GPIO_PORTF_DIR_R   EQU 0x40025400
GPIO_PORTF_DEN_R   EQU 0x4002551C
GPIO_PORTF_DATA_R EQU 0x400253FC
SYSCTL_RCGCGPIO_R  EQU 0x400FE608

    AREA    |.text|, CODE, READONLY, ALIGN=2
    THUMB
    EXPORT   GPIOF_INIT

GPIOF_INIT
    LDR R1, =SYSCTL_RCGCGPIO_R      ; R1 = &SYSCTL_RCGCGPIO_R
    LDR R0, [R1]                    ; R0 = [R1]
    ORR R0, R0, #0x20               ; Port F
    STR R0, [R1]                    ; [R1] = R0
    NOP
    NOP                             ; allow time to finish activating
    ; set direction register
    LDR R1, =GPIO_PORTF_DIR_R       ; R1 = &GPIO_PORTF_DIR_R
    LDR R0, [R1]                    ; R0 = [R1]
    ORR R0, R0, #0x04               ; R0 = R0|0x04 (make PF2 output; PF2 built-in blue LED)
    STR R0, [R1]                    ; [R1] = R0

    ; enable digital port
    LDR R1, =GPIO_PORTF_DEN_R       ; R1 = &GPIO_PORTF_DEN_R
    LDR R0, [R1]                    ; R0 = [R1]
    ORR R0, R0, #0x04               ; R0 = R0|0x04 (enable digital I/O on PF2)
    STR R0, [R1]                    ; [R1] = R0

    BX LR

    ALIGN                           ; make sure the end of this section is aligned
    END                             ; end of file