Tag Archives: dosbox

SINFO.EXE or playing with bios interrupts on my PC XT clone

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I am stuck with a problem in the game I work on for several days now. When I’m stuck I usually do something else for a couple of hours. For example playing with bios interrupts on my PC XT clone (which by the way is completely restored, but more on this in the upcoming posts).

Pravetz 16 (IBM PC XT clone)

Pravetz 16 (IBM PC XT clone) and yes that’s Windows 3.0.

NOTE: Writing code on monochrome monitor is something that every software developer should do at least ones in his career 🙂

What’s interrupt? (From Wikipedia articles on interrupts)

In system programming, an interrupt is a signal to the processor emitted by hardware or software indicating an event that needs immediate attention. An interrupt alerts the processor to a high-priority condition requiring the interruption of the current code the processor is executing. The processor responds by suspending its current activities, saving its state, and executing a function called an interrupt handler (or an interrupt service routine, ISR) to deal with the event. This interruption is temporary, and, after the interrupt handler finishes, the processor resumes normal activities.[1] There are two types of interrupts: hardware interrupts and software interrupts.

The code below calls software interrupts 11h (Equipment Installed) and 12h (Memory Available) using inline assembly. To compile the source you will need Turbo C and TASM. They both run perfectly fine under DOSBox.

The executable is available for download here.

#include 
 
int main(void)
{
  int systemInfo;
  int floppyCount;
  int mem, memSize, memSizePost;
  int videoMode;
  int serialPorts;
  int paralelPorts;
 
  /* Call INT 11h ( Equipment Installed ) */
  asm int 11h;
  asm mov systemInfo, ax;
 
  /* Call INT 12h ( Memory Available ) */
  asm int 12h;
  asm mov memSizePost, ax;
 
  printf("********** SYSTEM INFO ***********\n");
  printf("Floppy drive(s): %s ", (systemInfo & 0x0001) ? "yes" : "no");
 
  if((systemInfo & 0x0001))
  {
    switch((systemInfo & 0x00C0))
    {
      case 0:
      {
		floppyCount = 1;
		break;
      }
      case 64:
      {
		floppyCount = 2;
		break;
      }
      case 128:
      {
		floppyCount = 3;
		break;
      }
      case 192:
      {
		floppyCount = 4;
		break;
      }
    }
 
    printf("(%d)\n", floppyCount);
  }
  else
  {
    printf("\n");
  }
 
 
  printf("Math co-processor: %s\n", (systemInfo & 0x0002) ? "yes" : "no");
 
  mem = (systemInfo & 0x000C);
 
  switch(mem)
  {
    case 0:
    {
      memSize = 16;
      break;
    }    
    case 4:
    {
      memSize = 32;
      break;
    }
    case 8:
    {
      memSize = 48;
      break;
    }
    case 12:
    {
      memSize = 256;
      break;
    }
  }
  printf("On-board memory: %d K%s\n", memSize, (memSize >= 256) ? "+" : " ");
  printf("Memory reported by BIOS POST: %dK\n", memSizePost);
 
  videoMode = (systemInfo & 0x0030);
  switch(videoMode)
  {
    case 0:
    {
      printf("Video mode: EGA, VGA or PGA\n");
      break;
    }
    case 16:
    {
      printf("Video mode: CGA, 40 x 25\n");
      break;
    }
    case 32:
    {
      printf("Video mode: CGA, 80 x 25\n");
      break;
    }
    case 48:
    {
      printf("Video mode: monochrome, 80 x 25\n");
      break;
    }
  }
 
  printf("DMA support: %s\n", (systemInfo & 0x0100) == 0 ? "yes" : "no");
  printf("Game adapter: %s\n", (systemInfo & 0x1000) == 0 ? "no" : "yes");
 
  switch((systemInfo & 0x0E00))
  {
    case 0:
    {
      serialPorts = 0;
      break;
    }
    case 512:
    {
      serialPorts = 1;
      break;
    }
    case 1024:
    {
      serialPorts = 2;
      break;
    }
    case 1536:
    {
      serialPorts = 3;
      break;
    }
    case 2048:
    {
      serialPorts = 4;
      break;
    }
  }
  printf("Serial ports: %d\n", serialPorts);
 
  switch((systemInfo & 0xC000))
  {
    case 0:
    {
      paralelPorts = 0;
      break;
    }
    case 16384:
    {
      paralelPorts = 1;
      break;
    }
    case 32768:
    {
      paralelPorts = 2;
      break;
    }
    case 49152:
    {
      paralelPorts = 3;
      break;
    }
  }
  printf("Paralel ports: %d\n", paralelPorts);
 
  return 0;
}