Game 2Unit 18 of 191 hr learning time
A Theme in One Voice
Write music on one bit. Turn the note-table into a tune the title loops while it waits — pitch/duration pairs driving the beep primitive — and compose a short, solemn theme in D minor. One voice, no harmony: the melody carries the whole mood alone, and the keypress is never swallowed.
95% of Shadowkeep
The keep is a complete game, and it is heard as you move through it now — footfalls, doors. But its title opens in silence, waiting mutely for you to press SPACE. A game announces itself; it has a theme, the few seconds of music that tell you what you’re about to play. You have written one before — the dusk bells that tolled over The Long Night’s title, note and keyboard-poll interleaved so a waiting keypress was never swallowed. The keep deserves its own, on the same instrument: the single-bit beeper you clicked footsteps with in Unit 17, asked now to carry not a footstep but a tune — and looping it under the title, holding to that same discipline a title tune owes the player.
What you’ll hear by the end
The title screen is unchanged to look at — but now a short, solemn phrase plays under it, and loops, while the keep waits for you. Press SPACE at any moment and it breaks off cleanly and the game begins. The keep introduces itself before you take a step.
A note is a stack of beeps
One beep runs at most 255 cycles — too short for a note you can hold. So play_note stacks beeps in chunks: a note’s duration is a count of fixed-size chunks, and the routine runs the tone chunk after chunk until the count runs out:
play_note: ; C = pitch, D = duration in chunks
.pn_loop:
ld b, 24 ; one chunk = 24 square-wave cycles
push de
call beep ; B cycles at pitch C
pop de
dec d
jr nz, .pn_loop
retStack a handful of chunks and a note breathes for a third of a second; a couple and it’s a quick passing tone. Duration becomes rhythm. A rest_chunks of matched silence gives the rests their weight.
Composing for one voice
The hard part isn’t the code — it’s that the beeper is monophonic. One bit, one note at a time: no chords, no bass under the melody, no harmony to hide behind. The tune has to carry rhythm, mood and identity entirely on its own line. So we write a small, deliberate phrase in D minor — dark, solemn, the keep before the dark:
theme:
defb 75, 8 ; D5
defb 63, 8 ; F5
defb 50, 8 ; A5
defb 50, 12 ; A5 (held)
defb 56, 8 ; G5
defb 63, 8 ; F5
defb 66, 8 ; E5
defb 75, 16 ; D5 (resolve)
defb 0, 6 ; a breath (pitch 0 = rest)
; ... a short answer, then home ...
defb $FF ; endIt rises through the D-minor triad to a held A, then steps back down and resolves home to D — a shape you can hum, which is the whole job of a theme.
Looping without swallowing the keypress
Here is the discipline The Long Night taught, applied again. The title doesn’t play the theme and then wait for SPACE — it would swallow a press that came during the music. Instead the wait-loop is the player: it walks the theme note by note, and between every note it checks the keyboard. Reach $FF and it loops back to the start; press SPACE and it breaks out at once:
.tt_note:
; check SPACE — pressed? leave immediately
; read the next (pitch, duration) from the theme
; $FF? loop back to the top of the theme
; play the note (or rest), then round againSo the theme loops for as long as you leave the title up, and your keypress is caught the instant it lands — never held hostage by a note in progress.
Milestone — give the keep a theme
play_note stacks the beeper in chunks so a note can breathe; the theme is a short
D-minor phrase, one voice carrying the whole mood. The title’s wait-loop doubles as
the player: it walks the theme note by note, checks SPACE between each, loops at the
end, and breaks the instant you press — the interleave that never swallows a keypress.
di/ei hand the CPU wholly to the music while the title waits, then back to the loop.
Step 1: a note player, a D-minor theme, and a title that loops it
+78-6
| 1 | 1 | ; Shadowkeep — Unit 18: A Theme in One Voice | |
| 2 | 2 | ; Cumulative build; every step runs on its own. Narrative: the unit page. | |
| 3 | - | ; step-00 = Unit 17's end: the keep sounds, but the title waits in silence. | |
| 3 | + | ; step-01 gives the title a voice — a solemn D-minor phrase, looping as it waits. | |
| 4 | 4 | | |
| 5 | 5 | org 32768 | |
| 6 | 6 | | |
| ... | |||
| 804 | 804 | ld a, c | |
| 805 | 805 | cp 130 ; until it has groaned down low | |
| 806 | 806 | jr c, .sd_sweep | |
| 807 | + | ret | |
| 808 | + | | |
| 809 | + | ; ---------------------------------------------------------------------------- | |
| 810 | + | ; The music player — a note-table interpreter for the title theme. | |
| 811 | + | ; play_note — C = pitch (beep delay), D = duration in chunks. A note is the beep | |
| 812 | + | ; primitive run for D fixed-size chunks, so a note can be long though one beep's | |
| 813 | + | ; cycle count is a single byte. | |
