Added comments to the source code for stage 1

Changed the parameters for the function to load into registers
Changed all the data types to words instead of int in case ints are not allowed

stage1/bootasm2.S

@@ -38,6 +38,8 @@ cons_writeline:
     call    cons_write_crlf
     ret    
 
+# Added Write Hex and Int functions to help with debugging
+
 HexChars:	.ascii "0123456789ABCDEF"
 
 cons_write_hex:
@@ -84,72 +86,78 @@ getdigit:
 IntBuffer:   .string "     "
 
 cons_draw_line:        
-    movw    $0, err
-    movw    x1, %cx
-    movw    y1, %dx
-    sub     x0, %cx
+    movw    $0, err     # Make sure that err starts at 0
+    movw    %ax, (x0)     # Move the initial vars from the registers to static memory
+    movb    %cl, (y0)
+    movw    %bx, (x1)
+    movb    %ch, (y1)
+    movb    %dl, (color)
+
+    movw    x1, %cx     # Load x1 and y1 into the registers
+    movw    y1, %dx     
+    sub     x0, %cx     # Remove x/y0 from x/y1 to get the delta values
     sub     y0, %dx
-    movw    %cx, (deltax)
+    movw    %cx, (deltax)   # Store the delta values
     movw    %dx, (deltay)    
     
 cons_line_check_x:
-    movw    x0, %cx
-    movw    $1, (sx)
-    cmp     x1, %cx
+    movw    x0, %cx     # Load x0 into register cx so we can manipulate this value to plot each pixel
+    movw    $1, (sx)    # Preload x slope with 1
+    cmp     x1, %cx     # Check if x1 is less than x0 and we can move to y
     jl      cons_line_check_y
-    negw    sx
+    negw    sx          # if x1 is greater than we need to flip the slope and the x delta values
     negw    deltax
 
 cons_line_check_y:
-    movw    y0, %dx
-    movw    $1, (sy)
-    cmpw    y1, %dx
+    movw    y0, %dx     # Load y0 into register dx so we can manipulate this value to plot each pixel
+    movw    $1, (sy)    # Preload y slope with 1
+    cmpw    y1, %dx     # Check if y1 is less than y0 and we can start our plotting
     jl      cons_line_prep_loop
-    negw    sy
+    negw    sy          # if y1 is greater than we need to flip the slope y and delta y values
     negw    deltay
 
 cons_line_prep_loop:
-    movw    deltax, %ax
+    movw    deltax, %ax # Calculate the err variable by subtracting delta y from delta x
     sub     deltay, %ax
-    movw    %ax, (err)
+    movw    %ax, (err) 
 
 cons_line_loop_start:
-    xor     %ax, %ax
+    xor     %ax, %ax    # Clear ax and bx for use with the draw function
     xor     %bx, %bx
-    movb    $0x0c, %ah
-    movb    $0, %bh
-    movb    (color), %al
-    int     $0x10
+    movb    $0x0c, %ah  # Set the function byte to plot the pixel
+    movb    $0, %bh     # Set the video page number
+    movb    (color), %al    # Set the color of the pixel
+    int     $0x10       # Call the int
 
-    cmpw    x1, %cx
+    cmpw    x1, %cx     # Check if x0 and x1 are equal, if not then we are still plotting
     jne     cons_line_loop_next_point
-    cmpw    y1, %dx
+    cmpw    y1, %dx     # Check if y0 and y1 are equal, if not then we are still plotting
     jne     cons_line_loop_next_point
-    jmp     cons_line_loop_end          
+    jmp     cons_line_loop_end  # if both x's and y's are equal then we can end the function
 
 cons_line_loop_next_point:
-    movw    err, %ax
-    add     %ax, %ax
+    movw    err, %ax    # Load err into ax so that we can multiply it
+    add     %ax, %ax    # e2 is 2 * err, so we can just add err to itself
 
 cons_line_loop_move_y_point:
     movw    deltay, %bx
-    negw    %bx
-    cmpw    %bx, %ax
+    negw    %bx         # We need negative deltay to compare
+    cmpw    %bx, %ax    # Check if we need to apply the slope value to y
     jle     cons_line_loop_move_x_point
-    negw    %bx
-    subw    %bx, err
-    addw    sx, %cx
+    negw    %bx         # Change deltay back to normal
+    subw    %bx, err    # Remove the deltay from the err check
+    addw    sx, %cx     # Add the slope value to the current y value
     
