PRB: CTRL+BREAK, CTRL+ALT+SYSRQ, CTRL+C Do Not Return Control

The information in this article applies to:

• Microsoft CodeView for MS-DOS versions 4.0, 4.01, 4.05, and 4.1

SYMPTOMS

When debugging an MS-DOS program using CodeView 4.0, 4.01, 4.05, or 4.1 the CTRL+C, CTRL+BREAK, and CTRL+ALT+SYSRQ key combinations do not return control to CodeView as they do with earlier CodeView versions.

CAUSE

This behavior is by design. The DPMI server (Windows or 386MAX) traps these interrupts for other purposes.

MORE INFORMATION

There are three ways to work around this limitation.

• Run CodeView outside of Windows and without 386MAX loaded. Without a DPMI server, the break should occur normally. Drivers like HIMEM, EMM386, and QEMM can be used to provide access to extended memory. Note that if EMM386.EXE is used, VCPI memory is provided and the recommended settings for EMM386.EXE change when running CodeView without Windows. Uncomment the following line in the CONFIG.SYS file to change the settings accordingly, or remove EMM386.EXE (then HIMEM will provide XMS memory)

        rem device=c:\windows\emm386.exe m9 2048 ram
  

  Note that 2048 might be too low a setting in some cases.

• Set strategic breakpoints in your code to force return of control.
• Break when you know an MS-DOS function is being called. During an MS-DOS interrupt, breaks should occur normally.