| 814 | + | ; ---------------------------------------------------------------------------- | |
| 815 | + | play_note: | |
| 816 | + | .pn_loop: | |
| 817 | + | ld b, 24 ; one chunk = 24 square-wave cycles | |
| 818 | + | push de | |
| 819 | + | call beep ; B cycles at pitch C | |
| 820 | + | pop de | |
| 821 | + | dec d | |
| 822 | + | jr nz, .pn_loop | |
| 823 | + | ret | |
| 824 | + | | |
| 825 | + | ; rest_chunks — D chunks of silence, timed to roughly match a note chunk so rests | |
| 826 | + | ; sit in the rhythm. | |
| 827 | + | rest_chunks: | |
| 828 | + | .rc_loop: | |
| 829 | + | ld b, 24 | |
| 830 | + | .rc_inner: | |
| 831 | + | ld e, 75 | |
| 832 | + | .rc_wait: | |
| 833 | + | dec e | |
| 834 | + | jr nz, .rc_wait | |
| 835 | + | djnz .rc_inner | |
| 836 | + | dec d | |
| 837 | + | jr nz, .rc_loop | |
| 807 | 838 | ret | |
| 839 | + | | |
| 840 | + | ; The theme — a short, solemn phrase in D minor. Pitch values are beep delay | |
| 841 | + | ; constants (larger = lower); durations are chunk counts. One voice, no harmony: | |
| 842 | + | ; the melody carries the whole mood by itself. | |
| 843 | + | theme: | |
| 844 | + | defb 75, 8 ; D5 | |
| 845 | + | defb 63, 8 ; F5 | |
| 846 | + | defb 50, 8 ; A5 | |
| 847 | + | defb 50, 12 ; A5 (held) | |
| 848 | + | defb 56, 8 ; G5 | |
| 849 | + | defb 63, 8 ; F5 | |
| 850 | + | defb 66, 8 ; E5 | |
| 851 | + | defb 75, 16 ; D5 (resolve) | |
| 852 | + | defb 0, 6 ; breath | |
| 853 | + | defb 56, 8 ; G5 | |
| 854 | + | defb 63, 8 ; F5 | |
| 855 | + | defb 50, 8 ; A5 | |
| 856 | + | defb 75, 16 ; D5 (home) | |
| 857 | + | defb $FF ; end | |
| 808 | 858 | | |
| 809 | 859 | gold_tile: | |
| 810 | 860 | defb %00000000 | |
| ... | |||
| 932 | 982 | ld b, 16 | |
| 933 | 983 | ld c, 6 | |
| 934 | 984 | call print_string | |
| 935 | - | .tt_wait: | |
| 985 | + | .tt_tune: | |
| 986 | + | ld hl, theme | |
| 987 | + | .tt_note: | |
| 936 | 988 | ld bc, KEYS_SPACE | |
| 937 | 989 | in a, (c) | |
| 938 | 990 | bit 0, a | |
| 939 | - | jr nz, .tt_wait | |
| 940 | - | .tt_rel: | |
| 941 | - | ld bc, KEYS_SPACE | |
| 991 | + | jr z, .tt_pressed ; SPACE down -> leave | |
| 992 | + | ld a, (hl) | |
| 993 | + | inc hl | |
| 994 | + | cp $FF | |
| 995 | + | jr z, .tt_tune ; end of tune -> loop it | |
| 996 | + | ld c, a | |
| 997 | + | ld a, (hl) | |
| 998 | + | inc hl | |
| 999 | + | ld d, a | |
| 1000 | + | ld a, c | |
| 1001 | + | or a | |
| 1002 | + | jr z, .tt_rest | |
| 1003 | + | push hl | |
| 1004 | + | call play_note | |
| 1005 | + | pop hl | |
| 1006 | + | jr .tt_note | |
| 1007 | + | .tt_rest: | |
| 1008 | + | push hl | |
| 1009 | + | call rest_chunks | |
| 1010 | + | pop hl | |
| 1011 | + | jr .tt_note | |
| 1012 | + | .tt_pressed: | |
| 1013 | + | ld bc, KEYS_SPACE ; debounce: wait for release | |
| 942 | 1014 | in a, (c) | |
| 943 | 1015 | bit 0, a | |
| 944 | - | jr z, .tt_rel | |
| 1016 | + | jr z, .tt_pressed | |
| 945 | 1017 | ret | |
| 946 | 1018 | | |
| 947 | 1019 | ; show_win — the keep is cleared. Black screen, the words, the flourish, then |
The complete program
; Shadowkeep — Unit 18: A Theme in One Voice
; Cumulative build; every step runs on its own. Narrative: the unit page.
; step-01 gives the title a voice — a solemn D-minor phrase, looping as it waits.
org 32768
WALL_ATTR equ %01001000
FLOOR_ATTR equ %00001000
MARK_ATTR equ %00001111
TORCH_ATTR equ %01001110 ; BRIGHT, blue paper, yellow ink — a lit sconce
STATUE_ATTR equ %01001111 ; BRIGHT white on blue — pale stone (solid)
BANNER_ATTR equ %01001011 ; BRIGHT magenta on blue — a hanging (solid)
RUBBLE_ATTR equ %00001000 ; dim, like floor — walkable broken stone
MAX_SHADE equ 4
MAX_TORCHES equ 4
THIEF equ %01001010
GOLD_ATTR equ %00000110 ; yellow ink, no BRIGHT -> walkable gold
TOTAL_GOLD equ 6
WARDEN equ %01000101 ; BRIGHT cyan on black — the sentinel
WARDEN_COL0 equ 26 ; the Hall's gold column
WARDEN_ROW0 equ 11
WARDEN_SPEED equ 10 ; frames between patrol steps
WARDEN_GATHER equ 50 ; a beat before it begins to move
AXIS_HORIZ equ 0 ; the Warden varies its column (walks a row)
AXIS_VERT equ 1 ; the Warden varies its row (walks a column)
WALL_BIT equ 6
START_COL equ 15
START_ROW equ 11
NO_EXIT equ $FF
KEYS_OP equ $DFFE
KEYS_Q equ $FBFE
KEYS_A equ $FDFE
KEYS_SPACE equ $7FFE
start:
ld a, 0
out ($FE), a
im 1
; --- TITLE -> PLAY -> WIN -> TITLE ------------------------------------------
main_title:
call show_title ; returns (interrupts off) when SPACE pressed
call new_game ; reset the keep, place the gold, draw
ei
.game_loop:
halt
ld a, (won)
or a
jr nz, .won
call player_step
call warden_step ; every room has its Warden now
ld a, (caught)
or a
jr nz, .lost
call mark_step
jr .game_loop
.lost:
call show_lose ; "THE KEEP SLEEPS", the sting, wait for SPACE
jr main_title
.won:
call show_win ; "THE KEEP STANDS", flourish, wait for SPACE
jr main_title ; round again
; new_game — copy the room templates back into working state (so collected gold
; returns), reset the thief, the gold counter and the win flag, draw the keep.
