Example of How to Call Basic SetUEvent from C; ON UEVENT GOSUB (69159)

MORE INFORMATION

Use the following command to compile the C program listed below:

   CL -Od -AM -c uevent.c
				

Use the following command to compile the Basic program listed below:

   BC /O/V Basic.BAS;
				

Link the programs together with the following command:

   LINK /NOE Basic+UEVENT, UEVENT.EXE;
				

When the program is executed, the line "Arrived here after 4.5 seconds" will print every 4.5 seconds.

Note: The C program must be compiled with the medium memory model because the DS register must point to Basic's DGROUP space when SetUEvent is called.

Basic Code Example, Basic.BAS

' To try this example in VBDOS.EXE:
' 1. From the File menu, choose New Project.
' 2. Copy the code example to the Code window.
' 3. Press F5 to run the program.

DECLARE SUB SetInt
DECLARE SUB RestInt
 
' Install new interrupt service routine:
CALL SetInt
' Set up the Basic event handler:
ON UEVENT GOSUB SpecialTask
UEVENT ON
 
DO
' Normal program operation occurs here.
' Program ends when any key is pressed.
LOOP UNTIL INKEY$ <> ""
 
' Restore old interrupt service routine before quitting:
CALL RestInt
END
 
' Program branches here every 4.5 seconds:
SpecialTask:
' Code for special task goes here, for example:
PRINT "Arrived here after 4.5 seconds"
RETURN

				

C Code Example, UEVENT.C

' To try this example in VBDOS.EXE:
' 1. From the File menu, choose New Project.
' 2. Copy the code example to the Code window.
' 3. Press F5 to run the program.

DECLARE SUB SetInt
DECLARE SUB RestInt
' Install new interrupt service routine:
CALL SetInt
' Set up the Basic event handler:
ON UEVENT GOSUB SpecialTask
UEVENT ON

DO
' Normal program operation occurs here.
' Program ends when any key is pressed.
LOOP UNTIL INKEY$ <> ""

' Restore old interrupt service routine before quitting:
CALL RestInt
END

' Program branches here every 4.5 seconds:
SpecialTask:
' Code for special task goes here, for example:
PRINT "Arrived here after 4.5 seconds"
RETURN
				

C Code Example, UEVENT.C

#include <dos.h>
extern pascal SetUEvent();           // Define SetUEvent, which is in
                                     // the Basic run-time library.
void (_interrupt _far *OldInt) (void);    // The old interrupt vector.
void _interrupt _far EventHandler (void);       // The UEVENT handler.
char TimerTicks = 0;                      // Number of ticks elapsed.

void pascal SetInt()                      // Set up the interrupts
{                                         //   to point to the UEVENT
    OldInt = _dos_getvect(0x1C);          //    handler.
    _dos_setvect(0x1C, EventHandler);
}

void interrupt EventHandler()            // This is the UEVENT handler.
{
        if (++TimerTicks > 82)           // Check to see if 4.5 seconds
      {                                  //    has elapsed (18.2
        TimerTicks = 0;                  //    ticks = 1 second).
        SetUEvent();
      }
    _chain_intr(OldInt);                // Continue through old
}                                       //    interrupt routine.

void pascal RestInt()                   // Restore old interrupt
{                                       //    when done to avoid
    _dos_
setvect(0x1C, OldInt);         //    conflicts after exit.
}