fake_cpm.sz8

CONSOLE_PORT equ 0
STATUS_PORT  equ 1
EXIT_PORT    equ 2
	org $E400
	jp handle_call
	ld a, (should_exit)
	dec a
	jr z, do_exit
	ld a, 1
	ld (should_exit), a
	jp $100
do_exit:
no_impl
	out (EXIT_PORT), a
should_exit:
	dc.b 0
	
console_in:
	in a, (CONSOLE_PORT)
	ld l, a
	ret
console_out:
	ld a, e
	out (CONSOLE_PORT), a
	ret
get_iobyte:
	ld a, (3)
	ld l, a
	ret
set_iobyte:
	ld a, e
	ld (3), a
	ret
write_string:
	ld c, '$'
	jp .start
.continue
	out (CONSOLE_PORT), a
	inc de
.start
	ld a, (de)
	cp c
	jr nz, .continue
	;flush output
	out (STATUS_PORT),a 
	ret
read_string:
	ld a, (de)
	ld c, a
	ld b, $A ;newline
	inc c
	inc de
	push de
	inc de
	jp .start
.continue
	in a, (CONSOLE_PORT)
	cp b
	jr z, .end
	ld (de), a
	inc de
.start
	dec c
	jr nz, .continue
	;todo: consume excess characters
.end
	pop hl
	ex de, hl
	sbc hl, de
	ld a, l
	ld (de), a
	ret

console_status:
	in a, (STATUS_PORT)
	ld l, a
	ret

handle_call:
	ld a, c
	or a
	jr z, do_exit
	dec a
	jr z, console_in
	dec a
	jr z, console_out
	dec a
	jr z, no_impl ;aux reader input
	dec a
	jr z, no_impl ;aux punch output
	dec a
	jr z, no_impl ;printer output
	dec a
	jr z, no_impl ;direct console IO
	dec a
	jr z, get_iobyte
	dec a
	jr z, set_iobyte
	dec a
	jr z, write_string
	dec a
	jr z, read_string
	dec a
	jr z, console_status
	jp no_impl