add documentation and minor refactoring
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Tibo
parent
3ca4ce76f0
commit
0a66a89beb
1 changed files with 136 additions and 92 deletions
228
messages.asm
228
messages.asm
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@ -1,11 +1,12 @@
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org 0x7C00 ; The boot code on a drive always gets loaded at address 0x7C00
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bits 16 ; .bin defaults to 16 bits
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;; FIXME: possible problem with HEIGHT being defined
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;; as one less than what VIDEO_MODE implies?
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WIDTH equ 0x50 ; 60
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HEIGHT equ 0x18 ; 24 (?)
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VIDEO_MODE equ 0x3 ; 80x25 screen, text mode
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WIDTH equ 0x4F ; 79
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HEIGHT equ 0x18 ; 24
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VIDEO_MODE equ 0x3 ; 80x25 screen, text mode
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PIT_MODECOMMAND_PORT equ 0x43 ; programmable interval timer mode/command port (used for speaker)
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PIT_CH2_DATA_PORT equ 0x42 ; PIT channel 2 data port
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;; see http://www.ctyme.com/intr/int-10.htm for interrupts
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@ -33,128 +34,160 @@ int 0x10
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mov sp, 0x2000 ; initialise stack pointer
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.loop:
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mov ah, 0x00 ; Read character
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mov ah, 0x00 ; Read a character
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int 0x16
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cmp al, 0x0d ; newline
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je .newline
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cmp al, 0x08 ; backspace
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je change_color_mode
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cmp al, 0x08 ; delete character
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je .change_color_mode
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cmp al, 0x1b ; esc
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je beep
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cmp al, 0x1b ; escape character
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je .beep
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cmp al, 0x0d ; enter
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je .nl
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jmp .nonewline
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jmp nonewline ; all other characters
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.change_color_mode:
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call .readbyte
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mov [color_mode], al
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.nl:
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call newline
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jmp .loop
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.newline:
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;; Scroll up window
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mov ah, 0x06
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mov al, 0x01
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mov bh, 0x0F
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mov cx, 0x0000
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mov dh, HEIGHT
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mov dl, WIDTH
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int 0x10
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;; Update the color_mode variable with a byte from the keyboard
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;;
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;; CLOBBERS
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;; - ax
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;; - bl
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change_color_mode:
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call readbyte ; get byte from keyboard (in al)
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mov [color_mode], al ; store byte in color_mode variable
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;; Get current cursor position
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mov bh, 0x00
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mov ah, 0x03
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jmp start.loop
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;; Simulates going to a new line
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;;
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;; CLOBBERS
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;; - ax
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;; - bh
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;; - cx
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;; - dx
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newline:
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;; Scroll up window
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mov ah, 0x06 ; scroll screen up
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mov al, 0x01 ; lines to scroll (1)
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mov bh, 0x0F ; bg/fg colour
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mov cx, 0x0000 ; upper row num/left col num (both 0)
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mov dh, HEIGHT ; lower row num (24)
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mov dl, WIDTH ; right col num (80)
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int 0x10
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;; Move cursor to beginning of screen
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mov dl, 0x00
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mov ah, 0x02
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mov ah, 0x02 ; set cursors position
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mov bh, 0x0 ; page number
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mov dh, HEIGHT ; row
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mov dl, 0x00 ; col
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int 0x10
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jmp .loop
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ret
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.beep:
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call .readduration
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;; Plays a note on the speaker for a given duration
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;;
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;; CLOBBERS
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;; - ax
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;; - bx
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;; - cx
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beep:
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call read_duration ; get duration from keyboard (in al)
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mov ah, 0
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push ax
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mov al, 182 ; Prepare the speaker for the
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out 43h, al ; note.
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call .readbyte
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mov ah, 0
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sal ax, 5 ; multiply by 32
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push ax ; store on stack
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;; move 182 (0b10 11 011 0) into al
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;; bit 7-6 = channel select (2, PC speaker)
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;; bit 5-4 = access mode (lobyte/hibyte)
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;; bit 3-1 = operating mode (square wave generator)
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;; bit 0 = BCD/binary mode (16-bit binary)
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mov al, 0b10110110
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out PIT_MODECOMMAND_PORT, al ; write to PIT control port
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;; Read byte and convert to a usable frequency
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call readbyte ; read byte from keyboard (in al)
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mov ah, 0 ; readbyte clobbers ax
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sal ax, 5 ; multiply by 32
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add ax, 1140
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out 42h, al ; Output low byte.
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mov al, ah ; Output high byte.
