SECTION "main", ROM0[$db01]

_start:
    ld d,h
    ld e,l
writeagain:
    push de
    ld hl,$fff8
    add hl,de
    ld d,h
    ld e,l
.testkeys
    ldh a,[$fff8]
    and a
    jr nz,.testkeys
    ld hl,$c3a0
write:
    ld [hl],$7c
    inc hl
    ld a,d
    call writehex
    ld a,e
    call writehex
    ld [hl],$e3
    inc hl
    ld a,[de]
    call writehex
    ld [hl],$7c
    ld bc,12
    add hl,bc
    inc de
    ld a,l
    cp 8
    jr nz,write
waiting:
    ld hl,$c445
    ld [hl],$ed
    pop de
.testbuttons
    db $76 ; halt
    ldh a,[$fff8]
    ld b,a
    bit 3,b
    jr z,.nostartbtn
    ld a,d
    add $10
    ld d,a
.nostartbtn
    bit 2,b
    jr z,.noselectbtn
    inc d
.noselectbtn
    bit 1,b
    ret nz
    bit 0,b
    jr nz,bytechangeloop
    bit 6,b
    jr z,.noupbtn
    dec de
.noupbtn
    bit 7,b
    jr z,.nodownbtn
    inc de
.nodownbtn
    bit 5,b
    jr z,.noleftbtn
    ld hl,$fff0
    add hl,de
    ld d,h
    ld e,l
.noleftbtn
    bit 4,b
    jr z,.norightbtn
    ld hl,$0010
    add hl,de
    ld d,h
    ld e,l
.norightbtn
writeagainbounce:
    jr writeagain
    
storeandwriteagain:
    ld a,c
    ld [de],a
    jr writeagainbounce
    
bytechangeloop:
    ld [hl],$ec
    ld a,[de]
    ld c,a
bytechangeloopentry:
    db $76 ; halt
    ldh a,[$fff8]
    and a
    jr z,storeandwriteagain
    ld b,a
    bit 6,b
    jr z,.noupbtn
    ld a,c
    add $10
    ld c,a
.noupbtn
    bit 7,b
    jr z,.nodownbtn
    ld a,c
    sub $10
    ld c,a
.nodownbtn
    bit 5,b
    jr z,.noleftbtn
    dec c
.noleftbtn
    bit 4,b
    jr z,.norightbtn
    inc c
.norightbtn
    ld l,$46
    ld a,c
    call writehex
.waitbuttonsc
    ldh a,[$fff8]
    cp $0d
    jr z,specialexec
    and $fe
    jr nz,.waitbuttonsc
    jr bytechangeloopentry

writehex:
    ld b,a
    swap a
    and $0f
    call writehexdigit
    ld a,b
    ; fall through to writehexdigit

writehexdigit:
    and $0f
    add $f6
    jr nc,.noadd
    add $60
.noadd
    ld [hli],a
.retinstr
    ret

specialexec:
    ld hl,.executive
    ld [hl],e
    inc hl
    ld [hl],d
    call $3e94 ; GetPredefRegisters
    ld a,[$cc4e]
    db $c3 ; jp
.executive
    ; subroutine address goes here