.include "bios.inc"

.area   TAPELOAD (ABS)
.org    TAPE_LOADER_ROM_ADDRESS

TAPE_PORT       = 0x18
MAX_BLOCK_SIZE  = 0x100

STACK_TOP       = 0xBFFF
WORK_BASE       = 0xB000

OLD_SP          = WORK_BASE + 0x00 ; word
OLD_IFF         = WORK_BASE + 0x02 ; byte

BLOCK_BUFFER    = WORK_BASE + 0x100 ; MAX_BLOCK_SIZE

; #################################################3
; Entry
; #################################################3
tape_loader:
    ld      (OLD_SP),sp
    ; Save interrupt state.
    ld      a,i
    jp      po,iff_was_off
    ld      a,#1
    jr      save_iff
iff_was_off:
    xor     a
save_iff:
    ld      (OLD_IFF),a
    di
    ld      sp,#STACK_TOP

main:
    ; Initial message.
    ld      hl,#msg_start
    call    print_string_ei

; #################################################3
; Exit
; #################################################3
exit:
    ei
    call    BIOS_FLUSH
    di
    ld      sp,(OLD_SP)
    ; Return code 0
    ld      a,#0
    ld      c,a
    ; Restore caller's interrupt state.
    ld      a,(OLD_IFF)
    or      a
    ld      a,c
    jr      z,return_di
    ei      
    ret
return_di:
    ret

; #################################################3
; IO Helper functions
; #################################################3
print_string_ei:
    ei
    call    print_string
    call	BIOS_FLUSH
    di
    ret

print_string:
    ld      a,(hl)
    or      a
    ret     z
    call    BIOS_PUTC
    inc     hl
    jr      print_string

print_crlf:
    ld      a,#13
    call    BIOS_PUTC
    ld      a,#10
    jp      BIOS_PUTC

print_hex16:
    push	hl
    ld	a,h
    call	print_hex8
    pop	hl
    ld	a,l
    call	print_hex8
    ret

print_hex8:
    push    af
    rrca
    rrca
    rrca
    rrca
    and     #0x0F
    call    print_hex_nibble
    pop     af
    and     #0x0F

    ; fall through
print_hex_nibble:
    cp      #10
    jr      c,print_hex_digit
    add     a,#('A' - 10)
    jp      BIOS_PUTC

print_hex_digit:
    add     a,#'0'
    jp      BIOS_PUTC

; #################################################3
; Strings
; #################################################3
msg_start:
    .ascii  "TAPE DECODE TEST - PLAY TAPE"
    .db     13,10,0