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out 42h, al
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in al, 61h ; Turn on note (get value from
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; port 61h).
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or al, 00000011b ; Set bits 1 and 0.
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out 61h, al ; Send new value.
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out PIT_CH2_DATA_PORT, al ; Output low byte.
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mov al, ah
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out PIT_CH2_DATA_PORT, al ; Output high byte
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;; Port 0x61 does a whole lot but only the bottom 2 bits are relevant here
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;; (speaker enable and speaker input select)
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in al, 61h ; Preserve previous value
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or al, 00000011b ; Set bits 1 and 0 (enable speaker, input = channel 2)
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out 61h, al ; Send new value
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;; mov bx, 50000 ; Pause for duration of note.
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pop bx
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push ax
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;; multiply duration by 3125
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pop bx ; pull duration value from stack into bx
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push ax ; save ax (contains garbage?)
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mov ax, 3125
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mul bx
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mov bx, ax
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pop ax
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mul bx
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mov bx, ax ; move dur * 3125 into bx
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pop ax ; restore ax
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;; play note for a certain duration
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.pause1:
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mov cx, 65535
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mov ecx, 65535
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.pause2:
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dec cx
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jne .pause2
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dec bx
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jne .pause1
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in al, 61h ; Turn off note (get value from
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; port 61h).
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and al, 11111100b ; Reset bits 1 and 0.
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out 61h, al ; Send new value.
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jmp .loop
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dec cx ; count down
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jne .pause2 ; if not zero keep counting down
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dec bx ; decrement duration counter
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jne .pause1 ; keep doing that until it is 0
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.nonewline:
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in al, 61h ; Preserve previous value
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and al, 11111100b ; Clear bits 1 and 0 (disable speaker, clear channel select)
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out 61h, al ; Send new value
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jmp start.loop
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;; Handles all other characters by writing them to the screen
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;;
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;; CLOBBERS
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;; - ah
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;; - bx
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;; - cx
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;; - dx
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nonewline:
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;; Write character
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mov ah, 0x09
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mov bh, 0x00
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mov bl, [color_mode]
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mov cx, 0x01
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int 0x10
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mov ah, 0x09 ; write character with attribute
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mov bh, 0x00 ; page number
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mov bl, [color_mode] ; BIOS colour code
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mov cx, 0x01 ; amount of times to print character
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int 0x10
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;; Get current cursor position
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mov ah, 0x03
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;; dh = row, dl = col
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mov ah, 0x03 ; get cursor position and shape
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int 0x10
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;; if the cursor is at the edge of the screen go to the next line
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;; else move it forward once
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cmp dl, WIDTH
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jge .eol
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jmp .noeol
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.eol:
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;; Scroll up window
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mov ah, 0x06
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mov al, 0x01
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mov bh, 0x0F
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mov cx, 0x0000
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mov dh, HEIGHT
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mov dl, WIDTH
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int 0x10
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call newline
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;; Move cursor to beginning of screen
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mov bh, 0
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mov dh, HEIGHT
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mov dl, 0x00
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mov ah, 0x02
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int 0x10
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jmp .loop
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jmp start.loop
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.noeol:
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;; Move cursor forward
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inc dl
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mov ah, 0x02
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mov ah, 0x02 ; set cursor position, dh (row) already set, dl (col) updated on prev line
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int 0x10
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jmp .loop
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jmp start.loop
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;; Reads two characters from the keyboard buffer and converts them into a single byte
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;;
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@ -163,10 +196,13 @@ mov sp, 0x2000 ; initialise stack pointer
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;; the first character is shifted left by 4
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;; the shifted and non-shifted values are then or'ed together to form a byte
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;;
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;; RETURNS
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;; A byte in al
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;;
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;; CLOBBERS
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;; - ax
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;; - bl
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.readbyte:
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readbyte:
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mov ah, 0x00 ; Read character
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int 0x16
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@ -185,16 +221,24 @@ mov sp, 0x2000 ; initialise stack pointer
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ret
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.readduration:
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;; Reads a duration from the keyboard
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;;
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;; RETURNS
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;; A duration in al
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;;
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;; CLOBBERS
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;; - ax
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read_duration:
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;; Read duration (0-16 supported)
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mov ah, 0x00
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mov ah, 0x00 ; read keypress
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int 0x16
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;; Read character is in al
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sub al, 'a'
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sub al, 'a' ; normalise
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ret
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halt: hlt
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;; Variable to store color mode information for writing to the screen
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color_mode: db 0x02
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;; Magic number must be in the last 2 bytes of the sector so
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