hazel/kernel/vga.c

/**
 * @file vga.c
 * @brief Basic functions for interacting with the CRTC controller in VGA text-mode.
 * @author rami
 * @version 0.1
 * @date 2024-02-03
 */

#include <kernel/vga.h>
#include <kernel/io.h>
#include <kernel/log.h>
#include <kernel/mem.h>

enum VGA_COLOR vga_color = VGA_COLOR_WHITE;

uint16_t get_cursor_pos() {
    uint16_t pos = 0;

    /* Tell CRTC controller we want the low cursor position */
    outb(CRTC_ADDR_PORT, CRTC_CURSOR_LO_REGISTER);
    /* Read it through the data port */
    pos = inb(CRTC_DATA_PORT);
    
    /* Repeat with high position */
    outb(CRTC_ADDR_PORT, CRTC_CURSOR_HI_REGISTER);
    uint16_t hi_pos = 0;
    hi_pos = inb(CRTC_DATA_PORT);
    pos |= hi_pos << 8;

    return pos;
}

void set_cursor_pos(uint16_t pos) {
    /* Tell CRTC controller we want the low cursor position */
    outb(CRTC_ADDR_PORT, CRTC_CURSOR_LO_REGISTER);
    outb(CRTC_DATA_PORT, (uint8_t)(pos & 0xFF));
    /* Repeat with high position */
    outb(CRTC_ADDR_PORT, CRTC_CURSOR_HI_REGISTER);
    outb(CRTC_DATA_PORT, (uint8_t)((pos >> 8) & 0xFF));
}

void clear_screen(void) {
    char *video_memory = (char *)VGA_MEMORY_ADDR;
    for (int i = 0; i < VGA_MAX_COLS * VGA_MAX_ROWS; i++) {
       video_memory[i * 2] = 0;
    }

    set_cursor_pos(0);
}

void vga_putc(char character) {
    uint16_t pos = get_cursor_pos();

    if (pos == VGA_MAX_COLS * VGA_MAX_ROWS) {
        if (character != '\n') {
            // Move video memory up one row
            memcpy((char*)VGA_MEMORY_ADDR, (char *)(VGA_MEMORY_ADDR + VGA_MAX_COLS*2), VGA_MAX_COLS * (VGA_MAX_ROWS - 1) * 2);
            // Clear last row
            for (int i = 0; i < VGA_MAX_COLS*2; i+=2) {
                ((char *)(VGA_MEMORY_ADDR + VGA_MAX_COLS*(VGA_MAX_ROWS - 1)*2))[i] = 0;
                ((char *)(VGA_MEMORY_ADDR + VGA_MAX_COLS*(VGA_MAX_ROWS - 1)*2))[i+1] = 0x0f;
            }
            pos = VGA_MAX_COLS * (VGA_MAX_ROWS - 1);
        } else {
            // Move video memory up two rows
            memcpy((char*)VGA_MEMORY_ADDR, (char *)(VGA_MEMORY_ADDR + VGA_MAX_COLS*2*2), VGA_MAX_COLS * (VGA_MAX_ROWS - 2) * 2);
            // Clear last 2 rows
            for (int i = 0; i < VGA_MAX_COLS*2*2; i+=2) {
                ((char *)(VGA_MEMORY_ADDR + VGA_MAX_COLS*(VGA_MAX_ROWS - 2)*2))[i] = 0;
                ((char *)(VGA_MEMORY_ADDR + VGA_MAX_COLS*(VGA_MAX_ROWS - 2)*2))[i+1] = 0x0f;
            }
            pos = VGA_MAX_COLS * (VGA_MAX_ROWS - 2);
        }
    }

    char *video_memory = (char *)VGA_MEMORY_ADDR + pos * 2;

    if (character == '\n') {
        uint16_t next_line = VGA_MAX_COLS * (pos / VGA_MAX_COLS + 1);
        set_cursor_pos(next_line);
    } else {
        video_memory[0] = character;
        video_memory[1] = vga_color;
        set_cursor_pos(pos + 1);
    }
}

void popchar() {
    uint16_t pos = get_cursor_pos();
    if (pos == 0) return;
    char *video_memory = (char *)(VGA_MEMORY_ADDR + (pos - 1) * 2);
    video_memory[0] = 0;
    set_cursor_pos(pos - 1);
}

void set_color(enum VGA_COLOR col) {
    vga_color = col;
}