new_game:
ld hl, room0_template
ld de, room0_state
ld bc, 768
ldir
ld hl, room1_template
ld de, room1_state
ld bc, 768
ldir
ld hl, room2_template
ld de, room2_state
ld bc, 768
ldir
xor a
ld (current_room), a
ld (won), a
ld (caught), a
ld a, TOTAL_GOLD
ld (gold_remaining), a
ld a, START_COL
ld (thief_col), a
ld a, START_ROW
ld (thief_row), a
call draw_room
call save_under
call draw_thief
call warden_enter ; this room's Warden, from the table
call save_warden
call draw_warden
ret
mark_step:
ld bc, KEYS_SPACE
in a, (c)
bit 0, a
ret nz
call cell_state_addr
ld (hl), '+'
ld hl, mark_tile
ld de, under_thief
ld bc, 8
ldir
ld a, MARK_ATTR
ld (under_thief + 8), a
ret
cell_state_addr:
call room_entry_addr
ld a, (hl)
inc hl
ld h, (hl)
ld l, a
push hl
ld a, (thief_row)
ld l, a
ld h, 0
add hl, hl
add hl, hl
add hl, hl
add hl, hl
add hl, hl
ld a, (thief_col)
ld e, a
ld d, 0
add hl, de
pop de
add hl, de
ret
room_entry_addr:
ld a, (current_room)
ld l, a
ld h, 0
ld d, h
ld e, l
add hl, hl
add hl, de
add hl, hl
ld de, rooms
add hl, de
ret
; ----------------------------------------------------------------------------
; find_torch — scan the current room's map for 'T', remember where it is (or
; NO_TORCH if the room is unlit).
; ----------------------------------------------------------------------------
; find_torches — collect every 'T' in the current room (up to MAX_TORCHES) into
; torch_list as (col, row) pairs; torch_count says how many.
find_torches:
xor a
ld (torch_count), a
call room_entry_addr
ld a, (hl)
inc hl
ld h, (hl)
ld l, a
ld b, 0
.fr_row:
ld c, 0
.fr_col:
ld a, (hl)
cp 'T'
jr nz, .fr_skip
ld a, (torch_count)
cp MAX_TORCHES
jr nc, .fr_skip
push hl
add a, a ; count * 2
ld e, a
ld d, 0
ld hl, torch_list
add hl, de
ld (hl), c ; column
inc hl
ld (hl), b ; row
pop hl
ld a, (torch_count)
inc a
ld (torch_count), a
.fr_skip:
inc hl
inc c
ld a, c
cp 32
jr nz, .fr_col
inc b
ld a, b
cp 24
jr nz, .fr_row
ret
; ----------------------------------------------------------------------------
; shade_for_cell — row in B, column in C. Returns a shade 0..4 in A: the
; Chebyshev distance to the torch, halved and clamped. Near the flame = 0
; (lightest); far away = 4 (darkest). No torch = darkest everywhere.
; ----------------------------------------------------------------------------
shade_for_cell:
push bc
ld a, b
ld (cell_row), a
ld a, c
ld (cell_col), a
ld a, (torch_count)
or a
jr z, .sf_dark
ld a, 255
ld (min_dist), a
ld hl, torch_list
ld a, (torch_count)
ld b, a ; loop count
.sf_loop:
ld a, (cell_col)
sub (hl) ; - torch col
jr nc, .sf_dc
neg
.sf_dc:
ld d, a ; |dc|
inc hl ; -> torch row
ld a, (cell_row)
sub (hl)
jr nc, .sf_dr
neg
.sf_dr:
inc hl ; -> next torch pair
cp d ; A = |dr|; take the larger
jr nc, .sf_mx
ld a, d
.sf_mx:
ld e, a ; this torch's distance
ld a, (min_dist)
cp e
jr c, .sf_keep ; min already smaller
ld a, e
ld (min_dist), a
.sf_keep:
djnz .sf_loop
ld a, (current_room)
ld c, a
ld b, 0
ld hl, room_falloff
add hl, bc
ld b, (hl)
ld a, (min_dist)
inc b
.sf_shift:
dec b
jr z, .sf_clamp
srl a
jr .sf_shift
.sf_clamp:
cp MAX_SHADE + 1
jr c, .sf_done
ld a, MAX_SHADE
.sf_done:
pop bc
ret
.sf_dark:
ld a, MAX_SHADE
pop bc
ret
draw_room:
call find_torches
call room_entry_addr
ld a, (hl)
inc hl
ld h, (hl)
ld l, a
ld (map_ptr), hl
ld b, 0
.room_row:
ld c, 0
.room_col:
ld hl, (map_ptr)
ld a, (hl)
cp '.'
