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  0x00000200      ;Clock gate enable for port A
my_PORTA_PCR11 EQU  0x4004902C      ;PortA PCR 11 -> LED D7
my_PORTA_PCR28 EQU  0x40049070
my_PORTA_PCR29 EQU  0x40049074
PORTA_PCR_VAL EQU   0x00000140
my_GPIOA_PDOR EQU   0x400FF000
GPIOA_PDOR_VAL EQU  0x30000800
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 0x05F5E0FF
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 {9} of SIM_SCGC5, enable Port A clock gate
    LDR     r2, =my_SIM_SCGC5       ;0x40048038
    LDR     r1, =my_GPIOC_clken     ;0x00000200
    LDR     r3, [r2]
    ORR     r3, r3, r1
    STR     r3, [r2]                ;enable GPIO_PORTA

    LDR     r2, =my_PORTA_PCR11     ;0x4004902C address for orange LED
;For PortA PCR11, PCR28, PCR29 (3 LEDs):
;write 1 to bit {6}, DSE, high drive strength
;write 001 to bits {8-10}, MUX, alternative 1 GPIO
    LDR     r1, =PORTA_PCR_VAL      ;0x00000140
    STR     r1, [r2]                ;updates memory address to PTA28, yellow LED
    ldr     r2, =my_PORTA_PCR28
    STR     r1, [r2]                ;updates memory address to PTA29, green LED
    ldr     r2, =my_PORTA_PCR29
    STR     r1, [r2]
;turn off/reset LEDs:
;set PDOR PTA bits 11, 28, 29 to logic 1
    LDR     r2, =my_GPIOA_PDOR      ;0x4000FF000
    LDR     r1, =GPIOA_PDOR_VAL     ;0x300000800
    STR     r1, [r2], #20           ;updates memory addres to GPIOA_PDDR

;sets PDDR PTA fields 11, 28, 29 to general purpose output (1 to bits {11, 28, 29}
    STR     r1, [r2]

;Set PIT timer by writing 1 to bit {23}
    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
;2s/20ns - 1 =100e6 - 1 =0x05F5E0FF
    LDR      r1,=my_LDVAL1_value    ;0x05F5E0FF
    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]

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 to memory to clear flags
    LDR      r2, =irqcounter        ;load memory address of irqcounter
    LDRB     r3,[r2]                ;loads value from counter into r3
    CMP      r3,#1                  ;if 1 turn off leds
    BEQ      led_off
    ADD      r3,#1                  ;increment counter
    STRB     r3,[r2]                ;stores value of r3 into counter
    B        led_on                 ;if 0 turn on leds
led_off
    MOV      r3,#0x00               ;reset counter (limit between 0 and 1)
    str      r3, [r2]
    LDR      r7, =my_GPIOA_PSOR     ;memory address of PSOR
    LDR      r8, =GPIOA_PDOR_VAL    ;writes 1 at bits {11,28,29} to PSOR
    str      r8, [r7]               ;turns off LEDs
    POP      {pc}
led_on
    LDR      r7, =my_GPIOA_PCOR     ;memory address of PCOR
    LDR      r8, =GPIOA_PDOR_VAL    ;writes 1 at bits {11, 28, 29} to PCOR
    STR      r8, [r7]               ;turns on LEDs
    POP      {pc}                   ;restore program


    ALIGN
    AREA MyData, DATA, READWRITE
irqcounter DCD 0x00

DCD

    END