vga print helpers

1 year ago · bd3063a80d
parent 592826e8cd
commit bd3063a80d
2 changed files with 229 additions and 49 deletions
--- a/boot1.s
+++ b/boot1.s
@ -37,17 +37,17 @@ self_load:

  ; Panic if the partition / boot1 starting LBA overflows 16 bits.
  or ebx, ebx
-  jnz panic
+  jnz panic_simple
  ror eax, 16
  or ax, ax
-  jnz panic
+  jnz panic_simple
  ror eax, 16

  ; Calculate the boot1 end LBA and panic if it overflows 16 bits.
  ; n.b. ebx is zero before this so both bx and ebx can be used as the boot1 end LBA.
  mov bx, ax
  add bx, BOOT1_TOTAL_SECTORS
-  jc panic
+  jc panic_simple

  ; Panic if the boot1 end LBA is after the partition end LBA.
  ; If the upper 32 bits of the partition end LBA are nonzero, then it must be greater than our
@ -56,7 +56,7 @@ self_load:
  jnz .end_lba_ok
  ; Compare the boot1 end LBA to the lower 32 bits of the partition end LBA.
  cmp ebx, ecx
-  ja panic
+  ja panic_simple

 .end_lba_ok:

@ -74,7 +74,7 @@ self_load:

  mov ecx, ebx
  call read_sector
-  jc panic
+  jc panic_simple
  
  add ebx, 512
  inc word [bp - 0x02]
@ -82,32 +82,15 @@ self_load:

 .self_load_done:

-  mov ebx, cafebabe
+  ; Check the magic bytes at the end of boot1.
+  push es
+  mov ebx, boot1_magic
  call addr32_to_addr16
-  mov eax, es:[ebx]
-  hlt
-
-  call test_a20
-  add al, 0x30
-  mov byte fs:[0x0000], al
-  hlt
+  cmp dword es:[bx], BOOT1_MAGIC
+  pop es
+  jne panic_simple

-pr_womble:
-  ; Reveal the true nature of jen
-  xor bx, bx
-.loop:
-  cmp bx, WOMBLE_LEN
-  jae .done
-  lea si, [womble + bx]
-  mov dh, [si]
-  mov di, bx
-  shl di, 1
-  mov byte fs:[di], dh
-  mov byte fs:[di + 0x01], 0x1f
-  inc bx
-  jmp .loop
-.done:
-  hlt
+  jmp main


 ; Converts a 32-bit address to a 16-bit sector and offset.
@ -119,8 +102,7 @@ pr_womble:
 ; - cf: unset on success, set on failure
 ; Clobber: none
 addr32_to_addr16:
-  push bp
-  mov bp, sp
+  fnstart
  push es
  push eax

@ -152,9 +134,8 @@ addr32_to_addr16:
 .fail:
  pop eax
  pop es
-  pop bp
  stc
-  ret
+  fnret
  

 ; Reads a single sector at the given LBA into memory.
@ -170,8 +151,7 @@ read_sector:
  ; head       = temp % n_heads
  ; cylinder   = temp / n_heads

-  push bp
-  mov bp, sp
+  fnstart
  push es
  push ebx
  
@ -203,8 +183,14 @@ read_sector:
 .return:
  pop ebx
  pop es
-  pop bp
-  ret
+  fnret
+
+
+panic_simple:
+  mov ax, 0x0003
+  int 0x10
+  mov word fs:[0x0000], 0x4f21
+  hlt


