CODEWITHSUNDEEP
cassemblyx86osdevvga
Narasimha Prasanna HN
Narasimha Prasanna HN

Reputation: 662

VGA Display problem in my custom OS kernel

I am developing an Operating System as a hobby project. I interfaced VGA display by using address 0xB8000, and number of rows are set to 25, and columns are set to 80. I have used following clear screen function : 

void vga_init(void) {

    // Initialise the VGA variables and clear the screen : :
    vga_buffer_pointer = (uint16_t *)  VGA_MEMORY_LOCATION;

    //start clear using 2 pass loop : 
    uint8_t iter_i = 0;
    uint8_t iter_j = 0;

    for(iter_i = 0; iter_i < VGA_ROWS; iter_i ++) {

        for(iter_j = 0; iter_j < VGA_COLS; iter_j++) {
            uint8_t index  = (VGA_COLS *  iter_i) + iter_j;

            vga_buffer_pointer[index] = ((uint16_t)color << 8) | ' ';
        }
    }

    enable_cursor(14,15);
}

I am initialising the screen with green color. The display occupies only a porting of the qemu terminal screen, As shown below :

a busy cat

But I want, the entire terminal to be green. And the display should use the entire terminal. Any help is most appreciated. Thank you

I have attached a gist of my code.

VGA.c

Upvotes: 1

Views: 463

Answers (1)

Michael Petch
Michael Petch

Reputation: 47573

Change:

uint8_t index = (VGA_COLS * iter_i) + iter_j;

to:

uint16_t index = (VGA_COLS * iter_i) + iter_j;

A uint8_t isn't big enough to hold the calculation for the index so it is being truncated causing only part of the display to be erased.

Upvotes: 4

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