 cons_line_loop_move_x_point:
     movw    deltax, %bx    
-    cmpw    %bx, %ax
+    cmpw    %bx, %ax    # Check if we need to apply the x slope value
     jge     cons_line_loop_start
-    addw    %bx, err
-    addw    sy, %dx
-    jmp     cons_line_loop_start
+    addw    %bx, err    # Add the deltax to the err value
+    addw    sy, %dx     # Add the slope value to the current x value
+    jmp     cons_line_loop_start    # Go back to the start of the loop
 
 cons_line_loop_end:
-    ret
+    ret     # Finish the loop and return to the call address
 
 real_start:
     movw    $boot_message, %si  # Display our boot message
@@ -162,46 +170,75 @@ draw_start:
     int     $0x10
     xor     %ax, %ax
 
-    movw    $50, x0
-    movw    $50, y0
-    movw    $160, x1
-    movw    $55, y1
-    movb    $12, color
+    movw    $50, %ax    # Plot a line, ax = x0, bx = x1, cl = y0, ch = y1, dl = color
+    movb    $50, %cl    # the X values require a full register but the y's only require a byte since the max value is 200
+    movw    $160, %bx   
+    movb    $55, %ch
+    movb    $12, %dl    # The Color also only requires a byte
     call    cons_draw_line
 
-    movw    $150, x0
-    movw    $150, y0
-    movw    $50, x1
-    movw    $50, y1
-    movb    $10, color
+    # Draw the rest of the lines
+    movw    $160, %ax
+    movb    $55, %cl
+    movw    $90, %bx
+    movb    $150, %ch
+    movb    $11, %dl
     call    cons_draw_line
 
-    movw    $150, x0
-    movw    $150, y0
-    movw    $160, x1
-    movw    $55, y1
-    movb    $11, color
+    movw    $90, %ax
+    movb    $150, %cl
+    movw    $50, %bx
+    movb    $50, %ch
+    movb    $14, %dl
     call    cons_draw_line
 
-    movw    $10, x0
-    movw    $10, y0
-    movw    $310, x1
-    movw    $190, y1
-    movb    $9, color
+    movw    $10, %ax
+    movb    $10, %cl
+    movw    $310, %bx
+    movb    $10, %ch
+    movb    $9, %dl
     call    cons_draw_line
 
-    movw    $310, x0
-    movw    $190, y0
-    movw    $10, x1
-    movw    $95, y1
-    movb    $8, color
+    movw    $310, %ax
+    movb    $10, %cl
+    movw    $310, %bx
+    movb    $190, %ch
+    movb    $10, %dl
     call    cons_draw_line
 
-    movw    $10, x0
-    movw    $95, y0
-    movw    $10, x1
-    movw    $10, y1
-    movb    $7, color
+    movw    $310, %ax
+    movb    $190, %cl
+    movw    $10, %bx
+    movb    $190, %ch
+    movb    $13, %dl
+    call    cons_draw_line
+
+    movw    $10, %ax
+    movb    $190, %cl
+    movw    $10, %bx
+    movb    $10, %ch
+    movb    $15, %dl
+    call    cons_draw_line
+
+    movw    $75, %ax
+    movb    $150, %cl
+    movw    $250, %bx
+    movb    $110, %ch
+    movb    $1, %dl
+    call    cons_draw_line
+
+    movw    $210, %ax
+    movb    $30, %cl
+    movw    $300, %bx
+    movb    $150, %ch
+    movb    $6, %dl
+    call    cons_draw_line
+
+    movw    $180, %ax
+    movb    $180, %cl
+    movw    $170, %bx
+    movb    $20, %ch
+    movb    $3, %dl
     call    cons_draw_line
 
 endless_loop:                   # Loop forever more
@@ -211,14 +248,14 @@ endless_loop:                   # Loop forever more
 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
+x0:     .word    0
+y0:     .word    0
+x1:     .word    0
+y1:     .word    0
+deltax:     .word    0
+deltay:     .word    0
+sx:     .word    0
+sy:     .word    0
+err:    .word    0
+e2:     .word    0
 color:  .byte   0