cc65/libsrc/atari7800/mono_cputc.s

;
; Mark Keates, Christian Groessler, Piotr Fusik, Karri Kaksonen
;
; void cputcxy (unsigned char x, unsigned char y, char c);
; void cputc (char c);
;

        .export         _mono_cputc
        .import         mono_gotox, mono_gotoy, pusha0
        .import         pushax
        .import         _mono_screen

        .include        "atari7800.inc"
        .include        "extzp.inc"

        .code

;---------------------------------------------------------------------------
; 8x16 routine

umula0:
        ldy     #8                 ; Number of bits
        lda     #0
        lsr     ptr7800            ; Get first bit into carry
@L0:    bcc     @L1

        clc
        adc     ptrtmp
        tax
        lda     ptrtmp+1           ; hi byte of left op
        clc
        adc     ptr7800+1
        sta     ptr7800+1
        txa

@L1:    ror     ptr7800+1
        ror     a
        ror     ptr7800
        dey
        bne     @L0
        tax
        lda     ptr7800            ; Load the result
        rts

;-----------------------------------------------------------------------------
; Put a character on screen
;
; The code will handle newlines that wrap to start of screen
;
        .proc   _mono_cputc

        cmp     #$0A            ; LF
        bne     @L4
@L1:    lda     #0              ; newline
        jsr     mono_gotox
        lda     CURS_Y
        cmp     #(screenrows-1)
        bne     @L2
        lda     #0
        beq     @L3
@L2:    clc
        adc     #1
@L3:    jmp     mono_gotoy

@L4:
        pha

        lda     #0
        sta     ptr7800+1
        sta     ptrtmp+1
        lda     CURS_Y          ; Find position on screen buffer
        sta     ptr7800
        lda     #mono_charsperline
        sta     ptrtmp
        jsr     umula0
        clc
        adc     CURS_X
        bcc     @L11
        inx
@L11:   clc
        adc     #<(_mono_screen)
        sta     ptr7800
        bcc     @L12
        inx
@L12:   txa
        clc
        adc     #>(_mono_screen)
        sta     ptr7800+1

        pla                     ; Print character on screen
        ldy     #0
        sta     (ptr7800),y

        lda     CURS_X          ; Increment cursor
        cmp     #(mono_charsperline-1)
        beq     @L1
        clc
        adc     #1
        jmp     mono_gotox

        .endproc