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void clrscr();
void putch(char c,unsigned char x,unsigned char y,unsigned char fore,unsigned char back);
void putch(char c,unsigned char x,unsigned char y,unsigned char fore,unsigned char back)
{
    *((unsigned short*)(0xB8000+(x*80+y)))=c|(((back<<4)|(fore&0x0F))<<8);
}
void clrscr()
{
    int i;
    for(i=0;i<80*25;i++)
    {
        *((unsigned short*)0xB8000+i)=(0x20|(((0<<4)|(15&0x0F))<<8));
    }
}

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// High byte is the text attribute (see TEXT_ATTRIBUTE below),
// low byte is the character ASCII code.
static unsigned short * const VIDEO_MEM = (unsigned short *) 0xb8000;

// FIXME: Extend this to a complete list of color codes.
static unsigned short const COLOR_white = 15;
static unsigned short const COLOR_black = 0;

// Use this macro with the COLOR_* constants above to get the
// desired text attribute high byte (high nibble is background, low
// nibble is foreground color). To get the value to write to the
// VIDEO_MEM array, binary-OR this macro with the character
// ASCII code.
#define TEXT_ATTRIBUTE( foreground, background ) ( ( ( ( background ) << 4 ) | ( ( foreground ) & 0x0f ) ) << 8 )

// FIXME: Bad design, as this puts the burden of keeping track
// of "current" cursor position on the caller.
void putch( char const c, unsigned char const pos_x, unsigned char const pos_y, unsigned char const foreground, unsigned char const background )
{
    VIDEO_MEM[ pos_x * 80 + pos_y ] = c | TEXT_ATTRIBUTE( foreground, background );
}

void clear_screen()
{
    for ( int i = 0; i < 80 * 25; ++i )
    {
        VIDEO_MEM[i] = ' ' | TEXT_ATTRIBUTE( COLOR_white, COLOR_black );
    }
}

Code: Select all

*((unsigned short*)0xB8000+i)=(0x20|(((0<<4)|(15&0x0F))<<8));

Code: Select all

int kputc(int c) {
   volatile unsigned char * video = (volatile unsigned char*) (KERNEL_1M + 0xB8000);
   ...
}