;  Boot beep routine
;
;   Called with RTS6  A3 must be set up  w/ memory offset (overlay)
;           D3 contains the duration: 40 is boot beep

; make an attractive beep to tell the world that the CPU works.  Use
; Charlie Kellner's filter algorithm.  First fill the waveForm buffer
; with the initial waveForm.

BootBeep
        MOVE.L  #VBase,A5       ; get the VIA base address
        BCLR    #7,VBufB(A5)    ;enable the sound

        LEA SoundLow,A0 ; get sound buffer address
        ADD.L   A3,A0       ; overlay bit is on, so offset
        MOVE.L  A0,A4       ; keep soundBase in A4

        MOVEQ   #4,D0       ; repeat 74 byte sequence 5 times
@3
        MOVE.L  #$FA40C006,D1 ; 4 byte table to fill buffer with
@2
        MOVEQ   #19,D2      ; repeat 19 times
@1
        MOVE.B  D1,(A0)     ; move in a byte
        ADDQ    #2,A0       ; bump to next buffer location
        SUBQ    #1,D2       ; done 19 times yet?
        BNE.S   @1          ; if not, loop

        LSR.L   #8,D1       ; get next byte value
        BNE.S   @2          ; fill next 18 values

        DBRA    D0,@3       ; repeat the whole sequence 5 times

; OK, now filter it for a nice fade -- repeat the filtering process D3 times
; note that D1 and D2 are zero at this point

FLoop0
        MOVE.L  A4,A0       ; point A0 to start of buffer
        LEA 146(A0),A1      ; point A1 74 values in
        MOVEQ   #73,D0      ; process 74 samples
FLoop1
        MOVE.B  (A1),D2     ; get 74th value
        ADDQ    #4,A1       ; bump to 76th value
        MOVE.B  (A1),D1     ; make it a word value
        ADD.W   D1,D2       ; add to the accumulator
        SUBQ    #2,A1       ; point at 75th value
        MOVE.B  (A1),D1     ; get it
        ADD.W   D1,D2       ; add to accumulator
        ADD.W   D1,D2       ; count it twice

        ADDQ    #3,D2       ; add 3 to round off
        ASR #2,D2           ; divide it by 4
        MOVE.B  D2,(A0)     ; store it away
        ADDQ    #2,A0       ; bump to next value
        DBRA    D0,FLoop1   ; loop for all 74 values

; now copy first 74 values into the rest of the buffer

FillIt
        MOVE    #295,D0         ; 296 values to copy
FLoop2
        MOVE.B  -74(A0),(A0)    ; move in next value
        ADDQ    #2,A0
        DBRA    D0,FLoop2       ; loop till done

; now wait for blanking before repeating

EndLoop
        MOVE.W  #5500,D0        ; init timeout factor
@1
        BTST    #1,VIFR(A5) ; is VBL on?
        DBNE    D0,@1       ; wait for it to come on
        MOVE.B  #$02,VIFR(A5)   ; mask it off

        DBRA    D3,FLoop0       ; repeat D3 times

; all done with our boot beep so turn down the sound

        BSET    #7,VBufB(A5)    ;disable the sound

        RTS6