;
; Interrupt-Example-Timer0-ATmega1284P.asm
; Used in the MicroController course at Ioannina
; Physics department.
; Created: 04/11/2021  by Dr. Costas Foudas
; Author : foudas
;
jmp INIT				 ; 2 word Vect RESET
nop						 ; Ext Int 0
reti					 ; 
nop						 ; Ext Int 1
reti					 ; 
nop						 ; Ext Int 2
reti					 ; 
nop						 ; PCINT 0 - Pin Change 
reti					 ; 
nop						 ; PCINT 1 - Pin Change 
reti					 ; 
nop						 ; PCINT 2 - Pin Change
reti					 ; 
nop						 ; PCINT 3 - Pin Change
reti					 ; 
nop						 ; WDT  - Watchdog Timeout
reti					 ; 
nop						 ; Timer 2 Compare A
reti					 ; 
nop						 ; Timer 2 Compare B
reti					 ; 
nop						 ; Timer 2 Overflow
reti					 ; 
nop						 ; Timer 1 Capture
reti					 ; 
nop						 ; Timer 1 Compare A
reti					 ; 
nop						 ; Timer 1 Compare B
reti				     ; 
nop						 ; Timer 1 Overflow
reti					 ; 
nop						 ; Timer 0 Compare A
reti					 ; 
nop						 ; Timer 0 Compare B
reti					 ; 
jmp T0_OF				 ; Timer 0 Overflow
nop						 ; SPI Serial Transfer Complete
reti					 ; 
nop						 ; USART0_RX  Complete
reti					 ; 
nop						 ; USART0 Data Register Empty
reti					 ; 
nop						 ; USART0_TX complete
reti					 ; 
nop						 ; Analog Comparator
reti					 ; 
nop						 ; ADC Conversion complete
reti					 ; 
nop						 ; EEPROM Ready
reti					 ; 
nop						 ; Two Wire Interface
reti					 ; 
nop						 ; Store Program Memory Ready
reti					 ; 
nop						 ; USART1 Rx Complete
reti					 ; 
nop						 ; USART1 Data Register Empty
reti					 ; 
nop						 ; USART1 Tx Complete
reti					 ; 
nop						 ; Timer/Counter 3 capture Event
reti					 ; 
nop						 ; Timer/Counter 3 Compare A
reti					 ; 
nop						 ; Timer/Counter 3 Compare B
reti					 ; 
nop						 ; Timer/Couner  3 Overflow
reti                     ; 
;
INIT:
;
CLI           ; Disable interrupts during initialization
;
; THE NEXT 4 LINES LOAD THE STACK POINTER WITH THE ADDRESS
; OF THE BOTTOM OF THE SRAM
;
LDI R16, HIGH(RAMEND)
OUT SPH, R16
LDI R16, LOW(RAMEND)
OUT SPL, R16
;
; MAKE PORTB AN OUTPUT PORT
;
LDI R16, $FF
OUT DDRB, R16
;
;
LDI R16, $00
out TCCR0A, R16  ; NORMAL OPERATION NO PWM
LDI R16, $05
OUT TCCR0B, R16  ; NO PWM AND PRESCALE THE 32 KHZ CLOCK BY 1024 
LDI R16, $01
STS TIMSK0, R16  ; ENABLE TIMER0/COUNTER0 OVERFLOW INTERRUPT
;
; Initializing counter registers....
;
LDI R18, $00     ; THIS HAS THE INCREMENTING NUMBERS TO BE SENT TO PORTB
LDI R17, $00     ; THIS COUNTS THE NUMBER OF INTERRUPTS
;
SEI   ; ENABLE INTERRUPTS
;
START:           ; LOOP AROUND START FOR EVER 
	nop          ; do nothing
	nop          ; do nothing
RJMP START

T0_OF:           ; INTERRUPT SERVICE ROUTINE FOR TIMER/COUNTER 0 OVERFLOW
   ;
   CLI           ; DISABLE INTERRUPTS
   IN R19, SREG  ; STORE SREG CONTENTS ON R19
                 ; SO THAT YOU CAN RESTORE SREG AFTER
				 ; THE INTERRUPT SERVICE ROUTINE HAS BEEN EXECUTED
  ;
  INC R17        ; COUNT INTERRUPTS
  CPI R17, $15   ; EVERY 21 INTERRUPTS SEND AN INCREMENTING NUMBER FROM
                 ; R18 TO THE LEDS OF PORTB
  BRNE AGAIN
  CLR R17
  ;
  OUT PORTB, R18
  INC R18
AGAIN:
  OUT SREG,r19  ; RESTORE SREG
  SEI           ; ENABLE INTERRUPTS AGAIN
  RETI          ; GO BACK TO WHAT YOU WERE DOING AT 
                ; THE TIME OF THE INTERRUPT