; ******************************************************************
; * Music on an STK200, using a R/2R network for playing tunes     *
; * PortD has eight keys (active low), PortB generates the         *
; * output for the R/2R-network, plays notes when key is activated *
; * ATMEL AT90S8515 at 4 Mcs/s                                     *
; * (C)2005 by http://www.avr-asm-tutorial.net                     *
; ******************************************************************
;
.NOLIST
.INCLUDE "8515def.inc"
.LIST
;
; Constants
;
.EQU clock = 4000000 ; processor clock
.EQU cNSine = 32 ; Table length of sine wave
;
.DEF rLen = R1 ; length of delay for the sine wave
.DEF rCnt = R2 ; Counter for length delay
.DEF rmp = R16 ; multi purpose register
.DEF rTab = R17 ; counter for table length
;
	ldi rmp,0xFF ; all bits of port B = output => R/2R network
	out DDRB,rmp ; set data direction register
wtloop:
	in rmp,PIND ; read the keys
	cpi rmp,0xFF ; all keys inactive?
	breq wtloop ; yes, wait until active
	ldi ZH,HIGH(2*MusicTable) ; Point Z to music table
	ldi ZL,LOW(2*MusicTable)
tabloop:
	rol rmp ; rotate next lowest bit into carry
	brcc tabfound ; found that key pressed
	adiw ZL,1 ; point Z to next table value
	rjmp tabloop ; check next bit
tabfound:
	lpm ; read music table value to R0
	mov rlen,R0 ; copy to delay, R0 used otherwise
;
; Play a tone until all keys are inactive
;
startsine:
	ldi ZH,HIGH(2*SineTable) ; Set Z to sine wave table
	ldi ZL,LOW(2*SineTable)
	ldi rTab,cNSine ; Length of SineWave table
;
; The following code is optimized for reaching equal runtimes
; for all loop runs, clocks cycles needed are calculated
; for all instructions after their execution,
; clock cycles during table read / clock cycles at table end
;
loopsine:
	in rmp,PIND ; 1/- Check if input still active
	cpi rmp,0xFF ; 2/-
	breq wtloop ; 3/- key not active any more, restart
	nop ; 4/- delay to synchronize
loopnext:
	lpm ; 7/3 read sinewave value to R0
	out PORTB,R0 ; 8/4 copy to R/2R network
	mov rCnt,rLen ; 9/5 Set delay counter value
; delay loop, requires 3*rLen-1 clock cycles
loopdelay:
	dec rCnt ; (1) next counter value
	brne loopdelay ; (2/1) not yet zero
; 3*rLen+8/3*rLen+4 at end of delay loop
	adiw ZL,1 ; 3*rLen+10/3*rLen+6 next value in table
	dec rTab ; 3*rLen+11/3*rLen+7 table counter
	brne loopsine ; 3*rLen+13/3*rLen+8 play next value in table
	ldi ZH,HIGH(2*SineTable) ; -/3*rLen+9 reload first table value
	ldi ZL,LOW(2*SineTable) ; -/3*rLen+10
	ldi rTab,cNSine ; -/3*rLen+11 Length of sine wave table
	rjmp loopnext ; -/3*rLen+13 restart loop
;
; Table for delays to generate the 8 different frequencies
;
; frequency = clock / TableLength / ( 3 * rLen + 13 )
; rLen = ( clock /TableLength / frequency - 13 ) / 3
;
MusicTable:
; f=261.6 293.7 329.6 349.2 392.0 440.0 493.9 523.2 (should be)
.DB 155,  138,  122,  115,  102,  90,   80,   75
; f=261.5 292.7 329.8 349.2 391.9 441.7 494.1 525.2 (is really)
; differences caused by rounding and limited resolution)
;
; Sinewave table for 8 bit D/A
; Table length = 32 values
; VCC=5.000V, uLow=0.000V, uHigh=2.500V
; (generated by sinewave.pas)
;
Sinetable:
.DB 64,76,88,99,109,117,123,126
.DB 128,126,123,117,109,99,88,76
.DB 64,51,39,28,19,11,5,1
.DB 0,1,5,11,19,28,39,51
;
; End of program
;