jr nz, .not_floor
call shade_for_cell
add a, a
ld e, a
ld d, 0
ld hl, shade_tiles
add hl, de
ld e, (hl)
inc hl
ld d, (hl)
ld (tile_ptr), de
ld a, FLOOR_ATTR
ld (tile_attr), a
call draw_tile
jr .cell_done
.not_floor:
call lookup_tile
call draw_tile
.cell_done:
ld hl, (map_ptr)
inc hl
ld (map_ptr), hl
inc c
ld a, c
cp 32
jr nz, .room_col
inc b
ld a, b
cp 24
jr nz, .room_row
ret
lookup_tile:
ld hl, palette
.scan:
cp (hl)
jr z, .found
inc hl
inc hl
inc hl
inc hl
jr .scan
.found:
inc hl
ld e, (hl)
inc hl
ld d, (hl)
ld (tile_ptr), de
inc hl
ld a, (hl)
ld (tile_attr), a
ret
draw_tile:
push bc
call attr_addr_cr
ld a, (tile_attr)
ld (hl), a
call scr_addr_cr
ld de, (tile_ptr)
ld b, 8
.tile_row:
ld a, (de)
ld (hl), a
inc de
inc h
djnz .tile_row
pop bc
ret
player_step:
ld a, (thief_col)
ld (tcol), a
ld a, (thief_row)
ld (trow), a
ld bc, KEYS_OP
in a, (c)
bit 1, a
jr z, .left
bit 0, a
jr z, .right
ld bc, KEYS_Q
in a, (c)
bit 0, a
jr z, .up
ld bc, KEYS_A
in a, (c)
bit 0, a
jr z, .down
ret
.left:
ld hl, tcol
dec (hl)
jr .move
.right:
ld hl, tcol
inc (hl)
jr .move
.up:
ld hl, trow
dec (hl)
jr .move
.down:
ld hl, trow
inc (hl)
.move:
ld a, (trow)
ld b, a
ld a, (tcol)
ld c, a
call wall_at
ret nz
call restore_under
ld a, (tcol)
ld (thief_col), a
ld a, (trow)
ld (thief_row), a
call collect_gold ; the new cell might be gold — lift it first
call save_under
call draw_thief
call sfx_step
call check_exit
ret
wall_at:
call attr_addr_cr
bit WALL_BIT, (hl)
ret
check_exit:
ld a, (thief_col)
or a
jr z, .west
cp 31
jr z, .east
ld a, (thief_row)
or a
jr z, .north
cp 23
jr z, .south
ret
.east:
call room_entry_addr
ld de, 4
add hl, de
ld a, (hl)
cp NO_EXIT
ret z
ld (current_room), a
ld a, 1
ld (thief_col), a
jr .enter
.west:
call room_entry_addr
ld de, 5
add hl, de
ld a, (hl)
cp NO_EXIT
ret z
ld (current_room), a
ld a, 30
ld (thief_col), a
jr .enter
.north:
call room_entry_addr
inc hl
inc hl
ld a, (hl)
cp NO_EXIT
ret z
ld (current_room), a
ld a, 22
ld (thief_row), a
jr .enter
.south:
call room_entry_addr
inc hl
inc hl
inc hl
ld a, (hl)
cp NO_EXIT
ret z
ld (current_room), a
ld a, 1
ld (thief_row), a
.enter:
call sfx_door
call draw_room
call save_under
call draw_thief
call warden_enter ; this room's Warden, clear of the entry cell
call save_warden
call draw_warden
ret
pos_bc:
ld a, (thief_row)
ld b, a
ld a, (thief_col)
ld c, a
ret
save_under:
call pos_bc
call scr_addr_cr
ld de, under_thief
ld b, 8
.save_row:
ld a, (hl)
ld (de), a
inc de
inc h
djnz .save_row
call pos_bc
call attr_addr_cr
ld a, (hl)
ld (under_thief + 8), a
ret
restore_under:
call pos_bc
call scr_addr_cr
ld de, under_thief
ld b, 8
.restore_row:
ld a, (de)
ld (hl), a
inc de
inc h
djnz .restore_row
call pos_bc
call attr_addr_cr
ld a, (under_thief + 8)
ld (hl), a
ret
draw_thief:
call pos_bc
call attr_addr_cr
ld (hl), THIEF
call pos_bc
call scr_addr_cr
ld de, thief
ld b, 8
.thief_row:
ld a, (de)
ld (hl), a
inc de
inc h
djnz .thief_row
ret
; ----------------------------------------------------------------------------
; The Warden — something shares the keep. A second mover, drawn exactly like the
; thief: a private under-buffer and its own save / draw, a spectral hooded
; sentinel. First we simply give it a body (it neither moves nor harms yet).
