I'm working on a little operating system, and I've decided that I've grown tired of VGA's 320x200 8-bit color limitations. I really don't want to refactor all my code, so my goal is implementing the simplest way to get 720p and 16-bit colors. Here's some of my code (and a link to my GitHub):
boot.asm:
[org 0x7c00]
KERNEL_LOCATION equ 0x1000
mov [BOOT_DISK], dl
xor ax, ax
mov es, ax
mov ds, ax
mov bp, 0x8000
mov sp, bp
mov bx, KERNEL_LOCATION
mov dh, 32
mov ah, 0x02
mov al, dh
mov ch, 0x00
mov dh, 0x00
mov cl, 0x02
mov dl, [BOOT_DISK]
int 0x13
mov ah, 0x00
mov al, 0x13
int 0x10 ; text mode
CODE_SEG equ GDT_code - GDT_start
DATA_SEG equ GDT_data - GDT_start
cli
lgdt [GDT_descriptor]
mov eax, cr0
or eax, 1
mov cr0, eax
jmp CODE_SEG:start_protected_mode
jmp $
BOOT_DISK: db 0
GDT_start:
GDT_null:
dd 0x0
dd 0x0
GDT_code:
dw 0xffff
dw 0x0
db 0x0
db 0b10011010
db 0b11001111
db 0x0
GDT_data:
dw 0xffff
dw 0x0
db 0x0
db 0b10010010
db 0b11001111
db 0x0
GDT_end:
GDT_descriptor:
dw GDT_end - GDT_start - 1
dd GDT_start
[bits 32]
start_protected_mode:
mov ax, DATA_SEG
mov ds, ax
mov ss, ax
mov es, ax
mov fs, ax
mov gs, ax
mov ebp, 0x90000 ; 32 bit stack base pointer
mov esp, ebp
jmp KERNEL_LOCATION
times 510-($-$$) db 0
dw 0xaa55
kernel.cpp:
typedef unsigned char uint8_t;
typedef unsigned char u8;
typedef unsigned short uint16_t;
typedef unsigned int u32;
typedef u32 size_t;
#define SCREEN_WIDTH 320
#define SCREEN_HEIGHT 200
#define SCREEN_SIZE (SCREEN_WIDTH * SCREEN_HEIGHT)
#define FPS 30
#define PIT_HERTZ 1193131.666
#define CLOCK_HIT (int)(PIT_HERTZ/FPS)
#define KEY_LEFT 0x4B
#define KEY_UP 0x48
#define KEY_RIGHT 0x4D
#define KEY_DOWN 0x50
static uint8_t *BUFFER = (uint8_t *) 0xA0000;
// double buffers
uint8_t _sbuffers[2][SCREEN_SIZE];
uint8_t _sback = 0;
#define CURRENT (_sbuffers[_sback])
#define SWAP() (_sback = 1 - _sback)
#define screen_buffer() (_sbuffers[_sback])
#define screen_set(_p, _x, _y)\
(_sbuffers[_sback][((_y) * SCREEN_WIDTH + (_x))]=(_p))
static inline void outb(uint16_t port, uint8_t val)
{
asm volatile ( "outb %0, %1" : : "a"(val), "Nd"(port) );
}
static inline uint8_t inb(uint16_t port)
{
uint8_t ret;
asm volatile ( "inb %1, %0"
: "=a"(ret)
: "Nd"(port) );
return ret;
}
const unsigned char font[128-32][8] = {
{ 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00}, // U+0020 (space)
/*deleted to aid in shorter code...*/
{ 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00} // U+007F
};
static inline void *memcpy(void *dst, const void *src, size_t n)
{
u8 *d = (u8*)dst;
const u8 *s = (const u8*)src;
while (n-- > 0) {
*d++ = *s++;
}
return d;
}
void screen_swap() {
memcpy(BUFFER, CURRENT, SCREEN_SIZE);
SWAP();
}
unsigned read_pit(void) {
unsigned count = 0;
// al = channel in bits 6 and 7, remaining bits clear
outb(0x43,0b0000000);
count = inb(0x40); // Low byte
count |= inb(0x40)<<8; // High byte
return count;
}
void draw_char(char c, int x, int y, unsigned char color)
{
const unsigned char *glyph = font[(int)c-32];
for(int cy=0;cy<8;cy++){
for(int cx=0;cx<8;cx++){
if(((int)glyph[cy]&(1<<cx))==(1<<cx)){
screen_set(color,x+cx,y+cy);
}
}
}
}
void draw_string(const char * s, int x, int y, unsigned char color) {
int i = 0;
while(s[i] != false) {
draw_char(s[i],x+(i*8),y,color);
i++;
}
}
void draw_rect(int pos_x, int pos_y, int w, int h, unsigned char color) {
for(int y = 0; y<h; y++) {
for(int x = 0; x<w; x++) {
screen_set(color,x+pos_x,y+pos_y);
}
}
}
Since you're targetting 16-bit color, suggesting to use the higher VGA 640x480 resolution isn't going to cut it for you!
What you need is switching to a VESA video mode. The "VESA BIOS EXTENSION (VBE) Core Function Standard v3" from https://vesa.org/ is the document that you should read.
Unrelated to your graphics question, but nonetheless important are the errors in your bootloader code. And because I see that you keep re-posting these errors, I find it is urgent that you address these...
mov [BOOT_DISK], dl instruction already depends on a correct DS segment register. You must store DL after setting up the segment registers.xor ax, ax
mov ds, ax
mov es, ax
mov ss, ax ; \
mov sp, 0x8000 ; /
mov [BOOT_DISK], dl
and
mov ax, DATA_SEG
mov ds, ax
mov es, ax
mov fs, ax
mov gs, ax
mov ss, ax ; \
mov esp, 0x00090000 ; / 32 bit stack base pointer
mov ebp, esp ; Only if you need this!
You cannot omit checking the error status after the BIOS.LoadSectors function 02h! Should an error occur, retry the operation a few times, then fail with a suitable message.
Comment your code, and write comments that are true! With mov ah, 0x00 mov al, 0x13 int 0x10 ; text mode, you are setting up a graphics mode.