;kitchen.asm
;PortB Connects to 2 Thumb wheel switches
;This allows the user to enter the required
;data as minutes and is read by the processor
;as BCD input

;LED on PD0 lights up for 50 ms every second
;A buzzer on PD1 goes off at the end of the present
;time.

;Usage: set the required number of minutes on the
;thumb wheel switches (0 to 99 minutes) and press
;RESET switch. The timer is now armed and will
;activate the buzzer at the end of the period.

;Dhananjay V. Gadre
;9th April 1999



.include "1200def.inc"

.def sec=r19
.def minute=r20
.def time=r21
.def save_status=r0

.cseg
.org 0
        rjmp    RESET           ;Reset Handle
        rjmp    Timer_int
        rjmp    Timer_int

RESET: ldi r16, 0b00000101 ; DIV1024 selected for timer0
       out TCCR0, r16      ; timer 0 counts up now

       ldi r16, 2
       out TIMSK, r16

       ldi r16, -175      ; -195 gives 50 ms on 4 MHz
       out TCNT0, r16     ; -175 gives 50 ms on 3.58 MHz


       ldi r16, 0 ;configure PORT B for all inputs
       out DDRB, r16

       ldi r16, 255 ; put on the pull ups on PORTB so that the
                    ; switches can be read
       out PORTB, r16
       

       ldi r16, 255
       out DDRD, r16         ;configure pin PD0 as output

       ldi r16, $ff          ; everything on PORTD is off
       out PORTD, r16

       ldi sec, 0
       ldi minute, 0
       ldi time, 0
       sei

get_t:    in r16, PINB
          com r16
          rcall get_value

compare:  cp r16, time 
          brne compare
outit:    cbi PORTD, 1
          rjmp outit
          rjmp outit






Timer_int:  in save_status, SREG
            sbi PORTD, 0 ; put off PD0 led if it was on
            ldi r23, -175  ; actually -195  for 4 MHz
                           ;-175 for 3.58 MHz
            out TCNT0, r23
            inc sec
            cpi sec, 20              ;20 in sec means 1 second
            brne go_bak
            cbi PORTD, 0             ; light up PD0 LED
            ldi sec, 0
            inc minute
            cpi minute, 60
            brne go_bak
            ldi minute, 0
            inc time
go_bak:     out SREG, save_status
            reti


;subroutine to convert the BCD value in register r16
;to a hex value.
;Destroys r17 and r18 contents

get_value: in save_status, SREG
           cpi r16, 0
           breq no_good
           mov r17, r16
           andi r17, $0f
           andi r16, $f0
           swap r16         ; get r16 higher nibble to
                            ; lower nibble place
           mov r18, r16
           lsl r16
           lsl r16
           lsl r16
           add r16, r18
           add r16, r18
           add r16, r17
           cpi r16, 100 ; check that the result is less than 99
           brlo no_good ;less than 100. so fine, go return
           ldi r16, 01  ; no, then put in 01
no_good:   out SREG, save_status
           ret