;### MACROS & defs (.equ)###

; Macro LOAD_CONST loads given registers with immediate value, example: LOAD_CONST  R16,R17 1234
.MACRO LOAD_CONST
    LDI @0, LOW(@2)
    LDI @1, HIGH (@2)
.ENDMACRO

/*** Display ***/
.equ DigitsPort = PORTB
.equ SegmentsPort = PORTD
.equ DisplayRefreshPeriod = 5 ; W MS

; SET_DIGIT diplay digit of a number given in macro argument, example: SET_DIGIT 2
.MACRO SET_DIGIT

    PUSH R16
    PUSH R17

    LDI R16, (0b0001_0000>>@0)
    OUT PORTB, R16
    MOV R16, Dig_@0
    RCALL DigitTo7segCode
    LOAD_CONST R16,R17,DisplayRefreshPeriod
    RCALL DealyInMs

    POP R17
    POP R16

.ENDMACRO

; ### GLOBAL VARIABLES ###

.def PulseEdgeCtrL=R0
.def PulseEdgeCtrH=R1

.def Dig_0=R2
.def Dig_1=R3
.def Dig_2=R4
.def Dig_3=R5

; ### INTERRUPT VECTORS ###
.cseg

.org     0      rjmp    _main
.org OC1Aaddr   rjmp  _Timer_ISR
.org PCIBaddr   rjmp  _ExtInt_ISR

; ### INTERRUPT SEERVICE ROUTINES ###

_ExtInt_ISR:

    PUSH R16
    IN R16, SREG
    PUSH R16
    PUSH R24
    PUSH R25

    MOVW R25:R24, PulseEdgeCtrH:PulseEdgeCtrl
    ADIW R25:R24, 1
    MOVW PulseEdgeCtrH:PulseEdgeCtrl, R25:R24

    POP R25
    POP R24
    POP R16
    OUT SREG, R16
    POP R16

reti

_Timer_ISR:

    PUSH R16
    IN R16, SREG
    PUSH R16
    push R17
    push R18
    push R19

    MOVW R17:R16, PulseEdgeCtrH:PulseEdgeCtrl
    LSR R17
    ROR R16

    CLR PulseEdgeCtrH
    CLR PulseEdgeCtrl

    MOV Dig_0, R16
    MOV Dig_0, R17
    MOV Dig_0, R18
    MOV Dig_0, R19

    pop R19
    pop R18
    pop R17
    POP R16
    OUT SREG, R16
    POP R16

  reti

; ### MAIN PROGAM ###

_main:
    ; *** Initialisations ***

    ;--- Ext. ints --- PB0
    LDI R18, 0b0010_0000
    OUT GIMSK, R18
    LDI R18, 0b0000_0001
    OUT PCMSK0, R18

    ;--- Timer1 --- CTC with 256 prescaller
    LDI R16, 0
    OUT TCCR1A, R16
    LDI R16, 0b0000_1100
    OUT TCCR1B, R16
    LOAD_CONST R16, R17, 31249
    OUT OCR1AH, R16
    OUT OCR1AL, R17
    LDI R16,0b0100_0000
    OUT TIMSK, R16

    ;---  Display  ---
    LDI R18, 0b0001_1110
    OUT DDRB, R18
    LDI R18, 0b0111_1111
    OUT DDRD, R18

    ; --- enable gloabl interrupts
    SEI

MainLoop:   ; presents Digit0-3 variables on a Display
            SET_DIGIT 0
            SET_DIGIT 1
            SET_DIGIT 2
            SET_DIGIT 3

            RJMP MainLoop

; ### SUBROUTINES ###

;*** NumberToDigits ***
;converts number to coresponding digits
;input/otput: R16-17/R16-19
;internals: X_R,Y_R,Q_R,R_R - see _Divider

; internals
.def Dig0=R22 ; Digits temps
.def Dig1=R23 ;
.def Dig2=R24 ;
.def Dig3=R25 ;

_NumberToDigits:

    push Dig0
    push Dig1
    push Dig2
    push Dig3
    PUSH R17
    PUSH R16

    ; thousands
    LOAD_CONST R16,R17,1000
    RCALL _Divide
    MOV Dig3, QL

    ; hundreads
    LOAD_CONST R16,R17,100
    RCALL _Divide
    MOV Dig2, QL

    ; tens
    LOAD_CONST R16,R17,10
    RCALL _Divide
    MOV Dig1, QL

    ; ones
    MOV Dig0, RL

    ; otput result
    mov R16,Dig0
    mov R17,Dig1
    mov R18,Dig2
    mov R19,Dig3

    POP R16
    POP R17
    pop Dig3
    pop Dig2
    pop Dig1
    pop Dig0

    ret

;*** Divide ***
; divide 16-bit nr by 16-bit nr; X/Y -> Qotient,Reminder
; Input/Output: R16-19, Internal R24-25

; inputs
.def XL=R16 ; divident
.def XH=R17

.def YL=R18 ; divider
.def YH=R19

; outputs

.def RL=R16 ; reminder
.def RH=R17

.def QL=R18 ; quotient
.def QH=R19

; internal
.def QCtrL=R24
.def QCtrH=R25

_Divide:

        push R24 ;save internal variables on stack
        push R25

        CLR QCtrH
        CLR QCtrL
        CP XH, YH
        CPC XL, YL
        BRLO DIEND

        DIELOOP:
            SUB XH, YH
            SBC XL, YL
            ADIW QCtrH:QCtrL, 1
            CP XH, YH
            CPC XL, YL
            BRSH DIELOOP

        DIEND:

        MOVW QH:QL, QCtrH:QCtrL

        pop R25 ; pop internal variables from stack
        pop R24

        ret

; *** DigitTo7segCode ***
; In/Out - R16

Table: .db 0x3f,0x06,0x5B,0x4F,0x66,0x6d,0x7D,0x07,0xff,0x6f

DigitTo7segCode:

push R30
push R31

LDI R30, LOW(Table<<1)
LDI R31, HIGH(Table<<1)

ADD R30,R16
CLR R16
ADC R31,R16

LPM R16, Z

pop R31
pop R30

ret

; *** DelayInMs ***
; In: R16,R17
DealyInMs:
            push R24
            push R25

            MOVW R25:R24, R17:R16

            DELOOP:
                RCALL OneMsLoop
                SBIW R25:R24, 1
                BRBC 1, DELOOP

            pop R25
            pop R24

            ret

; *** OneMsLoop ***
OneMsLoop:
            push R24
            push R25

            LOAD_CONST R24,R25,2000

L1:         SBIW R24:R25,1
            BRNE L1

            pop R25
            pop R24

            ret