FIX: CV 4.0 Port Input Command Does Not Display Value

The information in this article applies to:

• Microsoft CodeView for MS-DOS, versions 4.0, 4.01, 4.05

SYMPTOMS

The Port Input (I) command should display the byte from the specified hardware port. This feature does not work correctly in Microsoft CodeView versions 4.0, 4.01, and 4.05.

(Note: This command is only valid under MS-DOS. Under Windows, it should be ignored, and as a result does not display a value.)

RESOLUTION

You can write a function that will achieve the same result. The following is an example. To use it to check port 2f0h, type "?in(0x2f0)" at the CodeView command prompt.

   #pragma check_stack(off)
   unsigned in( unsigned x ) {
      _asm {
         push dx             // save register
         mov  dx, x
         in   ax, dx
         pop  dx             // restore register
         }
   }                         //
   #pragma check_stack()

STATUS

Microsoft has confirmed this to be a problem in CodeView versions 4.0, 4.01, and 4.05. This problem was corrected in CodeView version 4.1.