Initial Commit

stage1/bootasm2.S

@@ -0,0 +1,224 @@
+# Second stage of the boot loader
+
+.code16                         # Assemble for 16-bit mode
+.globl start
+start:
+    jmp     real_start
+
+# Write to the console using BIOS.
+# 
+# Input: SI contains the address of the null-terminated string to be displayed
+
+cons_write:
+    movb    $0x0e, %ah           # 0x0e is the INT 10h BIOS call to output the value contained in AL to screen
+
+cons_write_rpt:
+    movb    (%si), %al          # Load the byte at the location contained in the SI register into AL   
+    inc     %si                 # Add 1 to the value in SI
+    cmp     $0, %al             # Compare the value in AL with 0
+    jz      cons_write_done     # If it is zero, then we are done
+    int     $0x10               # Output the character in AL to the screen
+    jmp     cons_write_rpt      # and continue
+
+cons_write_done:                # Something that is called will never return 
+    ret                         # until a 'ret' instruction is encountered.  Labels do 
+                                # not give a program any structure.  They just give a 
+                                # memory location a name that we can use in our code. 
+
+cons_write_crlf:
+    movb    $0x0e, %ah          # Output CR
+    movb    $0x0d, %al
+    int     $0x10
+    movb    $0x0a, %al          # Output LF
+    int     $0x10
+    ret
+
+cons_writeline:
+    call    cons_write
+    call    cons_write_crlf
+    ret    
+
+HexChars:	.ascii "0123456789ABCDEF"
+
+cons_write_hex:
+	movw	$4, %cx
+    movb    $0x0E, %ah
+	
+hexloop:
+    rol     $4, %bx
+    movw    %bx, %si
+    and     $0x000F, %si
+    movb    HexChars(%si), %al
+	int		$0x10
+	loop	hexloop
+	ret
+
+cons_write_int:
+    movw    $IntBuffer + 4, %si
+    movw    %bx, %ax
+
+    cmpw    $0, %ax
+    jge     getdigit
+
+    xor     %ax, %ax
+    movb    $0x0E, %ah
+    movb    $0x2D, %al
+	int		$0x10
+
+    movw    %bx, %ax
+    negw    %ax
+	
+getdigit:
+	xor		%dx, %dx
+	movw	$10, %cx
+	idiv	%cx
+	addb	$48, %dl
+	movb	%dl, (%si)
+	dec		%si
+	cmp		$0, %ax
+	jne		getdigit
+	inc		%si
+	call	cons_write
+	ret
+	
+IntBuffer:   .string "     "
+
+cons_draw_line:        
+    movw    $0, err
+    movw    x1, %cx
+    movw    y1, %dx
+    sub     x0, %cx
+    sub     y0, %dx
+    movw    %cx, (deltax)
+    movw    %dx, (deltay)    
+    
+cons_line_check_x:
+    movw    x0, %cx
+    movw    $1, (sx)
+    cmp     x1, %cx
+    jl      cons_line_check_y
+    negw    sx
+    negw    deltax
+
+cons_line_check_y:
+    movw    y0, %dx
+    movw    $1, (sy)
+    cmpw    y1, %dx
+    jl      cons_line_prep_loop
+    negw    sy
+    negw    deltay
+
+cons_line_prep_loop:
+    movw    deltax, %ax
+    sub     deltay, %ax
+    movw    %ax, (err)
+
+cons_line_loop_start:
+    xor     %ax, %ax
+    xor     %bx, %bx
+    movb    $0x0c, %ah
+    movb    $0, %bh
+    movb    (color), %al
+    int     $0x10
+
+    cmpw    x1, %cx
+    jne     cons_line_loop_next_point
+    cmpw    y1, %dx
+    jne     cons_line_loop_next_point
+    jmp     cons_line_loop_end          
+
+cons_line_loop_next_point:
+    movw    err, %ax
+    add     %ax, %ax
+
+cons_line_loop_move_y_point:
+    movw    deltay, %bx
+    negw    %bx
+    cmpw    %bx, %ax
+    jle     cons_line_loop_move_x_point
+    negw    %bx
+    subw    %bx, err
+    addw    sx, %cx
+    
+cons_line_loop_move_x_point:
+    movw    deltax, %bx    
+    cmpw    %bx, %ax
+    jge     cons_line_loop_start
+    addw    %bx, err
+    addw    sy, %dx
+    jmp     cons_line_loop_start
+
+cons_line_loop_end:
+    ret
+
+real_start:
+    movw    $boot_message, %si  # Display our boot message
+    call    cons_writeline
+
+draw_start:
+    # Set the Video mode to VGA 320 x 200 x 8    
+    movb    $0, %ah
+    movb    $0x13, %al
+    int     $0x10
+    xor     %ax, %ax
+
+    movw    $50, x0
+    movw    $50, y0
+    movw    $160, x1
+    movw    $55, y1
+    movb    $12, color
+    call    cons_draw_line
+
+    movw    $150, x0
+    movw    $150, y0
+    movw    $50, x1
+    movw    $50, y1
+    movb    $10, color
+    call    cons_draw_line
+
+    movw    $150, x0
+    movw    $150, y0
+    movw    $160, x1
+    movw    $55, y1
+    movb    $11, color
+    call    cons_draw_line
+
+    movw    $10, x0
+    movw    $10, y0
+    movw    $310, x1
+    movw    $190, y1
+    movb    $9, color
+    call    cons_draw_line
+
+    movw    $310, x0
+    movw    $190, y0
+    movw    $10, x1
+    movw    $95, y1
+    movb    $8, color
+    call    cons_draw_line
+
+    movw    $10, x0
+    movw    $95, y0
+    movw    $10, x1
+    movw    $10, y1
+    movb    $7, color
+    call    cons_draw_line
+
+endless_loop:                   # Loop forever more
+    jmp     endless_loop    
+
+# Program data
+boot_message:     
+    .string "Boot Loader Stage 2 loaded"             
+
+x0:     .int    0
+y0:     .int    0
+x1:     .int    0
+y1:     .int    0
+deltax:     .int    0
+deltay:     .int    0
+sx:     .int    0
+sy:     .int    0
+err:    .int    0
+e2:     .int    0
+color:  .byte   0