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add documentation

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Tibo 2021-10-04 17:59:48 +02:00
parent a8a7a3d3d1
commit 3ca4ce76f0
1 changed files with 150 additions and 131 deletions
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281
messages.asm
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@ -1,9 +1,11 @@
org 0x7C00 org 0x7C00 ; The boot code on a drive always gets loaded at address 0x7C00
bits 16 bits 16 ; .bin defaults to 16 bits
WIDTH equ 0x50 ;; FIXME: possible problem with HEIGHT being defined
HEIGHT equ 0x18 ;; as one less than what VIDEO_MODE implies?
VIDEO_MODE equ 0x3 WIDTH equ 0x50 ; 60
HEIGHT equ 0x18 ; 24 (?)
VIDEO_MODE equ 0x3 ; 80x25 screen, text mode
;; see http://www.ctyme.com/intr/int-10.htm for interrupts ;; see http://www.ctyme.com/intr/int-10.htm for interrupts
@ -13,173 +15,190 @@ mov ax, VIDEO_MODE
int 10h int 10h
;; Clear screen ;; Clear screen
mov ah, 0x06 mov ah, 0x06 ; scroll screen up
mov al, 0x00 mov al, 0x00 ; lines to scroll (0 = clear)
mov bh, 0x0F mov bh, 0x0F ; bg/fg colour
mov cx, 0x0000 mov cx, 0x0000 ; upper row number, left col number (both 0)
mov dh, HEIGHT mov dh, HEIGHT ; lower row number (24)
mov dl, WIDTH mov dl, WIDTH ; right col number (80)
int 0x10 int 0x10
;; Set cursor to bottom of screen ;; Set cursor to bottom of screen
mov dh, HEIGHT mov ah, 0x02 ; set cursor position
mov dl, 0x00 mov bh, 0x00 ; page number
mov bh, 0x00 mov dh, HEIGHT ; row (bottommost row)
mov ah, 0x02 mov dl, 0x00 ; col (leftmost col)
int 0x10 int 0x10
mov sp, 0x2000
mov sp, 0x2000 ; initialise stack pointer
.loop: .loop:
;; Read character mov ah, 0x00 ; Read character
mov ah, 0x00 int 0x16
int 0x16
cmp al, 0x0d ; newline cmp al, 0x0d ; newline
je .newline je .newline
cmp al, 0x08 ; delete character
je .change_color_mode cmp al, 0x08 ; delete character
cmp al, 0x1b ; escape character je .change_color_mode
je .beep
jmp .nonewline cmp al, 0x1b ; escape character
je .beep
jmp .nonewline
.change_color_mode: .change_color_mode:
call .readbyte call .readbyte
mov [color_mode], al mov [color_mode], al
jmp .loop jmp .loop
.newline: .newline:
;; Scroll up window ;; Scroll up window
mov ah, 0x06 mov ah, 0x06
mov al, 0x01 mov al, 0x01
mov bh, 0x0F mov bh, 0x0F
mov cx, 0x0000 mov cx, 0x0000
mov dh, HEIGHT mov dh, HEIGHT
mov dl, WIDTH mov dl, WIDTH
int 0x10 int 0x10
;; Get current cursor position ;; Get current cursor position
mov bh, 0x00 mov bh, 0x00
mov ah, 0x03 mov ah, 0x03
int 0x10 int 0x10
;; Move cursor to beginning of screen ;; Move cursor to beginning of screen
mov dl, 0x00 mov dl, 0x00
mov ah, 0x02 mov ah, 0x02
int 0x10 int 0x10
jmp .loop jmp .loop
.beep: .beep:
call .readduration call .readduration
mov ah, 0 mov ah, 0
push ax push ax
mov al, 182 ; Prepare the speaker for the mov al, 182 ; Prepare the speaker for the
out 43h, al ; note. out 43h, al ; note.
call .readbyte call .readbyte
mov ah, 0 mov ah, 0
sal ax, 5 ; multiply by 32 sal ax, 5 ; multiply by 32
add ax, 1140 add ax, 1140
out 42h, al ; Output low byte. out 42h, al ; Output low byte.
mov al, ah ; Output high byte. mov al, ah ; Output high byte.
out 42h, al out 42h, al
in al, 61h ; Turn on note (get value from in al, 61h ; Turn on note (get value from
; port 61h). ; port 61h).
or al, 00000011b ; Set bits 1 and 0. or al, 00000011b ; Set bits 1 and 0.
out 61h, al ; Send new value. out 61h, al ; Send new value.
