Category : Music and Digitized Voice
Archive   : VOCSHOW.ZIP
Filename : PC_SOUND.ASM

package assembly pc_sound is

if memory_model = 0 then
pragma memory_model(0);
else
pragma memory_model(1);
end if;

CSEG
jmp main -- jump to initialization

DSEG
prevwhistle db ?
a_sample_duration dw ?
on_off_bytes db 256 dup(?)

CSEG
on_off_pattern equ $
dw 2#00000000_11111111# -- 0 nibbles are in sign+magnitude form
dw 2#00000001_11111111# -- 1
dw 2#00000011_11111111# -- 2
dw 2#00000111_11111111# -- 3
dw 2#00001111_11111111# -- 4
dw 2#00011111_11111111# -- 5
dw 2#00111111_11111111# -- 6
dw 2#01111111_11111111# -- 7
dw 2#00000000_11111110# -- -1
dw 2#00000000_01111110# -- -2
dw 2#00000000_00111110# -- -3
dw 2#00000000_00011110# -- -4
dw 2#00000000_00001110# -- -5
dw 2#00000000_00000110# -- -6
dw 2#00000000_00000010# -- -7
dw 2#00000000_00000000# -- -8

get_ticks: -- return current tick count in ax
xor al,al
pushf -- save int enable status
cli -- lock out interrupts
out 43h,al -- read counter 0
jmp short gtl -- (don't go too fast)
gtl:
in al,40h -- get lsb of timer
xchg ah,al --
jmp short gth -- (don't go too fast)
gth:
in al,40h -- get msb of timer
xchg ah,al --
popf -- restore int enable status
ret

play_ax_till_dx: -- destroys ax,bx
-- high nibble of al contains amplitude
-- dx contains timeout value
mov bx,on_off_bytes
add bx,ax
xchg si,bx
even
pbd_loop: -- output 16 speaker on/off bytes, then,
push dx -- if we haven't timed out, do it again
mov dx,61h
lodsw
out dx,al
mov al,ah
out dx,al
lodsw
out dx,al
mov al,ah
out dx,al
lodsw
out dx,al
mov al,ah
out dx,al
lodsw
out dx,al
mov al,ah
out dx,al
lodsw
out dx,al
mov al,ah
out dx,al
lodsw
out dx,al
mov al,ah
out dx,al
lodsw
out dx,al
mov al,ah
out dx,al
lodsw
out dx,al
xor al,al
pushf -- save int enable status
cli -- lock out interrupts
out 43h,al -- read counter 0
mov al,ah
out dx,al
in al,40h -- get lsb of timer
xchg ah,al --
sub si,16
in al,40h -- get msb of timer
xchg ah,al --
popf -- restore int enable status
pop dx
cmp ax,dx
jns pbd_loop
xchg si,bx
ret

play_it_out:
-- ds:si => sound block
-- cx => N of bytes in sound block
-- destroys ax,bx,dx and si,cx
call get_ticks
mov dx,ax
cld
play_it_out_loop:
mov al,es:[si]
and ax,16#00F0#;
sub dx,[a_sample_duration]
call play_ax_till_dx
mov al,es:[si]
inc si
and ax,16#000F#
shl al,1
shl al,1
shl al,1
shl al,1
sub dx,[a_sample_duration]
call play_ax_till_dx
loop play_it_out_loop
mov al,[prevwhistle]
out 61h,al
ret

procedure set_sample_rate(samples_per_second:in sample_rates) is
pop ax -- save ret address
if memory_model = 1 then
pop dx
end if;
pop cx -- cx:=sound_length
if memory_model = 1 then -- restore ret address
push dx
end if;
push ax
mov ax,13532 -- dx:ax := 1193180
mov dx,18
div cx
mov [a_sample_duration],ax
if memory_model = 0 then
ret
else
ret far
end if;
end set_sample_rate;

procedure playback(sound:in system.address;sound_length:in natural) is
-- clobbers ax,bx,cx,dx,si
pop ax -- save ret address
if memory_model = 1 then
pop dx
end if;
pop cx -- cx:=sound_length
pop si -- si:=sound(sound'first)'address
mov bx,es
les si,lword ptr[si]
if memory_model = 1 then -- restore ret address
push dx
end if;
push ax
push bx
call play_it_out
pop es
if memory_model = 0 then
ret
else
ret far
end if;
end playback;

main:
mov ax,149 -- default sample rate:=8K
mov [a_sample_duration],ax
in al,61h
mov [prevwhistle],al
and al,16#FD#
mov bl,al -- fill on_off_bytes with 16 lists of 16
mov di,on_off_bytes -- speaker control bytes, on and off matching
mov cx,16 -- the bits in on_off_pattern
cld
mov si,on_off_pattern
amplitude_loop:
push cx
seg cs
lodsw
mov cx,16
bit_loop:
mov bh,2 -- bh:=non_speaker_bits | one bit from ax
and bh,al
or bh,bl
mov [di],bh
inc di
ror ax,1
loop bit_loop
pop cx
loop amplitude_loop
end pc_sound;