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flat assembler > High Level Languages > [C] Better Printc implementation.

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nerdguy



Joined: 24 Nov 2013
Posts: 7
[C] Better Printc implementation.
Hi,
This is my first post on FASM Forums,
Hello to the whole FASM community!
I've been working on a 64 bit Kernel recently,
(github.com/nerdguy12/core64),
I've implemented the putchar functions as follows,

Code:

unsigned int putch(unsigned char string,int y)
{
        char *vgamem = (char *) 0xb8000; // Need a pointer to the VGA Memory
        unsigned int i20;
        i2=(y*80*2);
        vgamem[i2]= string; // Put the string in the VGA Memory
        i2++;
        vgamem[i2]= 0x2F; // And the color
        i2++;
}



The problem starts when I need to print the string at a certain X Position,
I use the line variable to set the Y Position of the text cursor and print the string
there.
I've read the bkerndev and I sum up to this equation.
VGA_MEM = 0xB8000 + (Y*80 + X)
Now if I put the character at this memory location, it would be at (X,Y),
So I change the function to :

Code:

usigned int putch(int X,int Y,char *string)
{
 char *vgamem = (char *) 0xb8000 + (Y*80 + X); // Need a pointer to the VGA Memory
//
// Same code
//
}



I'm doing something wrong here that it doesn't even print to the screen,
What do you think is the problem?
Also a better printc implementation could help.
Post 24 Nov 2013, 10:47
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cod3b453



Joined: 25 Aug 2004
Posts: 616
Welcome Cool

Each character cell is actually two bytes so you need to do:

Code:
char *vgamem = (char *) 0xB8000 + ((Y*80 + X) * 2);
// or
short *vgamem = (short *) 0xB8000 + (Y*80 + X);

The upper 8 bits hold the fore- and back- ground colour codes (4 bits each) while the lower 8 bits are the character code.
Post 24 Nov 2013, 12:59
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