; ----------------------------------------------------------------------------
wpos_bc:
ld a, (warden_row)
ld b, a
ld a, (warden_col)
ld c, a
ret
save_warden:
call wpos_bc
call scr_addr_cr
ld de, under_warden
ld b, 8
.svw_row:
ld a, (hl)
ld (de), a
inc de
inc h
djnz .svw_row
call wpos_bc
call attr_addr_cr
ld a, (hl)
ld (under_warden + 8), a
ret
draw_warden:
call wpos_bc
call attr_addr_cr
ld (hl), WARDEN
call wpos_bc
call scr_addr_cr
ld de, warden_glyph
ld b, 8
.drw_row:
ld a, (de)
ld (hl), a
inc de
inc h
djnz .drw_row
ret
; A spectral hooded sentinel: a cowl with dark eye-slits over a robe that frays
; at the hem. Cold, faceless, unmistakably a figure.
warden_glyph:
defb %00111100
defb %01111110
defb %01100110
defb %01111110
defb %00111100
defb %01111110
defb %01111110
defb %01011010
restore_warden:
call wpos_bc
call scr_addr_cr
ld de, under_warden
ld b, 8
.rsw_row:
ld a, (de)
ld (hl), a
inc de
inc h
djnz .rsw_row
call wpos_bc
call attr_addr_cr
ld a, (under_warden + 8)
ld (hl), a
ret
; warden_step — the patrol. Walks its column one cell every WARDEN_SPEED frames,
; after a WARDEN_GATHER beat, reversing at walls. Deterministic: a route you learn
; and time. It reads the thief's cell as a wall (his attribute has WALL_BIT set),
; so it turns aside at him for now — the catch is Unit 11.
warden_step:
ld a, (warden_timer)
dec a
ld (warden_timer), a
ret nz
ld a, WARDEN_SPEED
ld (warden_timer), a
; propose the next cell along the patrol axis, in the current dir
ld a, (warden_axis)
or a
jr nz, .ws_vert
.ws_horiz:
ld a, (warden_row)
ld b, a ; B = row (fixed)
ld a, (warden_dir)
ld hl, warden_col
add a, (hl)
ld c, a ; C = next col
jr .ws_have
.ws_vert:
ld a, (warden_col)
ld c, a ; C = col (fixed)
ld a, (warden_dir)
ld hl, warden_row
add a, (hl)
ld b, a ; B = next row
.ws_have:
ld a, b ; the thief there? caught — check BEFORE
ld hl, thief_row ; wall_at, because his own cell reads as wall
cp (hl)
jr nz, .ws_wall
ld a, c
ld hl, thief_col
cp (hl)
jr nz, .ws_wall
ld a, 1
ld (caught), a
ret
.ws_wall:
push bc
call wall_at
pop bc
jr z, .ws_commit ; floor ahead — step onto it
ld a, (warden_dir) ; wall ahead — reverse, wait a beat
neg
ld (warden_dir), a
ret
.ws_commit:
push bc ; keep the proposed (row B, col C)
call restore_warden
pop bc
ld a, c
ld (warden_col), a
ld a, b
ld (warden_row), a
call save_warden ; photograph the new cell's ground
call draw_warden
ret
; ----------------------------------------------------------------------------
; warden_enter — instantiate the current room's Warden from warden_table: place
; it at the route-start (chosen clear of the entry cell), set its axis, and start
; its gather. Called on new_game and on every room change. A second mover is a
; table entry — like the torches and the gold.
; ----------------------------------------------------------------------------
warden_enter:
ld a, (current_room)
add a, a
add a, a ; * 4 bytes per table row
ld e, a
ld d, 0
ld hl, warden_table
add hl, de
ld a, (hl)
ld (warden_col), a
inc hl
ld a, (hl)
ld (warden_row), a
inc hl
ld a, (hl)
ld (warden_dir), a
inc hl
ld a, (hl)
ld (warden_axis), a
ld a, WARDEN_GATHER
ld (warden_timer), a
ret
; warden_table — one row per room: start col, start row, dir (+1/-1), axis.
; Each route crosses that room's gold and starts clear of the entry cell.
warden_table:
defb WARDEN_COL0, WARDEN_ROW0, -1, AXIS_VERT ; Hall — the gold's column
defb 24, 15, -1, AXIS_VERT ; Gallery — column 24, lower chamber
defb 15, 20, -1, AXIS_HORIZ ; Vault — row 20, between the coins
; ----------------------------------------------------------------------------
; The gold — the keep's goal. Step onto a coin and it lifts: the map cell turns
; to floor (gone for good), the cell repaints as plain floor (no lighting yet),
; a chime sounds, and the counter ticks down.
; ----------------------------------------------------------------------------
collect_gold:
call cell_state_addr ; HL -> map cell at the thief's position
ld a, (hl)
cp 'G'
ret nz
ld (hl), '.' ; the gold is taken — floor from now on
call pos_bc ; B = row, C = col
call draw_floor_cell ; repaint the cell as plain floor
call sfx_pickup
ld hl, gold_remaining
dec (hl)
ld a, (hl)
or a
call z, win ; the last coin — the keep stands
ret
; draw_floor_cell — paint the floor tile at (row B, col C). Lighting (Unit 13)
; will replace this with a shade chosen by distance from the nearest torch.
draw_floor_cell:
call shade_for_cell
add a, a
ld e, a
ld d, 0
ld hl, shade_tiles
add hl, de
ld e, (hl)
inc hl
ld d, (hl)
ld (tile_ptr), de
ld a, FLOOR_ATTR
ld (tile_attr), a
call draw_tile
ret
; ----------------------------------------------------------------------------
; beep — the one tone primitive (the tiny game's blip, reused). B = cycles,
; C = the delay between speaker toggles (the pitch; larger C = lower).
