1 files changed, 114 insertions, 5 deletions
diff --git a/src/boot.asm b/src/boot.asm
index 08b2834..c19534e 100644
--- a/src/boot.asm
+++ b/src/boot.asm
@@ -8,6 +8,11 @@ support_flags equ 0x4000
 pci_hw_char   equ 0x4001
 pci_ver       equ 0x4002
 last_pci_bus  equ 0x4004
+bios_mmap_len equ 0x4006
+vbe_mode      equ 0x4008
+
+vbe_block     equ 0x4200
+vbe_mode_info equ 0x4400
 
 pci_support equ 0x80
 pae_support equ 0x40
@@ -18,10 +23,7 @@ pae_support equ 0x40
 
   xor ax, ax
   mov ss, ax
-  mov sp, 0x7ffc
-
-  mov ax, 0x0013
-  int 0x10
+  mov sp, 0x8000
 
   mov ax, kernel_segment
   mov es, ax
@@ -72,7 +74,95 @@ mmap_loop:
   test ebx, ebx
   jnz mmap_loop
 mmap_end:
-  mov word [0x4006], di
+  mov word [bios_mmap_len], di
+
+  xor ax, ax
+  mov es, ax
+  mov di, vbe_block
+  mov ah, 0x4f
+
+  mov dword [di], 0x32454256;'VBE2'
+
+  int 0x10
+
+  cmp dword [di], 0x41534556;'VESA'
+  jne no_vbe
+
+  mov bx, word [di + 0x0e]
+  mov ax, word [di + 0x10]
+  mov fs, ax
+  xor esi, esi
+  mov bp, 0xffff
+  mov di, 0x5000
+
+vbe_loop:
+  max_height equ 800
+  ;fs:bx is mode pointer
+  ;esi is highest resolution yet (width * height)
+  ;bp is that mode's number
+  ;uses 0x5000 - 0x50ff as mode info buffer
+  ;skips those without byte-aligned pixels
+
+  mov cx, word [fs:bx]
+  cmp cx, 0xffff
+  je got_highest_vbe
+
+  add bx, 4
+
+  mov ax, 0x4f01
+  int 0x10
+
+  mov al, byte [di]
+
+  test al, 0x01
+  jz vbe_loop
+
+  test al, 0x10
+  jz vbe_loop
+
+  test al, 0x80
+  jz vbe_loop
+
+  mov dx, word [di + 0x14];height
+  cmp dx, max_height
+  jg vbe_loop
+
+  mov ax, word [di + 0x12];width
+  mul dx
+
+  shl edx, 16
+  mov dx, ax
+
+  xor eax, eax
+
+  mov al, byte [di + 0x19];bpp
+  test al, 0x07
+  jnz vbe_loop
+
+  mul edx
+
+  cmp eax, esi
+  jle vbe_loop
+
+  mov esi, eax
+  mov bp, cx
+  jmp vbe_loop
+
+got_highest_vbe:
+  cmp bp, 0xffff
+  je no_vbe
+
+  mov cx, bp
+  mov ax, 0x4f01
+  mov di, vbe_mode_info
+  int 0x10
+
+  or ch, 0x40
+  mov word [vbe_mode], cx
+
+  mov ax, 0x4f02
+  mov bx, cx
+  int 0x10
 
   cli
 
@@ -84,6 +174,25 @@ mmap_end:
 
   jmp 0x10:pmode
 
+no_vbe:
+  xor ax, ax
+  mov es, ax
+
+  mov ax, 0x1300
+  mov bx, 0x004f
+  mov cx, no_vbe_str.len
+  xor dx, dx
+  mov bp, no_vbe_str
+  int 0x10
+
+real_halt:
+  hlt
+  jmp real_halt
+
+no_vbe_str:
+  db "NO VBE2!"
+.len equ $ - no_vbe_str
+
 bits 32
 
 pmode: