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.data

        data 0x0A

        data 0x0D

buffer:

.text

;;; initialization

        ldib    r0, -8          ; config/status

        ldib    r1, -6          ; data

        ldil    r2,  lo(buffer) ; buffer address

        ldih    r2,  hi(buffer) ; buffer address

        ldib    r3,  0x0A       ; newline character

        ldib    r4,  0x0D       ; carriage return

        ldib    r5,  0           ; mode

        ldib    r7,  isr        ; register isr

        stvec   r7,  3

        ldib    r7, (1 << 3)    ; enable receive interrupts

        store   r7,  r0

        sei                     ; enable interrupts

;;; loop forever

loop:   br loop

;;; ISR

isr:

        cmpi    r5, 0            ; check mode

        brnz    write_mode

;;; reading

read_mode:

        load    r7, r1          ; read data

        cmp     r7, r3          ; change mode upon newline

        brnz    read_CR

        ldib    r7, (1 << 2)    ; do the change

        store   r7, r0

        ldib    r5, 1

        reti

read_CR:

        cmp     r7, r4          ; ignore carriage return

        brnz    read_cont

        reti

read_cont:

        storel  r7, r2          ; store date

        addi    r2,  1

        reti

;;; writing

write_mode:

        addi    r2, -1

        cmpi    r2, -1          ; change mode if there is no more data

        brnz    write_cont

        ldil    r2,  lo(buffer) ; correct pointer to buffer

        ldih    r2,  hi(buffer)

        ldib    r7, (1 << 3)    ; do the change

        store   r7, r0

        ldib    r5, 0

        reti

write_cont:

        loadl   r7, r2          ; write data

        store   r7, r1

        reti