; ----------------------------------------------------------------------------
beep:
.bp_cycle:
ld a, %00010000
out ($FE), a
ld e, c
.bp_hi:
dec e
jr nz, .bp_hi
xor a
out ($FE), a
ld e, c
.bp_lo:
dec e
jr nz, .bp_lo
djnz .bp_cycle
ret
; sfx_pickup — a bright two-blip chime: the sound of gold.
sfx_pickup:
ld b, 8
ld c, 20
call beep
ld b, 8
ld c, 14
call beep
ret
; sfx_step — a footfall: short and low, gone almost before you notice it. Played
; under every successful move.
sfx_step:
ld b, 5
ld c, 90
call beep
ret
; sfx_door — a creak: a tone that falls in pitch as it plays, so the note groans
; downward — a heavy door swinging on its hinges.
sfx_door:
ld c, 36 ; start higher
.sd_sweep:
ld b, 3
push bc
call beep
pop bc
inc c ; lower the pitch a little
inc c
ld a, c
cp 130 ; until it has groaned down low
jr c, .sd_sweep
ret
; ----------------------------------------------------------------------------
; The music player — a note-table interpreter for the title theme.
; play_note — C = pitch (beep delay), D = duration in chunks. A note is the beep
; primitive run for D fixed-size chunks, so a note can be long though one beep's
; cycle count is a single byte.
; ----------------------------------------------------------------------------
play_note:
.pn_loop:
ld b, 24 ; one chunk = 24 square-wave cycles
push de
call beep ; B cycles at pitch C
pop de
dec d
jr nz, .pn_loop
ret
; rest_chunks — D chunks of silence, timed to roughly match a note chunk so rests
; sit in the rhythm.
rest_chunks:
.rc_loop:
ld b, 24
.rc_inner:
ld e, 75
.rc_wait:
dec e
jr nz, .rc_wait
djnz .rc_inner
dec d
jr nz, .rc_loop
ret
; The theme — a short, solemn phrase in D minor. Pitch values are beep delay
; constants (larger = lower); durations are chunk counts. One voice, no harmony:
; the melody carries the whole mood by itself.
theme:
defb 75, 8 ; D5
defb 63, 8 ; F5
defb 50, 8 ; A5
defb 50, 12 ; A5 (held)
defb 56, 8 ; G5
defb 63, 8 ; F5
defb 66, 8 ; E5
defb 75, 16 ; D5 (resolve)
defb 0, 6 ; breath
defb 56, 8 ; G5
defb 63, 8 ; F5
defb 50, 8 ; A5
defb 75, 16 ; D5 (home)
defb $FF ; end
gold_tile:
defb %00000000
defb %00111100
defb %01111110
defb %01111110
defb %01111110
defb %01111110
defb %00111100
defb %00000000
; One byte of mood per room: how slowly its light fades.
room_falloff:
defb 2 ; Hall — broad, soft pool
defb 1 ; Gallery — medium
defb 0 ; Vault — tight pool, deep dark
; The shade ramp: lightest (lit) to darkest (deep shadow), all blue/black dither.
shade_tiles:
defw shade0_tile
defw shade1_tile
defw shade2_tile
defw shade3_tile
defw shade4_tile
shade0_tile: ; lit — nearly all blue
defb %00000000
defb %00100010
defb %00000000
defb %00000000
defb %00000000
defb %10001000
defb %00000000
defb %00000000
shade1_tile:
defb %00100010
defb %00000000
defb %10001000
defb %00000000
defb %00100010
defb %00000000
defb %10001000
defb %00000000
shade2_tile: ; the half-and-half slate from Unit 2
defb %10101010
defb %01010101
defb %10101010
defb %01010101
defb %10101010
defb %01010101
defb %10101010
defb %01010101
shade3_tile:
defb %10101010
defb %11111111
defb %01010101
defb %11111111
defb %10101010
defb %11111111
defb %01010101
defb %11111111
shade4_tile: ; deep shadow — nearly all black
defb %11111111
defb %11101110
defb %11111111
defb %10111011
defb %11111111
defb %11101110
defb %11111111
defb %10111011
torch_tile: ; a flame in its sconce
defb %00010000
defb %00111000
defb %00111000
defb %01111100
defb %01111100
defb %01111100
defb %00111000
defb %00010000
statue_tile:
defb %00111100
defb %01111110
defb %00111100
defb %00011000
defb %00011000
defb %00111100
defb %01111110
defb %01111110
banner_tile:
defb %01111110
defb %01111110
defb %01011010
defb %01011010
defb %01111110
defb %01111110
defb %00111100
defb %00011000
rubble_tile:
defb %00000000
defb %01100000
defb %01100000
defb %00000110
defb %00000110
defb %00011000
defb %00011000
defb %00000000
; ----------------------------------------------------------------------------
; show_title — black screen, the keep's name and a prompt; wait for SPACE (and
; release). Silent for now — the composed theme arrives in Unit 18. Words use the
; ROM's own 8x8 font at $3D00.
; ----------------------------------------------------------------------------
show_title:
di
call clear_screen
ld hl, str_title
ld b, 8
ld c, 11
call print_string
ld hl, str_prompt
ld b, 16
ld c, 6
call print_string
.tt_tune:
ld hl, theme
.tt_note:
ld bc, KEYS_SPACE
in a, (c)
bit 0, a
jr z, .tt_pressed ; SPACE down -> leave
ld a, (hl)
inc hl
cp $FF
jr z, .tt_tune ; end of tune -> loop it
ld c, a
ld a, (hl)
inc hl
ld d, a
ld a, c
or a
jr z, .tt_rest
push hl
call play_note
pop hl
jr .tt_note
.tt_rest:
push hl
call rest_chunks
pop hl
jr .tt_note
.tt_pressed:
ld bc, KEYS_SPACE ; debounce: wait for release
in a, (c)
bit 0, a
jr z, .tt_pressed
ret
; show_win — the keep is cleared. Black screen, the words, the flourish, then
; wait for SPACE (and release) to return to the title.
