Reverse Code Engineering RCE CD +sandman 2000/ReverseCodeEngineeringRceCdsandman2000.iso/RCE/Library/Manuels & Misc/Assembly/AOA.ZIP/CH10/EX10_1.ASM

Assembly Source File | 1996-02-08 | 4.2 KB | 277 lines

; Ex10_1.asm
;
; Software that plays Musical notes.
; Intended for use with Chapter 10 Laboratory Experiments


        .xlist
        include     stdlib.a
        includelib    stdlib.lib
        .list

; Hardware related equates

PPI_B        equ    61h        ;8255 port B address
PIT_Ch2        equ    42h        ;Timer channel 2 address
PIT_CW        equ    43h        ;Timer control word address.

RTC        textequ    <es:[6ch]>    ;Real Time clock writes here.





; The following macros program the 8254 timer chip to play a
; note or a rest.

Note        macro    frequency, duration
        mov    ax, frequency
        mov    cx, duration
        call    PlayNote
        endm

Rest        macro    Duration
        local    RestLoop

;; Turn off the speaker.

        in    al, PPI_B
        and    al, 0FCh
        out    PPI_B, al

        mov    cx, Duration
RestLoop:    call    Delay18
        loop    RestLoop
        endm




dseg        segment    para public 'data'

; See Delay18.asm for details about the following variables.

TimedValue    word    0
RTC2        word    0


; DivisorConst is the constant that, when divided by a desired frequency
; produces the divisor constant to feed into the timer chip to produce
; a tone of the given frequency.

DivisorConst    dword    1193180


dseg        ends

;********************************************************





cseg        segment    para public 'code'
        assume    cs:cseg, ds:dseg

; Delay- This routine delays for approximately 1/18th second.
;      See the Delay18.asm file for comments about this code.

Delay18        proc    near
        push    ds
        push    es
        push    ax
        push    bx
        push    cx
        push    dx
        push    si

        mov    ax, dseg
        mov    es, ax
        mov    ds, ax
        mov    cx, TimedValue
        mov    si, es:RTC2
        mov    dx, PPI_B

        align    4
TimeRTC:    mov    bx, 50
        align    4
DelayLp:    dec    bx
        jne    DelayLp
        cmp    si, es:RTC2
        loope    TimeRTC

        pop    si
        pop    dx
        pop    cx
        pop    bx
        pop    ax
        pop    es
        pop    ds
        ret
Delay18        endp



; DelayInit-    Computes the timing constant for the Delay18 routine
;        by watching when the RTC code updates the RTC variable.

DelayInit    proc
        push    es
        push    ax
        push    bx
        push    cx
        push    dx
        push    si

        mov    ax, 40h
        mov    es, ax
        mov    ax, RTC
RTCMustChange:    cmp    ax, RTC
        je    RTCMustChange

        mov    cx, 0
        mov    si, RTC
        mov    dx, PPI_B
        align    4
TimeRTC:    mov    bx, 50
        align    4
DelayLp:    dec    bx
        jne    DelayLp
        cmp    si, RTC
        loope    TimeRTC

        neg    cx            ;CX counted down!
        shl    cx, 1            ;Increase delay time.
        mov    TimedValue, cx        ;Save away

        pop    si
        pop    dx
        pop    cx
        pop    bx
        pop    ax
        pop    es
        ret
DelayInit    endp





; PlayNote-    This procedure programs the 8254 timer chip to play a given
;        note (frequency is passed in AX) for a given duration (passed
;        in cx).

PlayNote    proc
        push    dx
        push    cx
        push    ax

; Turn on the speaker.

        in    al, PPI_B
        or    al, 3
        out    PPI_B, al

; Tell the chip we want to program it with a new 16-bit divisor value.

        mov    al, 0B6h    ;Magic value to program chip.
        out    PIT_CW, al

; Convert the frequency to a divisor constant.

        pop    cx        ;Get the frequency.

        mov    dx, word ptr DivisorConst+2
        mov    ax, word ptr DivisorConst
        div    cx

        out    PIT_Ch2, al
        xchg    al, ah
        out    PIT_Ch2, al

        mov    ax, cx        ;Restore original AX value.
        pop    cx        ;Retrieve duration
        mov    dx, cx        ;Save Duration.
DelayLp:    call    Delay18
        loop    DelayLp
        mov    cx, dx        ;Restore original CX value

        pop    dx        ;Restore original DX value.
        ret
PlayNote    endp


; Main program which tests out the DELAY subroutine.

Main        proc
        mov    ax, dseg
        mov    ds, ax
        mov    es, ax

        call    DelayInit

; Play "Amazing Grace"

        note    294, 4
        note    392, 8
        note    494, 2
        note    392, 2
        note    494, 8
        note    440, 4
        note    392, 8
        note    330, 4
        note    294, 8
        rest    2
        note    294, 4
        note    392, 8
        note    494, 2
        note    392, 2
        note    494, 8
        note    440, 4
        note    587, 16

        note    494, 4
        note    587, 4
        note    494, 2
        note    587, 2
        note    494, 2
        note    392, 8
        note    294, 4
        note    330, 4
        note    392, 2
        rest    2
        note    392, 2
        note    330, 2
        note    294, 8
        rest    2
        note    294, 4
        note     392, 8
        note    494, 2
        note    392, 2
        note    494, 8
        note    440, 4
        note    392, 16


        rest    1



Quit:        ExitPgm            ;DOS macro to quit program.
Main        endp







cseg            ends



sseg        segment    para stack 'stack'
stk        dw    1024 dup (0)
sseg        ends
        end    Main