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#include <kernel.h>

#define   VGA_AC_INDEX          0x3C0
#define   VGA_AC_WRITE          0x3C0
#define   VGA_AC_READ           0x3C1
#define   VGA_MISC_WRITE        0x3C2
#define   VGA_SEQ_INDEX         0x3C4
#define   VGA_SEQ_DATA          0x3C5
#define   VGA_DAC_READ_INDEX    0x3C7
#define   VGA_DAC_WRITE_INDEX   0x3C8
#define   VGA_DAC_DATA          0x3C9
#define   VGA_MISC_READ         0x3CC
#define   VGA_GC_INDEX          0x3CE
#define   VGA_GC_DATA           0x3CF
#define   VGA_CRTC_INDEX        0x3D4      /* 0x3B4 */
#define   VGA_CRTC_DATA         0x3D5      /* 0x3B5 */
#define   VGA_INSTAT_READ       0x3DA
#define   VGA_NUM_SEQ_REGS      5
#define   VGA_NUM_CRTC_REGS     25
#define   VGA_NUM_GC_REGS       9
#define   VGA_NUM_AC_REGS       21
#define   VGA_NUM_REGS         (1+VGA_NUM_SEQ_REGS+VGA_NUM_CRTC_REGS+VGA_NUM_GC_REGS+VGA_NUM_AC_REGS)

//the vga identifiers
unsigned int VGA_width;
unsigned int VGA_height;
unsigned int VGA_bpp;
unsigned char *VGA_address;

void VGA_init(int width, int height, int bpp);
void write_registers(unsigned char *regs);

void vga_mode()
{
	VGA_init(640,480,16);
}

/*
 * Create Register Array
 */

unsigned char g_640x480x16[] =
{
/* MISC */
	0xE3,
/* SEQ */
      0x03, 0x01, 0x0F, 0x00, 0x02,

/* CRTC */
	0x5F, 0x4F, 0x50, 0x82, 0x54, 0x80, 0x0B, 0x3E,
	0x00, 0x40, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
	0xEA, 0x0C, 0xDF, 0x28, 0x00, 0xE7, 0x04, 0xE3,
	0xFF,
/* GC -> 4th is Function Set and 8th Bit Set 
         6th is Mode Select default Read0 write2*/
	0x00, 0x00, 0x00, 0x00, 0x03, 0x02, 0x05, 0x0F,
	0xFF,
/* AC */
	0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x14, 0x07,
	0x38, 0x39, 0x3A, 0x3B, 0x3C, 0x3D, 0x3E, 0x2D,
	0x01, 0x0F, 0x0F, 0xC0, 0x00
};

void write_registers(unsigned char *regs){
   unsigned i;

   /* write MISCELLANEOUS reg */
   outportb(VGA_MISC_WRITE, *regs);
   regs++;
   /* write SEQUENCER regs */
   for(i = 0; i < VGA_NUM_SEQ_REGS; i++)
   {
      outportb(VGA_SEQ_INDEX, i);
      outportb(VGA_SEQ_DATA, *regs);
      regs++;
   }
    	
   /* unlock CRTC registers */
   outportb(VGA_CRTC_INDEX, 0x03);
   outportb(VGA_CRTC_DATA, inportb(VGA_CRTC_DATA) | 0x80);
   outportb(VGA_CRTC_INDEX, 0x11);
   outportb(VGA_CRTC_DATA, inportb(VGA_CRTC_DATA) & ~0x80);
   /* make sure they remain unlocked */
   regs[0x03] |= 0x80;
   regs[0x11] &= ~0x80;
   /* write CRTC regs */
   for(i = 0; i < VGA_NUM_CRTC_REGS; i++)
   {
      outportb(VGA_CRTC_INDEX, i);
      outportb(VGA_CRTC_DATA, *regs);
      regs++;
   }
   /* write GRAPHICS CONTROLLER regs */
   for(i = 0; i < VGA_NUM_GC_REGS; i++)
   {
      outportb(VGA_GC_INDEX, i);
      outportb(VGA_GC_DATA, *regs);
      regs++;
   }
   /* write ATTRIBUTE CONTROLLER regs */
   for(i = 0; i < VGA_NUM_AC_REGS; i++)
   {
      (void)inportb(VGA_INSTAT_READ);
      outportb(VGA_AC_INDEX, i);
      outportb(VGA_AC_WRITE, *regs);
      regs++;
   }
   
   /* lock 16-color palette and unblank display */
   (void)inportb(VGA_INSTAT_READ);
   outportb(VGA_AC_INDEX, 0x20);

}

/*
 * Clears the VGA screen
 */
void VGA_clear_screen(){
   unsigned int x=0;
   unsigned int y=0;

   for(y=0; y<VGA_height; y++){
      for(x=0; x<VGA_width; x++){
	   // Address 0xA0000 is (0,0)
         VGA_address[(VGA_width/8)*y+(int)(x/8)]=0x00;
      }
   }	
}

void VGA_init(int width, int height, int bpp){
   //setup the vga struct
   VGA_width=(unsigned int)width;
   VGA_height=(unsigned int)height;
   VGA_bpp=bpp; // Bit per pixel 
   VGA_address=0xA0000; 

   write_registers(g_640x480x16);

   //clears the screen
   VGA_clear_screen();
} 

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 tags so that we can more easily read it. Using the tags will preserve code indentation.

Another thing you might want to try is figuring out why you're outputting those values to those ports. It's long and tedious, but it'll help you figure out why it's not working yourself, and change it to get other modes whenever you want.

Code: Select all

 tag next time I post a question on the forum. 

I agree the emulators do not have as good a support for VGA as real hardware, but I tried running the piece of code i've posted on real hardware and it doesnt work and it gives the same output on VirtualBox. strangely the code runs well on Bochs, and the irony is that the real machine that I tried running the code is [b]almost[/b] similar to the configuration of Bochs emulator. 

Not able to figure out which VGA register initialization is causing this. I'll try using the GC->5 default value instead of 02. 

Is their no simpler way of switching to graphics 640X480 mode other than this crude method that I'm trying? Ofcourse, not the interrupt one, because my OS is in protected mode.