A score table needs a clear answer for ties, a full table and the player who just misses the cut.
Use it in a project
Maintain up to four descending unsigned byte scores with associated byte tags. Insert after existing equal scores. Return RANK 0–3 and INSERTED=1 when retained; otherwise RANK=255. COUNT>4 is invalid. Entries beyond COUNT are unused; the existing prefix must be sorted.
Include component.inc once (MOS callers include the shared 6502 implementation through it). Reserve the public fields in this exact order: RANK, INSERTED, VALID, SCORE, TAG, COUNT, S0, S1, S2, S3, I0, I1, I2, I3. They occupy 14 contiguous bytes. Also reserve the private workspace: T0, T1, T2, T3, EXPR_SAVE (5 bytes). Array names in the explanation refer to the numbered consecutive bindings, such as C0, C1 and so on.
Call high_score_insertion_init once at the intended reset boundary. It clears inputs as well as outputs and workspace. Set your starting state and configuration afterwards, then call high_score_insertion_step whenever the described event occurs. The helper reads no device, waits for no frame and installs no interrupt handler.
| Ownership | Fields |
|---|---|
| Retain between calls | COUNT, S0..S3 and I0..I3 |
| Supply before service | SCORE and TAG |
| Read after service | RANK, INSERTED and VALID |
Find the first strictly smaller score, then move the tail backwards so no source entry is overwritten before it has been copied.
Reusable initialisation and service
; SPDX-License-Identifier: MIT
; Insert into a High-score Table. See README.md for the byte interface and ownership.
; init clears the public fields and private workspace; set inputs afterwards.
high_score_insertion_init:
lda #0
sta RANK
sta INSERTED
sta VALID
sta SCORE
sta TAG
sta COUNT
sta S0
sta S1
sta S2
sta S3
sta I0
sta I1
sta I2
sta I3
sta T0
sta T1
sta T2
sta T3
sta EXPR_SAVE
rts
high_score_insertion_step:
; RANK = 255
lda #255
sta RANK
; INSERTED = 0
lda #0
sta INSERTED
; VALID = 0
lda #0
sta VALID
; if COUNT > 4:
lda COUNT
cmp #4
beq high_score_insertion_L5
bcs high_score_insertion_L4
high_score_insertion_L5:
jmp high_score_insertion_L2
high_score_insertion_L4:
jmp high_score_insertion_L1
high_score_insertion_L1:
; return
rts
jmp high_score_insertion_L3
high_score_insertion_L2:
high_score_insertion_L3:
; VALID = 1
lda #1
sta VALID
; T0 = 0
lda #0
sta T0
; while T0 < COUNT:
high_score_insertion_L6:
lda T0
cmp COUNT
bcc high_score_insertion_L9
high_score_insertion_L10:
jmp high_score_insertion_L8
high_score_insertion_L9:
jmp high_score_insertion_L7
high_score_insertion_L7:
; T1 = S[T0]
ldx T0
lda S0,x
sta T1
; if SCORE > T1:
lda SCORE
cmp T1
beq high_score_insertion_L15
bcs high_score_insertion_L14
high_score_insertion_L15:
jmp high_score_insertion_L12
high_score_insertion_L14:
jmp high_score_insertion_L11
high_score_insertion_L11:
; break
jmp high_score_insertion_L8
jmp high_score_insertion_L13
high_score_insertion_L12:
high_score_insertion_L13:
; T0 = T0 + 1
lda T0
clc
adc #1
sta T0
jmp high_score_insertion_L6
high_score_insertion_L8:
; if T0 >= 4:
lda T0
cmp #4
bcs high_score_insertion_L19
high_score_insertion_L20:
jmp high_score_insertion_L17
high_score_insertion_L19:
jmp high_score_insertion_L16
high_score_insertion_L16:
; return
rts
jmp high_score_insertion_L18
high_score_insertion_L17:
high_score_insertion_L18:
; RANK = T0
lda T0
sta RANK
; if COUNT < 4:
lda COUNT
cmp #4
bcc high_score_insertion_L24
high_score_insertion_L25:
jmp high_score_insertion_L22
high_score_insertion_L24:
jmp high_score_insertion_L21
high_score_insertion_L21:
; COUNT = COUNT + 1
lda COUNT
clc
adc #1
sta COUNT
jmp high_score_insertion_L23
high_score_insertion_L22:
high_score_insertion_L23:
; T1 = COUNT - 1
lda COUNT
sec
sbc #1
sta T1
; while T1 > T0:
high_score_insertion_L26:
lda T1
cmp T0
beq high_score_insertion_L30
