Make a fancy border and background style and clean up spacing when pr…

…inting

Now print 16 bytes per row with an extra space between every 8.
Also handle scrolling and new lines in the new section that's printable

bootstrap.asm

@@ -8,6 +8,11 @@
 ; See Figure 4-3 of the 1987 BIOS manual. (page 195)
 %define EOT 0x2004 ; Ctrl+D
 
+%define MAIN_COLOR 0x17
+%define BORDER_COLOR 0x91
+%define MAIN_TOP_LEFT 0x0110 ; row = 1,  col = 16
+%define MAIN_BOTTOM_RIGHT 0x173F ; row = 23, col = 79-16
+
 ; Set video mode, 16 color 80x25 chars
 ;
 ; The IBM BIOS manual describes a long procedure for determining which video
@@ -31,23 +36,49 @@ int 0x10
 
 ; Color byte is: bg-intensity,bg-r,bg-g,bg-b ; fg-intensity,fg-r,fg-g,fg-b
 
+; Set cursor shape to an underline
+mov ax, 0x0100
+mov cx, 0x0607
+int 0x10
+
+; Set the border color (by clearing the whole screen)
+mov ax, 0x0600
+xor cx, cx     ; row = 0,  col = 0
+mov dx, 0x184F ; row = 24, col = 79
+mov bh, BORDER_COLOR
+int 0x10
+
+; Set the background color (by clearing just the middle)
+mov ax, 0x0600
+mov cx, MAIN_TOP_LEFT
+mov dx, MAIN_BOTTOM_RIGHT
+mov bh, MAIN_COLOR
+int 0x10
+
 ; Print the starting greeting
 mov ax, 0x1301 ; Write String, move cursor mode in al
 mov bp, greeting ; String pointer in es:bp (es is at code start from bootsect-header.asm)
 mov cx, greeting_len ; Streng length
-xor dx, dx ; Zero cursor position
-mov bx, 0x0080 ; Zero page number, and colors (grey backgound, black text)
+mov dx, 0x0010 ; row = 0, col = 16
+mov bx, BORDER_COLOR ; bh = 0 (page number); bl = color
+int 0x10
+
+; Set cursor position to the start
+mov ax, 0x0200
+mov dx, 0x0110 ; row = 0, col = 16
+xor bh, bh ; page 0
 int 0x10
 
 ; --- Global register variables ---
 ;
+; dx      - cursor position (set above)
 ; [es:di] - the code the user types
 ; cl      - storage for one byte while the user types it out (2 chars per byte)
 ; ch      - non-zero iff the first nibble is written (the nibble could be zero)
 mov ax, USER_CODE_LOC
 mov es, ax
-xor cx, cx
 xor di, di
+xor cx, cx
 
 ; Note: all of the jumps loop back here except for run_code
 typing_loop:
@@ -93,13 +124,16 @@ save_and_print_nibble:
     test ch, ch ; Check the sentinel value in ch
     jnz save_and_print_second_nibble
 
+; save_and_print_first_nibble:
     shl cl, 4 ; Shift the first nibble to the high half
     mov ch, 0xFF ; Signal that we have seen the first nibble
 
     ; Print the first nibble (in al)
     mov ah, 0x0E ; Write teletype character
-    mov bx, 0x000F ; Page number and color
+    xor bx, bx
     int 0x10
+    inc dl ; Update the cursor location
+    ; Note: the first nibble never causes a new line
 
     jmp typing_loop
 
@@ -112,15 +146,48 @@ save_and_print_second_nibble:
 
     ; Print the second nibble (in al)
     mov ah, 0x0E ; Write teletype character
-    mov bx, 0x000F ; Page number and color
+    xor bx, bx
     int 0x10
 
-    ; Print a space between each byte
-    mov al, ' '
-    mov ah, 0x0E ; Write teletype character
-    mov bx, 0x000F ; Page number and color
+    cmp dl, 0x26 ; The column of the last char of the 8th byte
+    je extra_space
+
+    cmp dl, 0x3F ; The last column of the row
+    je new_line
+
+    ; Normal case, the char printed plus 1 space
+    add dl, 2
+    jmp set_cursor
+
+extra_space: ; Put two spaces in the middle
+    add dl, 3
+    jmp set_cursor
+
+new_line:
+    inc dh ; Next row
+    mov dl, 0x10 ; Beginning column
+
+    cmp dh, 24 ; if we're at the bottom
+    jne set_cursor
+    ; if we're at the bottom scroll
+    push cx
+    push dx
+
+    mov ax, 0x0601 ; scroll up one line
+    mov cx, MAIN_TOP_LEFT
+    mov dx, MAIN_BOTTOM_RIGHT
+    mov bh, MAIN_COLOR
     int 0x10
 
+    pop dx
+    pop cx
+
+    dec dh ; Back up one since we scrolled
+set_cursor:
+    mov ah, 0x02
+    xor bh, bh
+    int 0x10 ; dx is the cursor position
+
     jmp typing_loop
 
 run_code: