Digital clock for my PC XT compatible, or having fun with Borland Graphics Interface (BGI)

Yet another day “wasted” playing with my Pravetz 16. Really I should sit on my … and do some real work, but the battery of my wall clock died and I decided to code myself a digital one 🙂

The clock in action
The clock in action

The clock is written on C using Borland Graphics Interfaces also knows as BGI. The most easy and video hardware independent option for doing graphics under DOS. BGI comes bundled with drivers for common back then graphic adapters (CGA, VGA and EGA) and vector fonts.

There are other options such as using interrupt 10h or writing directly to the graphics hardware like most of the games were doing back then.

To build the code fire up the Turbo C IDE, go to Options->Linker and check “Graphics library”, then proceed as usual.

Turbo C Linker options
Turbo C Linker options

Compiled version of the CLOCK.EXE can be obtained from here and the source code (if you don’t like Ctrl + C & Ctrl + V) is here.

Wen I got some free time and motivation I will probably enhance the clock with some neat options such as 12/24 hours mode, moving objects in the background, drawing the “Pravetz” logo in the upper left corner of the screen, command line parameters for setting an alarm etc…

If you wan’t to learn more about BGI review the examples that comes with Turbo C such as BARCHART.C. View the GRAPHICS.H header. Also take a look here.

Code listing a.k.a “The Digital Clock” source 🙂

#include <stdio.h>
#include <dos.h>
#include <graphics.h>
 
#define TIME_BUF_LEN 6
#define DATE_BUF_LEN 10
 
#define TIME_TEXT_TEMPLATE "00:00"
#define DATE_TEXT_TEMPLATE "00.00.0000"
 
#define NOTE_TEXT "Press any key to exit..."
 
#define BGI_LOCATION "C:\\TC\\bgi"
 
int gl_nMaxX = 0;
int gl_nMaxY = 0;
 
int gl_nCenterX = 0;
int gl_nCenterY = 0;
 
char gl_szTimeBuff[TIME_BUF_LEN];
char gl_szDateBuff[DATE_BUF_LEN];
 
int initGraphics( void )
{
	int nGraphicDriver = DETECT; 
	int nGraphMode;
	int nErrorCode;
 
	/* Initialize graphics system */
	initgraph(&nGraphicDriver, &nGraphMode, BGI_LOCATION);
	nErrorCode = graphresult();
 
	if (nErrorCode != grOk)
	{
	   return -1;
	}        
 
	/* Graphics OK, so return "true" */
	return 1; 
}
 
void drawNote()
{
	int textWidth, textHeight;
 
	settextstyle(DEFAULT_FONT, HORIZ_DIR, 0);
 
	textWidth = textwidth(NOTE_TEXT);
	textHeight = textheight(NOTE_TEXT);
 
	outtextxy(gl_nMaxX - textWidth,
			  gl_nMaxY - textHeight,
			  NOTE_TEXT);
}
 
void drawTime(struct time *pTime)
{
	int textWidth, textHeight;
 
	settextstyle(SANS_SERIF_FONT, HORIZ_DIR, 8);
 
	textWidth = textwidth(TIME_TEXT_TEMPLATE);
	textHeight = textheight(TIME_TEXT_TEMPLATE);
 
	sprintf(gl_szTimeBuff, "%02d:%02d", pTime->ti_hour, pTime->ti_min);
 
	outtextxy(gl_nCenterX - (textWidth / 2), 
			  gl_nCenterY - textHeight, 
			  gl_szTimeBuff);
}
 
void drawDate(struct date *pDate)
{
	int textWidth;
 
	settextstyle(SANS_SERIF_FONT, HORIZ_DIR, 6);
 
	textWidth = textwidth(DATE_TEXT_TEMPLATE);
 
	sprintf(gl_szDateBuff, 
			"%02d.%02d.%d", 
			pDate->da_day, 
			pDate->da_mon, 
			pDate->da_year);
 
	outtextxy(gl_nCenterX - (textWidth / 2), gl_nCenterY, gl_szDateBuff);
}
 
int main(void)
{
	struct time sysTime, startTime;
	struct date sysDate, startDate;	
 
	if(initGraphics() == -1)
	{
		printf("Error initializing BGI!\n");
		return 0;
	}
 
	gl_nMaxX = getmaxx();
	gl_nMaxY = getmaxy();
 
	gl_nCenterX = (getmaxx() / 2);
	gl_nCenterY = (getmaxy() / 2);		
 
	drawNote();
 
	gettime(&startTime);
	drawTime(&startTime);
 
	getdate(&sysDate);
	drawDate(&sysDate);
 
	while(!kbhit())
	{										
		gettime(&sysTime);
 
		/*
		 * To avoid flickering, redraw the screen only if there are 
		 * changes in the hour or minute values. Only some VGA and EGA
		 * drivers support 'setactivepage()' and 'setvisualpage()'.
		 */
		if(sysTime.ti_hour > startTime.ti_hour || 
		   sysTime.ti_min > startTime.ti_min)
		{
			cleardevice();
			getdate(&sysDate);
 
			drawNote();
			drawTime(&sysTime);
			drawDate(&sysDate);
 
			gettime(&startTime);
		}
	}
 
	closegraph();
 
	return 0;
}

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

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 &amp; 0x0001) ? "yes" : "no");
 
  if((systemInfo &amp; 0x0001))
  {
    switch((systemInfo &amp; 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 &amp; 0x0002) ? "yes" : "no");
 
  mem = (systemInfo &amp; 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 &gt;= 256) ? "+" : " ");
  printf("Memory reported by BIOS POST: %dK\n", memSizePost);
 
  videoMode = (systemInfo &amp; 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 &amp; 0x0100) == 0 ? "yes" : "no");
  printf("Game adapter: %s\n", (systemInfo &amp; 0x1000) == 0 ? "no" : "yes");
 
  switch((systemInfo &amp; 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 &amp; 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;
}