Assembly: UART

;**********************************************
;3/1/2019
;Transmitts strings of characters from uP to PC
;**********************************************
.include "ATxmega128A1Udef.inc"

.dseg
.org 0x2000
Outs:  .BYTE 3

.cseg
.org 0x0000
rjmp Main

Main:
ldi YL, low(Outs) ;input
ldi YH, high(Outs)
ldi XL, low(Outs) ;output
ldi XH, high(Outs)

ldi r16, 0xFF ;echo test
sts PORTC_DIR, r16
sts PORTC_OUT, r16

rcall USART_INIT ;setup USART
rcall IN_STRING
rcall OUT_STRING
LOOP:
rjmp LOOP

;******************************************
;This subroutine initializes the USART
;frame = 8 stop = 1 parity = odd
;baud = 115200 USART = PORT D
;******************************************
USART_INIT:
push r16 ;push reg used

ldi r16, 0x08 ;Rx out, rest in
sts PORTD_DIRSET, r16

ldi r16, 0x18 ;Tx and Rx enables
sts USARTD0_CTRLB, r16

ldi r16, 0x33 ;00 - async, 11 - odd
sts USARTD0_CTRLC, r16 ;0 - 1 stop, 011 - 8 bit

ldi r16, 0x0B ;lower BSEL = 11
sts USARTD0_BAUDCTRLA, r16

ldi r16, 0x90 ;BSCLAE = -7
sts USARTD0_BAUDCTRLB, r16 ;high BSEL = 0

pop r16
ret
;******************************************
;This subroutine takes in a string och
;characters
;******************************************
IN_STRING:
push r16 ;push reg used
STILL_GOING:
rcall IN_CHAR
st Y+, r16
cpi r16, 0x0D ;check if return
breq DONE

cpi r16, 0x08 ;check if backspace
brne STILL_GOING

ldi r16, 0x00 ;go back and store NULL
st -Y, r16
DONE:
pop r16
ret
;******************************************
;This subroutine outputs a string
;******************************************
OUT_STRING:
push r16 ;push reg used
AGAIN:
ld r16, X+
cpi r16, 0x00 ;check for end
    breq FINISHED
Rcall OUT_CHAR ;output char
rjmp AGAIN
FINISHED:
pop r16
ret

;******************************************
;This subroutine takes in a character
;******************************************
IN_CHAR:
push r17 ;push reg used
POLLING_IN:
lds r17, USARTD0_STATUS ;checking flag
andi r17, USART_RXCIF_bm ;bit7 mask
cpi r17, USART_RXCIF_bm
brne POLLING_IN ;no flag

lds r16, USARTD0_DATA ;testing echo
sts PORTC_OUT, r16

pop r17
ret
;******************************************
;This subroutine outputs one char
;******************************************
OUT_CHAR:
push r17 ;push reg used
POLLING_OUT:
lds r17, USARTD0_STATUS ;checking flag
andi r17, USART_DREIF_bm ;bit6 mask
cpi r17, USART_DREIF_bm
brne POLLING_OUT

sts USARTD0_DATA, r16 ;out char
pop r17
ret