bcs high_score_insertion_L29
high_score_insertion_L30:
jmp high_score_insertion_L28
high_score_insertion_L29:
jmp high_score_insertion_L27
high_score_insertion_L27:
; T2 = T1 - 1
lda T1
sec
sbc #1
sta T2
; T3 = S[T2]
ldx T2
lda S0,x
sta T3
; S[T1] = T3
lda T3
sta EXPR_SAVE
ldx T1
lda EXPR_SAVE
sta S0,x
; T3 = I[T2]
ldx T2
lda I0,x
sta T3
; I[T1] = T3
lda T3
sta EXPR_SAVE
ldx T1
lda EXPR_SAVE
sta I0,x
; T1 = T1 - 1
lda T1
sec
sbc #1
sta T1
jmp high_score_insertion_L26
high_score_insertion_L28:
; S[T0] = SCORE
lda SCORE
sta EXPR_SAVE
ldx T0
lda EXPR_SAVE
sta S0,x
; I[T0] = TAG
lda TAG
sta EXPR_SAVE
ldx T0
lda EXPR_SAVE
sta I0,x
; INSERTED = 1
lda #1
sta INSERTED
rts
component_end:Machine contract
A/X/status may change; Y is preserved. The 2A03 has no decimal arithmetic mode. A direct JSR needs two return-address stack bytes. The helper makes no nested calls and adds no other stack use. Its named scratch is private workspace, not a pointer, a ROM variable or shared zero-page space that the game may borrow concurrently. The samples use fixed symbol bindings. Scope or rename every label and binding, including the component_end measurement marker, and allocate a separate block for each independent instance. Different helpers can also use common field names, so combining them needs separate namespaces or explicitly renamed bindings. Give each block one mutation owner.
The NROM caller owns PPU setup and background display, with NMI and DMC disabled. Table and packet sizes are bounded to fit the cartridge caller and internal RAM; the helper owns no PPU registers.
Adapt the caller
demo.asm supplies the bindings and include order. exercise.inc first runs table cases, then a separate client retaining state between calls. A game can call the public step entry directly and remove the diagnostic packet and display. Do not copy the diagnostic’s hardware takeover into an existing game loop.
Build with make ASM198X=/path/to/asm198x. The Makefile produces normal, custom, deliberately wrong and repaired programs. Tools must already be installed; the sample downloads nothing.
Bindings and include order
.segment "HEADER"
.byte "NES",$1a,2,1,0,0,0,0,0,0,0,0,0,0
RANK=$80
INSERTED=$81
VALID=$82
SCORE=$83
TAG=$84
COUNT=$85
S0=$86
S1=$87
S2=$88
S3=$89
I0=$8a
I1=$8b
I2=$8c
I3=$8d
T0=$8e
T1=$8f
T2=$90
T3=$91
EXPR_SAVE=$92
STATE=$80
input_ptr=$70
cases_left=$72
ptr=$74
saved_y=$76
OUTPUT=$0200
preview=OUTPUT+1400
ready=OUTPUT+1408
CUSTOM=0
BROKEN=0
COYOTE_STEPS=4
BUFFER_STEPS=4
TEXT_CAP=8
PROPERTY_COUNT=16
STREAM_BYTES=13
CRC_POLY=7
.include "caller.inc"
.include "exercise.inc"
component_start:
.include "component.inc"
.include "data.inc"
.include "cases.inc"
code_end:
.segment "VECTORS"
.word nmi,reset,irq
.segment "CHARS"
.include "../../input/controller-reading/edges-font.inc"
.res 8192-272,0A client retaining state between calls
preview_rules:
.if CUSTOM
; SCORE = 255
lda #255
sta SCORE
; TAG = 4
lda #4
sta TAG
.if BROKEN
; SCORE = 0
lda #0
sta SCORE
.endif
jsr checked_step
jsr emit_state
; SCORE = 0
lda #0
sta SCORE
; TAG = 5
lda #5
sta TAG
.if BROKEN
; SCORE = 0
lda #0
sta SCORE
.endif
jsr checked_step
jsr emit_state
rts
.else
; SCORE = 20
lda #20
sta SCORE
; TAG = 1
lda #1
sta TAG
.if BROKEN
; SCORE = 0
lda #0
sta SCORE
.endif
jsr checked_step
jsr emit_state
; SCORE = 40
lda #40
sta SCORE
; TAG = 2
lda #2
sta TAG
.if BROKEN
; SCORE = 0
lda #0
sta SCORE
.endif
jsr checked_step
jsr emit_state
; SCORE = 40
lda #40
sta SCORE
; TAG = 3
lda #3
sta TAG
.if BROKEN
; SCORE = 0
lda #0
sta SCORE
.endif
jsr checked_step
jsr emit_state
.endif
rtsCustomise it
Retain the highest possible byte score and a zero score. The maintained custom caller changes its inputs or client sequence rather than hiding a different implementation behind the same label. Compare every state of the two clients, not only their final display.
