PRESERVE8
    AREA MyCode,CODE,READONLY
    EXPORT config
    IMPORT my_fprint
    EXPORT asm_pit1_irq
PIT1_IRQHandler EQU asm_pit1_irq+1
    EXPORT PIT1_IRQHandler      ;the vector table must contain odd addresses for the Cortex processor
my_SIM_SCGC5 EQU    0x40048038      ;Address for SIM_SCGC5
my_GPIOC_clken EQU  0x00000800      ;Clock gate enable for port A
my_PORTC_PCR0 EQU   0x4004B000
PORTC_PCR_VAL EQU   0x00000140
;my_GPIOA_PDOR EQU  0x400FF000
my_GPIOC_PDDR EQU   0x400FF094
my_GPIOC_PDOR EQU   0x400FF080
my_GPIOC_PCOR EQU   0x400FF088
my_GPIOC_PSOR EQU   0x400FF084
;GPIOA_PDOR_VAL EQU 0x30000800
GPIOC_PDDR_VAL EQU  0x000007FF
;my_GPIOA_PCOR EQU  0x400FF008
;my_GPIOA_PSOR EQU  0x400FF004
my_SIM_SCGC6 EQU    0x4004803C
my_SCGC6_value EQU  0x00800000

my_PIT_MCR EQU      0x40037000
my_PIT_LDVAL1 EQU   0x40037110
my_LDVAL1_value EQU 0x0000C34F
my_PIT_TFLG1 EQU    0x4003711C
my_PIT_TCTRL1 EQU   0x40037118

my_NVIC_addr EQU    0xE000E108
my_NVIC_value EQU   0x00000020
config

;write 1 to bit {11} of SIM_SCGC5, enable Port C clock gate
    LDR     r2, =my_SIM_SCGC5       ;0x40048038
    LDR     r1, =my_GPIOC_clken     ;0x00000800
    LDR     r3, [r2]
    ORR     r3, r3, r1
    STR     r3, [r2]                ;enable GPIO_PORTC

;For PortC PCR0-PCR10:
;write 1 to bit {6}, DSE, high drive strength
;write 001 to bits {8-10}, MUX, alternative 1 GPIO
    MOV     r4, #0
    LDR     r2, =my_PORTC_PCR0      ;0x4004B000 address PortC PCR0
    LDR     r1, =PORTC_PCR_VAL      ;0x00000140
next_portc
    STR r1,[r2], #4
    ADD r4,r4,#1
    CMP r4,#11
    BNE next_portc

;set PDDR PCR bits 0-10 to logic 1 - set them as outputs
;bits 0-10 set to 1 (= 0x07ff)
    LDR     r2, =my_GPIOC_PDDR      ;0x4000FF094
    LDR     r1, =GPIOC_PDDR_VAL     ;0x0000007FF
    STR     r1, [r2]

;initializing off at reset
    LDR r2, =my_GPIOC_PDOR
    LDR r5, =0x000000FF
    STR r5,[r2]

;Set PIT timer by writing 1 to bit {23} of SIM_SCGC6
    LDR      r2,=my_SIM_SCGC6       ;0x4004803C
    LDR      r1,=my_SCGC6_value     ;0x00800000
    LDR      r0,[r2]
    ORR      r0,r0,r1
    STR      r0,[r2]                ;enable clock to PIT1

;enable the PIT module (0 to bits {0-1} of the MCR)
    LDR      r2,=my_PIT_MCR         ;0x40037000, memory address for PCR
    MOV      r0,#0
    STR      r0,[r2]                ;stores 0x0 into PCR

;sets the timer to interrupt every 2s by writing LDVAL1
    LDR      r2,=my_PIT_LDVAL1      ;0x40037110, memory address for PIT_LDVAL1
;want it to trigger every 2s
;1ms/20ns - 1 =50e3 - 1 =0xC34F
    LDR      r1,=my_LDVAL1_value    ;0xC34F
    STR      r1,[r2]                ;load the count value to generate interrupt periodically

;store 1 in bits {0,1} of TCTRL1, enable timer and interrupts
    LDR      r2,=my_PIT_TCTRL1      ;0x40037118, memory address for PIT_TCTRL1
    MOV      r0,#0x3
    STR      r0,[r2]                ;set TIE and TEN bits

;NVIC CONVIG
    LDR      r2,=my_NVIC_value      ;0x00000020 sets IRQ 69
    LDR      r1,=my_NVIC_addr       ;0xE000E108
    STR      r2, [r1]


    LDR      r5, =value             ;loads address of value for 7seg


loop B loop

asm_pit1_irq
    PUSH     {lr}                   ;store LR
    LDR      r2,=my_PIT_TFLG1       ;load memory address of TFLG1
    MOV      r3,#0x01               ;1 to clear flag
    STR      r3,[r2]                ;store 1 to the memory to clear flags
    LDR      r2, =irqcounter        ;load memory address of counter
    LDRB     r3,[r2]                ;loads value from counter into r3
    B        sevSeg

sevSeg
    LDR      r7, =sevSegTable       ;loads address of lookup table
    LDR      r6, [r5], #4           ;loads first value to be printed
    LSL      r6, r6, #2             ;multiply value by 4
    ADD      r6, r6, r7             ;add shift value to memory address
    LDR      r8, [r6]               ;load value from lookup table
    LDR      R9, =my_GPIOC_PDOR     ;load PDOR address to output
    CMP      r3, #1                 ;branch to correct digit #
    BEQ      dig_one
    BGT      dig_two

dig_zero
    ADD      r3,#1                  ;increment counter
    STRB     r3,[r2]                ;updating counter in memory
    add      r8, r8, #0x400         ;0x400 turns on MS digit PTC10
    ldr      r11, [r5]              ;check if next value is period
    cmp      r11, #0x2E             ;print to 7seg and update address if true
    subeq    r8, r8, #0x80
    addeq    r5, r5, #4
    str      r8, [r9]               ;store value in PDOR
    pop      {pc}                   ;restore program

dig_one
    ADD      r3,#1                  ;increment counter
    STRB     r3,[r2]                ;updating counter in memory
    add      r8, r8, #0x200         ;0x200 turns on middle digit PTC9
    ldr      r11, [r5]              ;check if next value is period
    cmp      r11, #0x2E             ;print to 7seg and update address if true
    subeq    r8, r8, #0x80
    addeq    r5, r5, #4
    str      r8, [r9]               ;store value in PDOR
    POP      {pc}                   ;restore program
dig_two
    mov      r3, #0x0               ;reset counter (limit between 0 and 2)
    strb     r3, [r2]               ;store 0 in counter memory
    add      r8, r8, #0x100         ;0x100 turns on LS digit PTC8
    ldr      r11, [r5]              ;check if next value is period
    cmp      r11, #0x2E             ;print to 7seg and update address if true
    subeq    r8, r8, #0x80
    addeq    r5, r5, #4
    STR      r8, [r9]               ;store value in PDOR
    LDR      r5, =value             ;restart from first digit
    POP      {pc}                   ;restore program


    ALIGN
    AREA MyData, DATA, READWRITE
irqcounter  DCD 0x00
value       DCD 0x07
            dcd 0x2E
            DCD 0x01
            DCD 0x2E
            DCD 0x02
            dcd 0x2e
sevSegTable DCD 0xC0
            DCD 0xF9
            DCD 0xA4
            DCD 0xB0
            DCD 0x99
            DCD 0x92
            DCD 0x82
            DCD 0xF8
            DCD 0x98
            DCD 0xFF    ;period



DCD

    END