show_win:
di
call clear_screen
ld hl, str_won
ld b, 9
ld c, 8
call print_string
ld hl, str_again
ld b, 15
ld c, 5
call print_string
call sfx_win
.sw_wait:
ld bc, KEYS_SPACE
in a, (c)
bit 0, a
jr nz, .sw_wait
.sw_rel:
ld bc, KEYS_SPACE
in a, (c)
bit 0, a
jr z, .sw_rel
ret
; win — the last coin is gone. Flourish, and raise the flag the loop watches.
win:
ld a, 1
ld (won), a
call sfx_win
ret
; sfx_win — an ascending flourish: a low note climbing in steps to a high one.
sfx_win:
ld c, 60
.swf_loop:
ld b, 12
push bc
call beep
pop bc
ld a, c
sub 8
ld c, a
cp 16
jr nc, .swf_loop
ret
; clear_screen — fill bitmap and attributes with zero: a black screen.
clear_screen:
ld hl, $4000
ld (hl), 0
ld de, $4001
ld bc, 6911
ldir
ret
; print_string — HL -> zero-terminated text, B = row, C = col.
print_string:
.ps_loop:
ld a, (hl)
or a
ret z
push hl
call print_char
pop hl
inc hl
inc c
jr .ps_loop
; print_char — A = character (32..127), B = row, C = col. Copies the ROM font
; glyph at $3D00 + (char-32)*8 to the screen, bright white.
print_char:
push bc
sub 32
ld l, a
ld h, 0
add hl, hl
add hl, hl
add hl, hl
ld de, $3D00
add hl, de
push hl
call scr_addr_cr
pop de
ld b, 8
.pc_row:
ld a, (de)
ld (hl), a
inc de
inc h
djnz .pc_row
pop bc
call attr_addr_cr
ld (hl), %01000111
ret
str_title:
defb "SHADOWKEEP", 0
str_prompt:
defb "PRESS SPACE TO ENTER", 0
str_won:
defb "THE KEEP STANDS", 0
str_again:
defb "PRESS SPACE TO RETURN", 0
; ----------------------------------------------------------------------------
; show_lose — the mirror of show_win. Black screen, the words, the freezing
; sting, then wait for SPACE (and release) to return to the title.
; ----------------------------------------------------------------------------
show_lose:
di
call clear_screen
ld hl, str_lost
ld b, 9
ld c, 8
call print_string
ld hl, str_again
ld b, 15
ld c, 5
call print_string
call sfx_caught
.slo_wait:
ld bc, KEYS_SPACE
in a, (c)
bit 0, a
jr nz, .slo_wait
.slo_rel:
ld bc, KEYS_SPACE
in a, (c)
bit 0, a
jr z, .slo_rel
ret
; sfx_caught — the plunge into stasis: a quick fall, then a deep, long toll as
; the stone closes over you. The opposite of the win flourish.
sfx_caught:
ld c, 16
.sca_fall:
ld b, 5
push bc
call beep
pop bc
ld a, c
add a, 7
ld c, a
cp 100
jr c, .sca_fall
ld b, 60
ld c, 130
call beep
ret
str_lost:
defb "THE KEEP SLEEPS", 0
scr_addr_cr:
ld a, b
and %00011000
or %01000000
ld h, a
ld a, b
and %00000111
rrca
rrca
rrca
or c
ld l, a
ret
attr_addr_cr:
ld a, b
ld l, a
ld h, 0
add hl, hl
add hl, hl
add hl, hl
add hl, hl
add hl, hl
ld de, $5800
add hl, de
ld a, c
ld e, a
ld d, 0
add hl, de
ret
palette:
defb '.'
defw floor_tile
defb FLOOR_ATTR
defb '#'
defw wall_tile
defb WALL_ATTR
defb '+'
defw mark_tile
defb MARK_ATTR
defb 'G'
defw gold_tile
defb GOLD_ATTR
defb 'T'
defw torch_tile
defb TORCH_ATTR
defb 'S'
defw statue_tile
defb STATUE_ATTR
defb 'B'
defw banner_tile
defb BANNER_ATTR
defb 'o'
defw rubble_tile
defb RUBBLE_ATTR
; ----------------------------------------------------------------------------
; The keep: three rooms. Hall -east-> Gallery -north-> Vault, and back.
; entry: map ptr, North, South, East, West
; ----------------------------------------------------------------------------
rooms:
defw room0_state
defb NO_EXIT, NO_EXIT, 1, NO_EXIT ; Hall: east -> Gallery
defw room1_state
defb 2, NO_EXIT, NO_EXIT, 0 ; Gallery: north -> Vault, west -> Hall
defw room2_state
defb NO_EXIT, 1, NO_EXIT, NO_EXIT ; Vault: south -> Gallery
; The Great Hall — four pillars, east door at row 11.
room0_template:
defb "###############T################"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "B..............S...............B"
defb "#.............ooo.........G....#"
defb "#..............................#"
defb "T........##..........##........T"
defb "#........##..........##........#"
defb "#..............................#"
defb "#..............................."
defb "#..............................#"
defb "#..............................#"
defb "#........##..........##........#"
defb "#........##..........##........#"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "#.........................G....#"
defb "#..............................#"
defb "#..............................#"
defb "################################"
; The Gallery — a dividing wall with one gap (column 15). West door (row 11)
; back to the Hall; north door (column 15) up to the Vault.