 %if ($ - $$) > 512
@ -212,7 +198,183 @@ read_sector:
 %endif


+main:
+  ; Set VGA mode
+  ; https://mendelson.org/wpdos/videomodes.txt
+  mov ax, 0x0003
+  int 0x10
+
+  ; Disable the cursor (don't want to look at the blink blink blink)
+  mov ax, 0x0100
+  mov cx, 0x3f00
+  int 0x10
+
+  mov word [GLOBALS + VGA_COL], 0x1f00
+
+  call vga_clear
+
+  mov ax, msg_boot1_loaded
+  mov cx, MSG_BOOT1_LOADED_LEN
+  call vga_println
+
+  call test_a20
+  test ax, ax
+  jnz .a20_enabled
+  
+  mov ax, msg_a20_disabled
+  mov cx, MSG_A20_DISABLED_LEN
+  call vga_println
+
+  ; TODO: enable a20
+  hlt
+
+.a20_enabled
+  mov ax, msg_a20_enabled
+  mov cx, MSG_A20_ENABLED_LEN
+  call vga_println
+  
+  hlt
+
+
+; Clear the VGA text buffer.
+; Arguments: none
+; Return: none
+; Clobber: none
+vga_clear:
+  fnstart
+  push di
+  push es
+  push ax
+  push cx
+
+  mov ax, 0xb800
+  mov es, ax
+  mov ax, [GLOBALS + VGA_COL]
+  mov cx, VGA_WIDTH * VGA_HEIGHT
+  xor di, di
+  rep stosw
+  mov word [GLOBALS + TEXTBUF_LINE], 0
+  
+  pop cx
+  pop ax
+  pop es
+  pop di
+  fnret
+
+
+; Scroll the VGA text buffer up one line.
+; Arguments: none
+; Return: none
+; Clobber: none
+vga_scroll:
+  fnstart
+  push si
+  push di
+  push ax
+  push cx
+  push es
+  push ds
+
+  mov ax, 0xb800
+  mov ds, ax
+  mov es, ax
+
+  ; Copy everything up one line.
+  mov cx, VGA_WIDTH * (VGA_HEIGHT - 1)
+  mov si, VGA_WIDTH * 2
+  mov di, 0
+  rep movsw
+
+  ; Clear the last line.
+  mov ax, [GLOBALS + VGA_COL]
+  mov cx, VGA_WIDTH
+  mov di, VGA_WIDTH * (VGA_HEIGHT - 1) * 2
+  rep stosw
+
+  pop ds
+  pop es
+
+  ; Decrement the current textbuf line if it's greater than 0.
+  mov cx, [GLOBALS + TEXTBUF_LINE]
+  xor ax, ax
+  sub cx, 1
+  cmovae ax, cx
+  mov [GLOBALS + TEXTBUF_LINE], ax
+
+  pop cx
+  pop ax
+  pop di
+  pop si
+  fnret
+
+
+; Write one line to the VGA text buffer.
+; Arguments:
+; - ax: pointer to the string to print
+; - cx: string length
+; Return: none
+; Clobber: ax, cx
+vga_println:
+  fnstart
+  push si
+  push di
+  push dx
+  push es
+
+  cmp word [GLOBALS + TEXTBUF_LINE], VGA_HEIGHT
+  jb .scroll_done
+  call vga_scroll
+.scroll_done:
+
+  mov si, ax
+  mov ax, VGA_WIDTH
+  cmp cx, ax
+  cmova cx, ax
+  mov di, VGA_WIDTH * (VGA_HEIGHT - 1) * 2
+
+  xor dx, dx
+  mov ax, [GLOBALS + TEXTBUF_LINE]
+  mov di, VGA_WIDTH * 2
+  mul di
+  mov di, ax
+  
+  mov ax, 0xb800
+  mov es, ax
+  mov ah, [GLOBALS + VGA_COL + 1]
+
+.loop:
+  or cx, cx
+  jz .done
+  mov al, [si]
+  mov es:[di], ax
+  add di, 2
+  inc si
+  dec cx
+  jmp .loop
+  
+.done:
+  inc word [GLOBALS + TEXTBUF_LINE]
+  
+  pop es
+  pop dx
+  pop di
+  pop si
+  fnret
+
+
+enable_a20:
+  fnstart
+  fnret
+
+
+; Check whether the A20 line is enabled. Writes to the boot sector identifier.
+; Arguments: none
+; Return:
+; - ax: 0 if A20 disabled, nonzero if A20 enabled
+; Clobber: none
 test_a20:
+  push bp
+  mov bp, sp
  push gs
  
  ; Restore the boot sector identifier in case it was overwritten by anything.
@ -238,22 +400,20 @@ test_a20:

 .return:
  pop gs
+  pop bp
  ret


-panic:
-  mov ax, 0x0003
-  int 0x10
-  mov word fs:[0x0000], 0x4f21
-  hlt
-
-
-womble     db "jen is a womble!"
-WOMBLE_LEN equ $ - womble
+msg_boot1_loaded     db  "boot1 loaded. hello!"
+MSG_BOOT1_LOADED_LEN equ $ - msg_boot1_loaded
+msg_a20_enabled      db  "a20 enabled"
+MSG_A20_ENABLED_LEN  equ $ - msg_a20_enabled
+msg_a20_disabled     db  "a20 disabled"
+MSG_A20_DISABLED_LEN equ $ - msg_a20_disabled
+msg_panic            db  "fuck"
+MSG_PANIC_LEN        equ $ - msg_panic

-  times 409600 db 0
-cafebabe:
-  dd 0xfeedface
+boot1_magic dd BOOT1_MAGIC

 BOOT1_TOTAL_LEN     equ $ - $$
 BOOT1_TOTAL_SECTORS equ (BOOT1_TOTAL_LEN + 511) / 512
--- a/defines.s
+++ b/defines.s
@ -6,6 +6,11 @@

 %define EBDA_START 0x080000

+%define BOOT1_MAGIC 0x544e4150
+
+%define VGA_WIDTH  80
+%define VGA_HEIGHT 25
+
 ; boot0 base stack frame variable offsets / globals
 ; (we use the same offsets once we copy the variables to the globals section)
 ; -------------------------------------------------------------------------------------------------
@ -29,3 +34,18 @@
 %define GPT_SECTORS_LOADED     0x16
 %define GPT_CURRENT_LBA        0x18
 %define BOOT1_GPT_ENTRY_ADDR   0x1a
+
+; Globals
+; ------------------------------------------------------------------------------------------------
+%define VGA_COL                0x1c
+%define TEXTBUF_LINE           0x1e
+
+%macro fnstart 0
+  push bp
+  mov bp, sp
+%endmacro
+
+%macro fnret 0
+  pop bp
+  ret
+%endmacro