; Progressive Display of LEDs from Input of ADC
; 06 Jul 2007       Jeffrey Drake

; Using ATtiny15L chip

.include "tn15def.inc"

.def LEDS = r16 ; temporary register
.def Delay = r17 ; Delay variable 1
.def Delay2 = r18 ; Delay variable 2
.def ADCSET = r19 ; for ADC setup

.org 0x0000  ; interrupt table
    rjmp SETUP


SETUP:
;    ser LEDS
;    cbr LEDS, 1         ; PB5 is for ADC
    ldi LEDS, 0x1F
    out DDRB, LEDS      ; set portb to output

    ldi ADCSET, 0x80    ; ADCSR: Enable
    out ADCSR, ADCSET

    ldi ADCSET, 0x80    ; load ADMUX: REFS = 10, PB5, LAR=0
    out ADMUX, ADCSET

    ldi ADCSET, 0xE0    ; load ADCSR: Enable, Start and Free run
    out ADCSR, ADCSET

STARTUP:

    


LOOP:
    ; read ADC value (low first, then high)
	in ZL, ADCL
	in ZH, ADCH
    
    rcall ADC2LED ; translate to LED mapping
    com LEDS      ; invert, as 0 is on.

    rcall UPDATE

    rcall REST
    rcall REST
    rcall REST

    rjmp LOOP ; repeat loop forever

ADC2LED:

; Converts the ADC output (1V design, 2.56V ref, 0 to 400) to 
; counter of upto 5 LEDs.
; 
; Expects Z to contain 0 to 400
; Range is halved for 8 bit processing

; Outputs Xl for bits of LED outputs.

; Mapping ADC to [LEDS]

; 0   40   80   120   160  200
; [ 1 ][ 2 ][ 3 ] [ 4 ] [ 5 ]

;      State Diagram
;         <     >=
;           120
;          /   \
;        80     \
;       /  \     \
;     40    S3   160
;    /  \       /   \
;   S1  S2     S4    S5

; LEDs are progressively lit, thus S3 = 7 or 111b


    ; divide by two    
    lsr zh ; carries over to...
    ror zl

    ; jump if < 120
    cpi zl, 120     
    brlo state3

    ; jif < 160 (>=120)
    cpi zl, 160     
    brlo state4

state5:
    ldi LEDS, 31        ; 5 leds active, 160 >= x > 200
	ret

state4:
    ldi LEDS, 15        ; 4 leds active, 120 >= x > 160
    ret

state3:
    ; jif < 80
    cpi zl, 80      
    brlo state2

    ldi LEDS, 7         ; 3 leds active, 80 >= x > 120
    ret

state2:
    ; jif < 40
    cpi zl, 40      
    brlo state1    

    ldi LEDS, 3         ; 2 leds active, 40 >= x > 80
    ret

state1:
    ldi LEDS, 1         ; 1 led active, 0 >= x > 40
    ret

    
UPDATE:
    out PORTB, LEDS     ; update LEDs    
    ret

REST:
    dec Delay
    brne REST
    dec Delay2
    brne REST

    clr Delay
    clr Delay2

    ret