room1_template:
defb "###############.################"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "#..............................T"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "###############.################"
defb "#..............................#"
defb "#..............................#"
defb "........................G......#"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "B..............................#"
defb "#..............................#"
defb "#..............................#"
defb "#........................ooo...#"
defb "#..............................#"
defb "#.......................G......#"
defb "#..............................#"
defb "#..............................#"
defb "###############T################"
; The Vault — a great altar of stone in the middle, south door (column 15)
; down to the Gallery.
room2_template:
defb "################################"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "#.............#T##.............#"
defb "#.............####.............#"
defb "#.............####.............#"
defb "#.............####.............#"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "#.........G.........G..........#"
defb "#..............................#"
defb "#..............................#"
defb "###############.################"
floor_tile:
defb %10101010
defb %01010101
defb %10101010
defb %01010101
defb %10101010
defb %01010101
defb %10101010
defb %01010101
wall_tile:
defb %00010001
defb %00000000
defb %01000100
defb %00000000
defb %00010001
defb %00000000
defb %01000100
defb %00000000
mark_tile:
defb %00000000
defb %00011000
defb %00011000
defb %01111110
defb %01111110
defb %00011000
defb %00011000
defb %00000000
thief:
defb %00011000
defb %00111100
defb %01111110
defb %01111110
defb %01111110
defb %01111110
defb %00111100
defb %00100100
current_room:
defb 0
thief_col:
defb START_COL
thief_row:
defb START_ROW
tcol:
defb 0
trow:
defb 0
map_ptr:
defw 0
tile_ptr:
defw 0
tile_attr:
defb 0
under_thief:
defb 0, 0, 0, 0, 0, 0, 0, 0, 0
gold_remaining:
defb TOTAL_GOLD
won:
defb 0
under_warden:
defb 0, 0, 0, 0, 0, 0, 0, 0, 0
warden_col:
defb WARDEN_COL0
warden_row:
defb WARDEN_ROW0
warden_dir:
defb -1
warden_axis:
defb AXIS_VERT
warden_timer:
defb WARDEN_GATHER
caught:
defb 0
torch_count:
defb 0
cell_row:
defb 0
cell_col:
defb 0
min_dist:
defb 0
torch_list:
defs MAX_TORCHES * 2
room0_state:
defs 768
room1_state:
defs 768
room2_state:
defs 768
end start
The theme, looping under the title — one voice, rising through the D-minor triad to a held note, then stepping home, then round again:
Press SPACE and the game begins as before — explore, collect, hold back the dark, win or sleep. The keep now has a voice that’s its own, not a generic blip.
A note on interrupts. We
di(disable interrupts) for the title’s music and onlyim 1/eiafterwards, for the game loop. The 50 Hz interrupt would otherwise tick across every note and roughen the tune. Music wants the CPU’s full attention; the game loop wants the interrupt back forhalt. Each gets what it needs.
Try this: change the key
Shift every pitch value up or down by the same proportion and the whole theme transposes — higher and brighter, or lower and grimmer. The shape (the intervals between notes) is the melody; the absolute pitches are just where you pin it. Try it lower for a darker keep.
Try this: a longer phrase
The theme is a dozen notes. Extend it — a second phrase that answers the first, a turn that climbs before it resolves. Watch that it still loops cleanly: the last note should lead back to the first without a jolt. Writing a loop that doesn’t announce its seam is a craft of its own.
Try this: a darker resolve
The theme ends home on D — safe, resolved. Try ending it on a note not home — the F or the A — so it hangs, unresolved, uneasy. A theme that never settles is a keep that never lets you relax. The last note is the feeling you leave the player holding.
When it’s wrong, see why
- The tune plays once and stops. The loop isn’t returning to the theme’s start on
$FF— it should reset to the top, not fall through. - SPACE is ignored during the music. The keyboard check isn’t between notes — it must run each time round the note loop, not only before or after the whole tune.
- The notes run together into a smear. No gap between them, or the interrupt is still firing. Add a short rest between notes, and
difor the music. - A rest plays as a note. Pitch
0must be treated as silence (a rest), not fed tobeepas a pitch. - The tune is lumpy and uneven. Durations aren’t matched to the feel — a chunk count is rhythm, so uneven counts read as uneven timing. Tune them by ear.
Before and after
You started with a keep that opened in silence and finished with one that announces itself — a short D-minor phrase looping under the title, one voice carrying the whole mood, and breaking off the instant you press to play. The tool was the beeper you already click footsteps with; the new work was a note player that stacks chunks into notes and a wait-loop that doubles as the tune, checking your keypress between every note. Music on one bit is all composition and discipline — no harmony to hide behind, no press allowed to fall through the cracks. The keep has a voice now, and it’s unmistakably its own.
What you’ve learnt
- A note is a stack of beeps. One
beepis too short to hold; count chunks of it, and the count is your rhythm. - Monophonic means the melody carries everything. One voice, no harmony — mood, rhythm and identity all ride a single line.
- The wait-loop is the player. Interleave the tune with the keypress check so the theme loops and the press is never swallowed — the discipline a title tune owes the player.
- Music wants the CPU; the loop wants the interrupt.
difor the tune,eifor the game — each gets the machine on its own terms.
What’s next
The keep plays, sounds, lights, and sings — everything is here but the seal on it. In Unit 19, “Stand or Sleep,” we crown the title with a hand-pixelled band of stone and prove the whole thing the way the course demands: a run to each ending, THE KEEP STANDS and THE KEEP SLEEPS, both reachable and both real. It’s the unit where “a complete, finishable game” becomes true out loud — losable and winnable, and finished.