.export _main
 .include "atari.inc"

 sptr   = FR0
 scount = FR0+2

 .ifndef start_addr
 start_addr = $4000
 .endif

 .ifndef RAW
 .org start_addr - 6
 .word $ffff
 .word start_addr
 .word end_addr - 1
 .endif

 .org start_addr
print_addr:
 jsr pa
pa:         ; pull return address, print it (don't put it back on the stack)
 pla
 sec
 sbc #2     ; pa-1 was pushed, we want to print print_addr
 sta sptr   ; lo byte
 pla
 sbc #0
 sta sptr+1
 jsr printhex
 lda sptr
 jmp printhex
 rts

_main:
 ldx #1
 stx CRSINH
 lda #<str1
 ldx #>str1
 jsr printstr
 lda #' '
 jsr printa
 lda #<str2
 ldx #>str2
 jsr printstr
 lda #'.'
 jsr printa
 lda #EOL
 jsr printa
 lda #<addr_str
 ldx #>addr_str
 jsr printstr
 jsr print_addr
 lda #EOL
 jsr printa
 lda #<end_str
 ldx #>end_str
 jsr printstr
 lda #>(end_addr-1)
 jsr printhex
 lda #<(end_addr-1)
 jsr printhex
 lda #<memlo_str
 ldx #>memlo_str
 jsr printstr
 lda MEMLO+1
 jsr printhex
 lda MEMLO
 jsr printhex
 lda #<relax_str
 ldx #>relax_str
 jsr printstr
 jsr junksub

cycle:
 lda RTCLOK+2
 and #$f0
 ora #$06
 sta COLOR2
 jmp cycle

printstr:
 sta sptr
 stx sptr+1
 lda #0
 sta scount
strloop:
 ldy scount
 lda (sptr),y
 bne printchr
 rts
printchr:
 jsr printa
 inc scount
 bne strloop
 rts

 ; Subroutine: Print A register in hex.
printhex:
 pha           ; stash argument
 lsr           ; shift right 4 times,
 lsr           ;   to get the first hex digit
 lsr           ;   (aka nybble) into the bottom
 lsr           ;    4 bit positions.
 jsr printxdig ; print the top nybble.
 pla           ; restore original value...
 and #$0f      ; mask off high nybble
 ; fall through to print the 2nd digit.

 ; Subroutine: Print a nybble (A=0 to $0f) in hex.
printxdig:
 ora #$30 ; 0-9 now ASCII...
 cmp #$3a ; do we have A-F?
 bcc xok  ; if not, don't adjust it
 adc #$26 ; A-F now ASCII: $3a + $26 + 1 (carry always set) = $61 (a)
xok:
 ; fall through to print the digit.

 ; Subroutine: Print ATASCII character in A.
 ; Assumes IOCB #0 is opened on the E: device, which is how the
 ; Atari boots up. Uses "call-by-RTS" (weird looking but standard).
printa:
 tax
 lda ICPTH ; the print-one-byte vector for IOCB 0.
 pha
 lda ICPTL ; low byte of vector
 pha
 txa
 rts

junksub:
 .repeat 512
 nop
 .endrep
 lda #'O'
 jsr printa
 lda #'K'
 jmp printa

str1:      .byte "Hello",0
str2:      .byte "World",0
addr_str:  .byte EOL, "I am currently located at $",0
end_str:   .byte      "My code ends at           $",0
memlo_str: .byte EOL, "MEMLO is currently set to $",0
relax_str: .byte EOL, EOL, "Watchen das blinkenlights...",EOL,0

 .ifndef RAW
end_addr:
 .word INITAD
 .word INITAD+1
 .word _main
 .endif