;; mov bx, 50000 ; Pause for duration of note. ;; mov bx, 50000 ; Pause for duration of note.
pop bx pop bx
push ax push ax
mov ax, 3125 mov ax, 3125
mul bx mul bx
mov bx, ax mov bx, ax
pop ax pop ax
.pause1: .pause1:
mov cx, 65535 mov cx, 65535
.pause2: .pause2:
dec cx dec cx
jne .pause2 jne .pause2
dec bx dec bx
jne .pause1 jne .pause1
in al, 61h ; Turn off note (get value from in al, 61h ; Turn off note (get value from
; port 61h). ; port 61h).
and al, 11111100b ; Reset bits 1 and 0. and al, 11111100b ; Reset bits 1 and 0.
out 61h, al ; Send new value. out 61h, al ; Send new value.
jmp .loop jmp .loop
.nonewline: .nonewline:
;; Write character ;; Write character
mov ah, 0x09 mov ah, 0x09
mov bh, 0x00 mov bh, 0x00
mov bl, [color_mode] mov bl, [color_mode]
mov cx, 0x01 mov cx, 0x01
int 0x10 int 0x10
;; Get current cursor position ;; Get current cursor position
mov ah, 0x03 mov ah, 0x03
int 0x10 int 0x10
cmp dl, WIDTH cmp dl, WIDTH
jge .eol jge .eol
jmp .noeol jmp .noeol
.eol: .eol:
;; Scroll up window ;; Scroll up window
mov ah, 0x06 mov ah, 0x06
mov al, 0x01 mov al, 0x01
mov bh, 0x0F mov bh, 0x0F
mov cx, 0x0000 mov cx, 0x0000
mov dh, HEIGHT mov dh, HEIGHT
mov dl, WIDTH mov dl, WIDTH
int 0x10 int 0x10
;; Move cursor to beginning of screen ;; Move cursor to beginning of screen
mov bh, 0 mov bh, 0
mov dh, HEIGHT mov dh, HEIGHT
mov dl, 0x00 mov dl, 0x00
mov ah, 0x02 mov ah, 0x02
int 0x10 int 0x10
jmp .loop jmp .loop
.noeol: .noeol:
;; Move cursor forward ;; Move cursor forward
inc dl inc dl
mov ah, 0x02 mov ah, 0x02
int 0x10 int 0x10
jmp .loop jmp .loop
;; Reads two characters from the keyboard buffer and converts them into a single byte
;;
;; The conversion happens as follows:
;; ASCII 'a' is subtracted from each character (so 'a' = 0, 'b' = 1, ...)
;; the first character is shifted left by 4
;; the shifted and non-shifted values are then or'ed together to form a byte
;;
;; CLOBBERS
;; - ax
;; - bl
.readbyte: .readbyte:
;; Read character mov ah, 0x00 ; Read character
mov ah, 0x00 int 0x16
int 0x16
;; Read character is in al
sub al, 'a'
mov bl, al
shl bl, 0x4
;; Read character ;; Read character is in al
mov ah, 0x00 sub al, 'a' ; Normalise
int 0x16 mov bl, al
;; Read character is in al shl bl, 0x4 ; First character is upper 4 bits
sub al, 'a'
or al, bl mov ah, 0x00 ; Read character
ret int 0x16
;; Read character is in al
sub al, 'a' ; Normalise
or al, bl ; Combine both characters
ret
.readduration: .readduration:
;; Read duration (0-16 supported) ;; Read duration (0-16 supported)
mov ah, 0x00 mov ah, 0x00
int 0x16 int 0x16
;; Read character is in al ;; Read character is in al
sub al, 'a' sub al, 'a'
ret ret
halt: hlt halt: hlt
color_mode: db 0x02 color_mode: db 0x02
;; Magic number must be in the last 2 bytes of the sector so
;; fill the binary with zeroes until it is 510 bytes in size
;; (magic number will use up the remaining 2)
times 510 - ($ - $$) db 0 times 510 - ($ - $$) db 0
dw 0xAA55 dw 0xAA55 ;; Magic number to mark sector as bootable