Because of
the changes, they need to be changed to "near".

Comparing Files IBMINT.ASM and \COMM\IBMINT.ASM
-----------------------------------------------

IBMINT.ASM

 147:          mov     di, DataOFFSET IRQhook&num
 148:          jmp     NEAR PTR DEF_RM_Handler
 149:  DEF_RM_COM_INT_&num endp

\COMM1\IBMINT.ASM

 147:          mov     di, DataOFFSET IRQhook&num
 148:          jmp     short DEF_RM_Handler
 149:  DEF_RM_COM_INT_&num endp

IBMINT.ASM

 155:          mov     di, DataOFFSET IRQhook&num
 156:  IF MAXCOM-num LE 4
 157:          jmp     short DEF_Handler
 158:  ELSE
 159:          jmp NEAR PTR DEF_Handler
 160:  ENDIF
 161:  DEF_COM_INT_&num endp

\COMM1\IBMINT.ASM

 155:          mov     di, DataOFFSET IRQhook&num
 156:          jmp     short DEF_Handler
 157:  DEF_COM_INT_&num endp

IBMINT.ASM

 177:          mov     di, DataOFFSET IRQhook1
 178:          jmp     NEAR PTR DEF_RM_Handler
 179:  DEF_RM_COM_INT_1 endp

\COMM1\IBMINT.ASM

 173:          mov     di, DataOFFSET IRQhook1
 174:          jmp     short DEF_RM_Handler
 175:  DEF_RM_COM_INT_1 endp

Additional query words: 3.10 COMM.DRV 9 PORT

======================================================================
Keywords          :  
Technology        : kbAudDeveloper kbWin3xSearch kbWinDDKSearch kbWinDDK310
Version           : :3.1

=============================================================================

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