;
; pwm_v1.asm
;
; Created: 21/04/2025 13:31:25
; Author : Bemposta
;

 .EQU Clock = 16000000 ;processor’s clock frequency, Hz
 .EQU Baud = 9600 ;desired serial port baud rate (bits per second)
 .EQU UBRRvalue = Clock/(Baud*16) -1 ;calculates value to be put in UBRR0H:L

 .DSEG
    valorPWM: .byte 1

 .CSEG
 .ORG 0x00000 ;reset interrupt vector
      jmp Start
 .ORG URXCaddr ; 0x00024  -> interrupt vectors for USART0
      jmp USART0_reception_completed

.ORG INT_VECTORS_SIZE ;leave room for IRQ vectors
Start:
    ldi r16, 0xFF
    out ddrd, r16

    ldi r18, (2<<COM0A0) | (1<<WGM00)
    out TCCR0A, r18
    ldi r18, (0<<WGM02) | (3<<CS00)
    out TCCR0B, r18

    ldi r20, 0      ;registro resevado para la PWM. No se debe hacer asi!!!!!!
    sts valorPWM, r20
    out ocr0a, r20

    ;configure USART0
    RCALL init_USART0
    SEI ;enable interrupts globally

Loop:
    ;nothing to do here, just be alive
    NOP
    rjmp Loop


init_USART0:
    PUSH R16
    LDI R16, LOW(UBRRvalue)
    STS UBRR0L, R16   ;load the low byte
    LDI R16, HIGH(UBRRvalue)
    STS UBRR0H, R16   ;load the low byte
    ; enable receive and transmit, enable USART0 interrupts (UDR empty, Tx finished, Rx finished)
    LDI R16, (1<<RXEN0)|(0<<TXEN0)|(0<<UDRIE0)|(0<< TXCIE0)|(1<< RXCIE0)
    STS UCSR0B, R16 ;set control register UCSR0B with the corresponding bits
    ; configure USART 0 as asynchronous, set frame format: 8 data bits, 1 stop bit, no parity
    LDI R16, (0<<UMSEL00) |(1<<UCSZ01)|(1<< UCSZ00) |(0<< USBS0)|(0<<UPM01)|(0<< UPM00)
    STS UCSR0C, R16 ;set control register UCSR0C with the corresponding bits
    POP R16
    RET

USART0_reception_completed:
    PUSH R16 ;this handler routine will be automatically called every 61msec (in this example)
    IN R16, SREG ;Backup SREG. MANDATORY in interrupt handler routines
    PUSH R16
    push r20

    ;do the desired periodic task here
    LDS R16, UDR0  ;pick up the byte received and do anything with it
    cpi r16, 'a'
    brne sigue
    lds r20, valorPWM
    inc r20
    out ocr0a, r20
    sts valorPWM, r20
sigue:
    cpi r16, 's'
    brne termina
    lds r20, valorPWM
    dec r20
    out ocr0a, r20
    sts valorPWM, r20
    out ocr0a, r20

termina:
    pop r20
    POP R16
    OUT SREG, R16  ;Recover SREG from the previous backup
    POP R16
    RETI ;RETI is MANDATORY when returning from an interrupt handling routine