INTRODUCTION
This code example provides a set of keyboard routines to control sound output while waiting for a user to enter a keyboard character. The advantage to this method is that a main routine can call these sound routines to play a sound sequence, and the sound routines will return control back to the main routine whenever the user enters keyboard data so that the main routine can continue computing while the sound plays in the background. The code example has two different code entry points for getting keyboard data. One code entry point is a standard get_keyinput call which will wait for a key and update the sound data until a key code is found. The other code entry point is the get_keyinput_to call, which will wait a set amount of time for a key code and if none is found, return with a no key code found condition. The calling routine puts a timeout counter value in register AX on entry. The counter value is based on the system clock which ticks at 18.2 times per second. The entry point start_table_sound is used to begin a background sound sequence. On entry, the register BX indexes a table of sound data. The table has a format of four byte entries and is terminated by a data word of zero. The four bytes are used as two words: the first is a duration count and the second is a tone value. There are two code entry points for turning the background sound off and on. There is also a utility to flush out the keyboard buffer that can be executed with a call to flush_keyboard.
;Set of keyboard routines with sound outputs
.MODEL small
.STACK 500
.DATA
;define table for sound output
;sample_sounds dw 8,45000 ;long low sound
; dw 2,2000 ;short high sound
; dw 0 ;end of sample sound table
sound_table dw 0
sound_time_m dw 0
sound_time_l dw 0
sound_flag db 0
sound_on_flag db 0,0
key_time_out_m dw 0
key_time_out_l dw 0
.CODE
;************ ^^^^^^^^^^ *************
;### code entry point #####
get_keyinput proc near
;this routine checks for keyboard data in BIOS buffer
; and returns with data if there
;else it updates sound output data and loops to check for
; keyboard data again until keyboard data found
;on exit AX has keyboard data
public get_keyinput
push bx
push cx
push dx
get_keyinput_loop:
mov ah,1 ;set AH for scan
int 16H ;BIOS Call
;branch if no keyboard data
jz sound_update
mov ah,0 ;set AH for get key
int 16H ;BIOS Call
pop dx
pop cx
pop bx
ret
;******* -------- *******
sound_update:
cmp sound_flag,0 ;check for sound on????
jz get_keyinput_loop ;branch out if sound off
mov cx,sound_time_m ;else check for sound update
mov ax,sound_time_l
call test_current_time ;is it time for update ??
jc get_keyinput_loop ;branch if not time
mov bx,sound_table
mov ax,[bx] ;get next sound update value
or ax,ax ;?? end of sound ??
jz turn_sound_off ;branch if end sound
call get_time_plus_ax ;reset sound duration
mov sound_time_m,cx
mov sound_time_l,ax
inc bx
inc bx
mov ax,[bx]
inc bx
inc bx
mov sound_table,bx
call sound_out_ax ;go set sound frequency
jmp get_keyinput_loop ;branch to keyboard loop
turn_sound_off:
call sound_off
mov sound_flag,0
jmp get_keyinput_loop ;branch to keyboard loop
get_keyinput endp
;^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
;************ ########## *************
;### code entry point #####
get_keyinput_to proc near
;get keyboard data with timeout if no data available
;on entry AX has time duration in 18 ticks per second
;on exit if carry clear then AX has keyboard data
public get_keyinput_to
push bx
push cx
push dx
call get_time_plus_ax ;add duration to current time
mov key_time_out_m,cx ;set timeout value
mov key_time_out_l,ax
get_keyinput_to_loop:
mov ah,1 ;ready to scan keyboard data
int 16H ;BIOS Call
jz sound_update_to ;branch if no keyboard data
mov ah,0 ;ready to get key data
int 16H ;BIOS Call
pop dx
pop cx
pop bx
clc ;set keyboard data flag
ret
get_keyinput_to_1:
mov cx,key_time_out_m ;check for timeout
mov ax,key_time_out_l
call test_current_time
jc get_keyinput_to_loop ;branch if no timeout
xor ax,ax ;else timeout return condition
pop dx
pop cx
pop bx
stc ;set no keyboard data flag
ret
; ******** %%%%%%% ********
sound_update_to:
cmp sound_flag,0 ;check for sound on????
jz get_keyinput_to_1 ;branch if sound off
mov cx,sound_time_m ;else check for sound update
mov ax,sound_time_l
call test_current_time
jc get_keyinput_to_1 ;branch if not ready for update
mov bx,sound_table
mov ax,[bx]
or ax,ax ;test for end of table
jz turn_sound_off_to ;branch if end of table data
call get_time_plus_ax
mov sound_time_m,cx
mov sound_time_l,ax
inc bx
inc bx
mov ax,[bx]
inc bx
inc bx
mov sound_table,bx
call sound_out_ax
jmp get_keyinput_to_1
turn_sound_off_to:
call sound_off
mov sound_flag,0
jmp get_keyinput_to_1
get_keyinput_to endp
;^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
;************ @@@@@@@@@@ ************
;### code entry point #####
start_table_sound proc near
;subroutine to start background sound output
;on entry BX indexes sound data table
public start_table_sound
push ax
push bx
mov ax,[bx]
call get_time_plus_ax
mov sound_time_m,cx
mov sound_time_l,ax
inc bx
inc bx
mov ax,[bx]
inc bx
inc bx
mov sound_table,bx
call sound_out_ax
mov sound_flag,0FFH
pop bx
pop ax
ret
start_table_sound endp
;************ ========== *************
;### code entry point #####
flush_keyboard proc near
;utility to flush contents of keyboard buffer
public flush_keyboard
mov ah,1
int 16H ;BIOS Call ;scan for keyboard data
jz flush_keyboard_x ;branch if no keyboard data
mov ah,0 ;else get keyboard data
int 16H ;BIOS Call
jmp flush_keyboard
flush_keyboard_x:
ret
flush_keyboard endp
;************* ----------- **************
sound_out_ax proc near
;set sound out frequency to data value in AX
push ax
push ax
cmp sound_on_flag,0
jne sound_out_1
in al,61H ;input port 61h
or al,3
out 61H,al ;output port 61h
sound_out_1:
mov al,0B6H
out 43H,al ;output port 43h
pop ax
out 42H,al ;output port 42h
xchg al,ah
out 42H,al ;output port 42h
mov so