OSDev.org

Posted: **Sun Jan 26, 2020 5:11 pm**

Basically, I have developed to the point where you can print characters to the screen. But I ran into a issue, the text screen has been scrolled down by one. Working in QEMU, but not real hardware. Here is the code I use for printing:

Code: Select all

#include <stdint.h>
#include <stddef.h>
#include "terminal.h"
#include "asm-io.h"
void disable_cursor()
{
	outb(0x3D4, 0x0A);
	outb(0x3D5, 0x20);
}
uint16_t* video_mem;
int row, column;
static const int width = 80;
static const int height = 25;
uint16_t char_entry(unsigned char c, uint8_t color)
{
  return (uint16_t) c | (uint16_t) color << 8;
}
uint8_t char_color(enum color_list fg, enum color_list bg)
{
  return fg | bg << 4;
}
void printc(char c, int color, int x, int y)
{
  video_mem[y * width + x] = char_entry(c, color);
}
void terminal_init(void)
{
  disable_cursor();
  row = 0;
  column = 0;
  video_mem = (uint16_t*)0xB8000;
  for (int y = 0; y < height; y++){
    for (int x = 0; x < width; x++){
      int spot = y * width + x;
      video_mem[spot] = char_entry(' ', char_color(7, 0));
    }
  }
  row = 0;
  column = 0;
  //long string of characters to print, hopefully filling up the screen
  printc('1', char_color(7, 0), column, row++);
  printc('2', char_color(7, 0), column, row++);
  printc('3', char_color(7, 0), column, row++);
  printc('4', char_color(7, 0), column, row++);
  printc('5', char_color(7, 0), column, row++);
  printc('6', char_color(7, 0), column, row++);
  printc('7', char_color(7, 0), column, row++);
  printc('8', char_color(7, 0), column, row++);
  printc('9', char_color(7, 0), column, row++);
  printc('0', char_color(7, 0), column, row++);
  printc('1', char_color(7, 0), column, row++);
  printc('2', char_color(7, 0), column, row++);
  printc('3', char_color(7, 0), column, row++);
  printc('4', char_color(7, 0), column, row++);
  printc('5', char_color(7, 0), column, row++);
  printc('6', char_color(7, 0), column, row++);
  printc('7', char_color(7, 0), column, row++);
  printc('8', char_color(7, 0), column, row++);
  printc('9', char_color(7, 0), column, row++);
  printc('0', char_color(7, 0), column, row++);
  printc('1', char_color(7, 0), column, row++);
  printc('2', char_color(7, 0), column, row++);
  printc('3', char_color(7, 0), column, row++);
  printc('4', char_color(7, 0), column, row++);
  printc('5', char_color(7, 0), column, row++);
}

Is there any obvious flaw I've made?

Posted: **Mon Jan 27, 2020 11:17 am**

djalex234 wrote:But I ran into a issue, the text screen has been scrolled down by one.

I'm not sure I understand what this means. Are you saying there's an empty space at the top of the screen, and the line of text that should be at the bottom of the screen has been cut off? If so, your monitor may not be calibrated correctly. It's very common for LCD monitors to fail automatic calibration when the screen is mostly black.

Posted: **Mon Jan 27, 2020 1:27 pm**

I forgot that this monitor wasn't top quality, the calibration worked. Didn't seem like that was the issue with stuff like Ubuntu working on it perfectly. Thanks for the idea.

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