Custom client selection
.segment "HEADER"
.byte "NES",$1a,2,1,0,0,0,0,0,0,0,0,0,0
RANK=$80
INSERTED=$81
VALID=$82
SCORE=$83
TAG=$84
COUNT=$85
S0=$86
S1=$87
S2=$88
S3=$89
I0=$8a
I1=$8b
I2=$8c
I3=$8d
T0=$8e
T1=$8f
T2=$90
T3=$91
EXPR_SAVE=$92
STATE=$80
input_ptr=$70
cases_left=$72
ptr=$74
saved_y=$76
OUTPUT=$0200
preview=OUTPUT+1400
ready=OUTPUT+1408
CUSTOM=1
BROKEN=0
COYOTE_STEPS=2
BUFFER_STEPS=2
TEXT_CAP=4
PROPERTY_COUNT=16
STREAM_BYTES=13
CRC_POLY=49
.include "caller.inc"
.include "exercise.inc"
component_start:
.include "component.inc"
.include "data.inc"
.include "cases.inc"
code_end:
.segment "VECTORS"
.word nmi,reset,irq
.segment "CHARS"
.include "../../input/controller-reading/edges-font.inc"
.res 8192-272,0The custom diagnostic row is 01 01 01 00 05 02 FF 00. The full client trace in the source explains how it gets there.
Mistake and repair
The wrong caller clears the achieved score before inserting it. The ordering routine cannot recover that lost value. Pass the completed score before resetting gameplay state.
The BROKEN branch lives in the sequential client, not the reusable helper. wrong.asm selects it; repaired.asm restores the normal call sequence. The repaired executable matches the normal program (for Spectrum, compare loaded CODE rather than the tape filename).
Select the deliberately wrong client
.segment "HEADER"
.byte "NES",$1a,2,1,0,0,0,0,0,0,0,0,0,0
RANK=$80
INSERTED=$81
VALID=$82
SCORE=$83
TAG=$84
COUNT=$85
S0=$86
S1=$87
S2=$88
S3=$89
I0=$8a
I1=$8b
I2=$8c
I3=$8d
T0=$8e
T1=$8f
T2=$90
T3=$91
EXPR_SAVE=$92
STATE=$80
input_ptr=$70
cases_left=$72
ptr=$74
saved_y=$76
OUTPUT=$0200
preview=OUTPUT+1400
ready=OUTPUT+1408
CUSTOM=0
BROKEN=1
COYOTE_STEPS=4
BUFFER_STEPS=4
TEXT_CAP=8
PROPERTY_COUNT=16
STREAM_BYTES=13
CRC_POLY=7
.include "caller.inc"
.include "exercise.inc"
component_start:
.include "component.inc"
.include "data.inc"
.include "cases.inc"
code_end:
.segment "VECTORS"
.word nmi,reset,irq
.segment "CHARS"
.include "../../input/controller-reading/edges-font.inc"
.res 8192-272,0
Cost and alternatives
The measured helper extent is 264 code bytes; public state is 14 bytes and private scratch is 5 bytes. There are no immutable helper tables. Caller data, the test cases, return-address stack, alignment and display buffers cost additional space. These are assembled sizes, not cycle measurements.
Four comparisons and at most three pair moves. Insertion is easier to audit than sorting the whole table after every result.
Scores are one byte and tags are identifiers, not name strings. Wider scores need a multi-byte comparison; permanent storage is a separate concern.
Execution evidence
Four variants run on NTSC NROM, background only, DMC/NMI disabled, using Asm198x 0.0.72, Emu198x 0.44.2. Each executes 64 boundary/varied/error table cases, dirty initialisation and the separate retained-state client. An independent mathematical/container model checks every public byte after every call. This is bounded example coverage, not exhaustive correctness for every possible state.
The records retain loaded immutable code, completion, register sentinels, full packets, source/tool/firmware hashes and captures. The public gate validates these retained observations and rejects altered evidence; it does not run restricted firmware. No firmware is distributed. The eight displayed bytes are the first eight public fields, zero-padded when shorter; the packet includes every field.
Where it fits
Score counters: Store the final score before starting a new run.