AVR UART handling basic test plain assembler

; Should be the same as previous, but for now it's plain assembler compiled with avra
; The result is slightly different, now it's well seen that stackpointer is overwritten
; At the start it's trasnmit '\' = 0x5C but when I start transmit from the PC side
; quickly changed to something different, after a while even go into the trap for
; unused interrupts - at the start I'm disble interrupts globally.
;
;* *********************************************************************
;* avr-uart-test.asm
;* AVR uart handler for ATmega16
;* Plain assembler using avra
;* by tovis 2015
;* avra avr-uart-test.asm -l avr-uart-test.lst
;***********************************************************************
.INCLUDE "rg_m16def.inc"

;***********************************************************************
.ORG    0x0000
        JMP     START0                  ; RESET
        JMP     ISR_TRAP                ; INT0
        JMP     ISR_TRAP                ; INT1
        JMP     ISR_TRAP                ; TIMER2_COMPARE
        JMP     ISR_TRAP                ; TIMER2_OVERFLOW
        JMP     ISR_TRAP                ; TIMER1_CAPTURE
        JMP     ISR_TRAP                ; TIMER1_COMPARE_A
        JMP     ISR_TRAP                ; TIMER1_COMPARE_B
        JMP     ISR_TRAP                ; TIMER1_OVERFLOW
        JMP     ISR_TRAP                ; TIMER0_OVERFLOW
        JMP     ISR_TRAP                ; SPI_TRASNFER_COMPLETE
        JMP     ISR_TRAP                ; USART_RX_COMPLETE
        JMP     ISR_TRAP                ; USART_TX_COMPLETE
        JMP     ISR_TRAP                ; ADC_CONVERSION_COMPLETE
        JMP     ISR_TRAP                ; EEPROM_READY
        JMP     ISR_TRAP                ; ANALOG_COMPARATOR
        JMP     ISR_TRAP                ; TWI_INTERFACE
        JMP     ISR_TRAP                ; INT2
        JMP     ISR_TRAP                ; TIMER0_COMPARE_MATCH
        JMP     ISR_TRAP                ; STORE_PROGRAM_MEMORY_READY

ISR_TRAP:
        CALL    toggle_A7
        RJMP    ISR_TRAP

;***********************************************************************
.ORG    0x0100
START0:
        CLR     R16                     ; Clear R16
        OUT     SREG, R16               ; Disable interrupt
        LDI     R16, LOW(RAMEND)        ; Stack pouinter to RAMEND = 0x045F
        OUT     SPL, R16
        ; ??? LDI     R16, HIGH(RAMEND)
        LDI     R16, 0x02
        OUT     SPH, R16
;-------
        SER     R16
        OUT     DDRA, R16               ; PORTA all pins are output
        CALL    uart_setup
        ; ??? SEI                             ; Global interrupt enable
main_loop:
        CALL    uart_get
        CALL    uart_put
        CALL    toggle_A0
        RJMP    main_loop
;***********************************************************************
uart_get:
        SBIS    UCSRA,RXC               ; check if received data available
        RJMP    uart_get_notready
        CALL    toggle_A2               ; ???
        PUSH    R16
        IN      R16, UDR                ; read data from receiver buffer
        POP     R16
uart_get_notready:
        RET
;-----------------------------------------------------------------------
uart_put:
        SBIS    UCSRA, UDRE             ; check if UDR is empty
        RJMP    uart_put_notready
        CALL    toggle_A1               ; ???
        ; LDI     R16, 'o'
        IN      R16, SPL
        OUT     UDR, R16
uart_put_notready:
        RET
;-----------------------------------------------------------------------
uart_setup:
        EOR     R16, R16                ; Clear R16
        OUT     UCSRB, R16              ; Disable USART interrupts
                                        ; Disable receive/transmit
                                        ; and UCSZ2 = 0 for 8 bit data
        LDI     R16, LOW(103)           ; Setup Baud rate 9600
        OUT     UBRRL, R16
        LDI     R16, HIGH(103)
        ANDI    R16, 0x7F               ; URSEL = 0 - access UBRRH
        OUT     UBRRH, R16

        OUT     UCSRA, R16              ; Clrear status and U2X, MPCM
        LDI     R16, 0b10000110         ; Asynchronous 8n1 and URSEL = 1
        OUT     UCSRC, R16              ; Set ssynchronous 8n1
        ;---
        SBI     UCSRB, TXEN             ; Transmitter enable
        SBI     UCSRB, RXEN             ; Receiver enable
        RET
;***********************************************************************
toggle_A0:
        IN      R16, PORTA
        LDI     R17, 0x01
        EOR     R16, R17
        OUT     PORTA, R16
        RET
;-----------------------------------------------------------------------
toggle_A1:
        IN      R16, PORTA
        LDI     R17, 0x02
        EOR     R16, R17
        OUT     PORTA, R16
        RET
;-----------------------------------------------------------------------
toggle_A2:
        IN      R16, PORTA
        LDI     R17, 0x04
        EOR     R16, R17
        OUT     PORTA, R16
        RET
;-----------------------------------------------------------------------
toggle_A3:
        IN      R16, PORTA
        LDI     R17, 0x08
        EOR     R16, R17
        OUT     PORTA, R16
        RET
;-----------------------------------------------------------------------
toggle_A7:
        IN      R16, PORTA
        LDI     R17, 0x80
        EOR     R16, R17
        OUT     PORTA, R16
        RET
;/***********************************************************************
;* avr-uart-test.asm
; **********************************************************************/