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 tablesound_table    dw   0sound_time_m   dw   0sound_time_l   dw   0sound_flag     db   0sound_on_flag  db   0,0key_time_out_m dw   0key_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 dxget_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 loopturn_sound_off:     call sound_off     mov  sound_flag,0     jmp  get_keyinput_loop  ;branch to keyboard loopget_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,axget_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     retget_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_1turn_sound_off_to:     call sound_off     mov  sound_flag,0     jmp  get_keyinput_to_1get_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     retstart_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_keyboardflush_keyboard_x:     retflush_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 61hsound_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  sound_on_flag,0FFH     pop  ax     retsound_out_ax   endp;***********  $$$$$$$$$$  ************;###### code entry point #######sound_off proc near   ;turn sound port off     public    sound_off     push ax     cmp  sound_on_flag,0     je   sound_off_exit     in   al,61H         ;input port 61h     and  al,0FCH     out  61H,al         ;output port 61h     mov  sound_on_flag,0sound_off_exit:     pop  ax     retsound_off endp;**************  %%%%%%%%%%  ***************;with all CX:AX time values, CX is most significant ; and AX is least significantget_current_time    proc near;on exit CX:AX has 32 bit day clock value ; in 18.2 ticks per second     push dx          xor  ax,ax     ;set AH to zero          int  1AH       ;BIOS Call get time          mov  ax,dx     pop  dx     retget_current_time    endp;****************************get_time_plus_ax    proc near;on entry AX has 16 bit value to add to current clock time;on exit CX:AX has new 32 bit clock value     push dx     push ax     xor  ax,ax     int  1AH            ;BIOS Call     pop  ax     add  ax,dx     adc  cx,0     pop  dx     retget_time_plus_ax    endp;************  ########  ************test_current_time   proc near;on entry CX:AX has time value ; to be subtracted from the current time;on exit if carry set then current time ; is less than CX:AX time     push dx     push cx     push ax     xor  ax,ax     int  1AH            ;BIOS Call     cmp  dx,18     jb   test_current_time_2test_current_time_1:     pop  ax     sub  dx,ax     pop  dx     sbb  cx,dx     mov  cx,dx     pop  dx     rettest_current_time_2:     or   cx,cx     jnz  test_current_time_1     pop  ax      ;this is fix code for midnight factor     pop  dx     pop  dx     clc          ;clear carry condition     rettest_current_time   endp;*****************************************     end