Stage0/x86/stage0/stage0_monitor.hex

## Copyright (C) 2016 Jeremiah Orians
## This file is part of stage0.
##
## stage0 is free software: you can redistribute it and/or modify
## it under the terms of the GNU General Public License as published by
## the Free Software Foundation, either version 3 of the License, or
## (at your option) any later version.
##
## stage0 is distributed in the hope that it will be useful,
## but WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
## GNU General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with stage0.  If not, see <http://www.gnu.org/licenses/>.

# start:
# Let us first setup our stack
BC0001            # mov sp,0x100
B8007E            # mov ax,0x7e00
8ED0              # mov ss,ax
# Setup segment to shove input
B80010            # mov ax,0x1000
8EC0              # mov es,ax
BD0000            # mov bp,0x0
# Initialize variables
B80000            # mov ax,0x0
BF0100            # mov di,0x1
BE0000            # mov si,0x0

# loop:
E85100            # call read_char
# Check for C-d
3C04              # cmp al,0x4
7505              # jnz 0x25 [Skip over next 2 instructions]
E8E400            # call execute_code
EBF4              # jmp loop
# Check for C-l
3C0C              # cmp al,0xc
7505              # jnz 0x2e [Skip over next 2 instructions]
E84600            # call clear_screen
EBEB              # jmp loop
# Check for [Enter]
3C0D              # cmp al,0xd
7505              # jnz 0x37 [Skip over next 2 instructions]
E85800            # call display_newline
EBE2              # jmp loop

# Otherwise just print the char
E82E00            # call print_char
E88D00            # call hex
3C00              # cmp al,0x0 [Check if is hex char]
7CD8              # jl loop
83FF00            # cmp di,byte +0x0 [Check if toggled]
740A              # jz 0x50 [Skip over next 4 instructions]

# Process first nibble of pair
BE0F00            # mov si,0xf
21C6              # and si,ax
BF0000            # mov di,0x0
EBC9              # jmp loop

# Process second nibble of pair
C1E604            # shl si,byte 0x4
83E00F            # and ax,byte +0xf
01F0              # add ax,si
BF0100            # mov di,0x1
89EB              # mov bx,bp

# Write out byte
268807            # mov [es:bx],al

# Update our pointer
83C501            # add bp,byte +0x1
E8C900            # call insert_spacer
EBB1              # jmp loop

# print_char:
B40E              # mov ah,0xe
CD10              # int 0x10
C3                # ret

# read_char:
B400              # mov ah,0x0
CD16              # int 0x16
C3                # ret

# clear_screen:
# The actual clearing of the screen
B000              # mov al,0x0
B406              # mov ah,0x6
B707              # mov bh,0x7
B100              # mov cl,0x0
B500              # mov ch,0x0
B250              # mov dl,0x50
B618              # mov dh,0x18
CD10              # int 0x10
# The resetting of the cursor
B402              # mov ah,0x2
B700              # mov bh,0x0
B600              # mov dh,0x0
B200              # mov dl,0x0
CD10              # int 0x10
C3                # ret

# display_newline:
E81B00            # call get_cursor_position
80FC0C            # cmp ah,0xc
7E04              # jng 0x99 [Skip over next 2 instructions]
E81C00            # call word 0xb4
C3                # ret
# Move the cursor down if required
B601              # mov dh,0x1
00E6              # add dh,ah
B402              # mov ah,0x2
B700              # mov bh,0x0
B200              # mov dl,0x0
CD10              # int 0x10
B00D              # mov al,0xd
E8BEFF            # call print_char
C3                # ret

# get_cursor_position:
B403              # mov ah,0x3
B700              # mov bh,0x0
CD10              # int 0x10
89D0              # mov ax,dx
C3                # ret

# scroll_window:
B001              # mov al,0x1
B406              # mov ah,0x6
B707              # mov bh,0x7
B100              # mov cl,0x0
B500              # mov ch,0x0
B250              # mov dl,0x50
B618              # mov dh,0x18
CD10              # int 0x10
B00D              # mov al,0xd
E89FFF            # call print_char
C3                # ret

# hex:
# Deal with line comments starting with #
3C23              # cmp al,0x23
742A              # jz ascii_comment
# Deal with line comments starting with ;
3C3B              # cmp al,0x3b
7426              # jz ascii_comment
# Deal with all ascii less than '0'
3C30              # cmp al,0x30
7C1F              # jl ascii_other
# Deal with '0' through '9'
3C3A              # cmp al,0x3a
7C12              # jl ascii_num
# Deal with all ascii less than 'A'
3C41              # cmp al,0x41
7C17              # jl ascii_other
# Deal with 'A' through 'F'
3C47              # cmp al,0x47
7C10              # jl ascii_high
# Deal with all ascii less than 'a'
3C61              # cmp al,0x61
7C0F              # jl ascii_other
# Deal with 'a' through 'f'
3C67              # cmp al,0x67
7C05              # jl ascii_low
# Deal with everything else
EB09              # jmp ascii_other

# ascii_num:
2C30              # sub al,0x30
C3                # ret

# ascii_low:
2C57              # sub al,0x57
C3                # ret

# ascii_high:
2C37              # sub al,0x37
C3                # ret

# ascii_other:
B0FF              # mov al,0xff
C3                # ret

# ascii_comment:
E872FF            # call read_char
E86AFF            # call print_char
3C0D              # cmp al,0xd
75F6              # jnz ascii_comment
E8AFFF            # call scroll_window
EBEE              # jmp ascii_other

# execute_code:
# Clear the screen to be nice
E868FF            # call clear_screen

# Zero all registers and segments before jump
B80000            # mov ax,0x0
BB0000            # mov bx,0x0
B90000            # mov cx,0x0
BA0000            # mov dx,0x0
BE0000            # mov si,0x0
BF0000            # mov di,0x0
BD0000            # mov bp,0x0
8ED8              # mov ds,ax
8ED0              # mov ss,ax
8EC0              # mov es,ax
8EE0              # mov fs,ax
8EE8              # mov gs,ax

# Load the code that we input by hand
680010            # push word 0x1000
6A00              # push byte +0x0
# Using intersegment return
CF                # iretw

# insert_spacer:
B020              # mov al,0x20
E834FF            # call word 0x68
C3                # ret

# done:
F4                # hlt
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
90 90 90 90       # 4 nops
55AA              # Magic Number