A reused pool slot should not let an old reference suddenly name a different enemy.
Use it in a project
Four slots use ACTIVE bits 0–3 and one generation byte each. MODE=0 allocates the lowest free slot and increments its generation modulo 256. MODE=1 frees a live SLOT with matching GENERATION; MODE=2 queries that handle. RESULT=1 returns OUT_SLOT/OUT_GENERATION; failure returns 255/0. ACTIVE above 15, unknown mode or out-of-range handle index returns VALID=0; ordinary full/stale requests are valid failures.
Include component.inc once (MOS callers include the shared 6502 implementation through it). Reserve the public fields in this exact order: RESULT, OUT_SLOT, OUT_GENERATION, VALID, MODE, SLOT, GENERATION, ACTIVE, G0, G1, G2, G3. They occupy 12 contiguous bytes. Also reserve the private workspace: T0, T1, T2, EXPR_SAVE (4 bytes). Array names in the explanation refer to the numbered consecutive bindings, such as C0, C1 and so on.
Call generation_handles_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 generation_handles_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 | ACTIVE and G0–G3 |
| Supply before service | MODE, SLOT and GENERATION |
| Read after service | RESULT, OUT_SLOT, OUT_GENERATION and VALID |
An index says where storage is; a generation says which lifetime occupies it. Releasing clears the live bit, while allocating advances the lifetime before returning a new reference.
Reusable initialisation and service
; SPDX-License-Identifier: MIT
; Reject Stale Object Handles. See README.md for the byte interface and ownership.
; init clears the public fields and private workspace; set inputs afterwards.
generation_handles_init:
lda #0
sta RESULT
sta OUT_SLOT
sta OUT_GENERATION
sta VALID
sta MODE
sta SLOT
sta GENERATION
sta ACTIVE
sta G0
sta G1
sta G2
sta G3
sta T0
sta T1
sta T2
sta EXPR_SAVE
rts
generation_handles_step:
; RESULT = 0
lda #0
sta RESULT
; OUT_SLOT = 255
lda #255
sta OUT_SLOT
; OUT_GENERATION = 0
lda #0
sta OUT_GENERATION
; VALID = 0
lda #0
sta VALID
; if ACTIVE > 15:
lda ACTIVE
cmp #15
beq generation_handles_L5
bcs generation_handles_L4
generation_handles_L5:
jmp generation_handles_L2
generation_handles_L4:
jmp generation_handles_L1
generation_handles_L1:
; return
rts
jmp generation_handles_L3
generation_handles_L2:
generation_handles_L3:
; if MODE >= 3:
lda MODE
cmp #3
bcs generation_handles_L9
generation_handles_L10:
jmp generation_handles_L7
generation_handles_L9:
jmp generation_handles_L6
generation_handles_L6:
; return
rts
jmp generation_handles_L8
generation_handles_L7:
generation_handles_L8:
; if MODE == 0:
lda MODE
cmp #0
beq generation_handles_L14
generation_handles_L15:
jmp generation_handles_L12
generation_handles_L14:
jmp generation_handles_L11
generation_handles_L11:
; VALID = 1
lda #1
sta VALID
; T0 = 0
lda #0
sta T0
; T1 = 1
lda #1
sta T1
; while T0 < 4:
generation_handles_L16:
lda T0
cmp #4
bcc generation_handles_L19
generation_handles_L20:
jmp generation_handles_L18
generation_handles_L19:
jmp generation_handles_L17
generation_handles_L17:
; T2 = ACTIVE & T1
lda ACTIVE
and T1
sta T2
; if T2 == 0:
lda T2
cmp #0
beq generation_handles_L24
generation_handles_L25:
jmp generation_handles_L22
generation_handles_L24:
jmp generation_handles_L21
generation_handles_L21:
; T2 = G[T0]
ldx T0
lda G0,x
sta T2
; T2 = T2 + 1
lda T2
clc
adc #1
sta T2
; G[T0] = T2
lda T2
sta EXPR_SAVE
ldx T0
lda EXPR_SAVE
sta G0,x
; ACTIVE = ACTIVE | T1
lda ACTIVE
ora T1
sta ACTIVE
; OUT_SLOT = T0
lda T0
sta OUT_SLOT
; OUT_GENERATION = T2
lda T2
sta OUT_GENERATION
; RESULT = 1
lda #1
sta RESULT
; return
rts
jmp generation_handles_L23
generation_handles_L22:
generation_handles_L23:
; T0 = T0 + 1
lda T0
clc
adc #1
sta T0
; T1 = T1 << 1
lda T1
asl
sta T1
jmp generation_handles_L16
generation_handles_L18:
; return
rts
jmp generation_handles_L13
generation_handles_L12:
generation_handles_L13:
; if SLOT >= 4:
lda SLOT
cmp #4
bcs generation_handles_L29
generation_handles_L30:
jmp generation_handles_L27
generation_handles_L29:
jmp generation_handles_L26
generation_handles_L26:
; return
rts
jmp generation_handles_L28
generation_handles_L27:
generation_handles_L28:
; VALID = 1
lda #1
sta VALID
; T0 = 1
lda #1
sta T0
; T1 = SLOT
lda SLOT
sta T1
; while T1 != 0:
generation_handles_L31:
lda T1
cmp #0
bne generation_handles_L34
generation_handles_L35:
jmp generation_handles_L33
generation_handles_L34:
jmp generation_handles_L32
generation_handles_L32:
; T0 = T0 << 1
lda T0
asl
sta T0
; T1 = T1 - 1
lda T1
sec
sbc #1
sta T1
jmp generation_handles_L31
generation_handles_L33:
; T1 = ACTIVE & T0
lda ACTIVE
and T0
sta T1
; if T1 == 0:
lda T1
cmp #0
beq generation_handles_L39
generation_handles_L40:
jmp generation_handles_L37
generation_handles_L39:
jmp generation_handles_L36
generation_handles_L36:
; return
rts
jmp generation_handles_L38
generation_handles_L37:
generation_handles_L38:
; T1 = G[SLOT]
ldx SLOT
lda G0,x
sta T1
; if T1 != GENERATION:
lda T1
cmp GENERATION
bne generation_handles_L44
generation_handles_L45:
jmp generation_handles_L42
generation_handles_L44:
jmp generation_handles_L41
generation_handles_L41:
; return
rts
jmp generation_handles_L43
generation_handles_L42:
generation_handles_L43:
; OUT_SLOT = SLOT
lda SLOT
sta OUT_SLOT
; OUT_GENERATION = T1
lda T1
sta OUT_GENERATION
; RESULT = 1
lda #1
sta RESULT
; if MODE == 1:
lda MODE
cmp #1
beq generation_handles_L49
generation_handles_L50:
jmp generation_handles_L47
generation_handles_L49:
jmp generation_handles_L46
generation_handles_L46:
; T0 = T0 ^ 255
lda T0
eor #255
sta T0
; ACTIVE = ACTIVE & T0
lda ACTIVE
and T0
sta ACTIVE
jmp generation_handles_L48
generation_handles_L47:
generation_handles_L48:
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
RESULT=$80
OUT_SLOT=$81
OUT_GENERATION=$82
VALID=$83
MODE=$84
SLOT=$85
GENERATION=$86
ACTIVE=$87
G0=$88
G1=$89
G2=$8a
G3=$8b
T0=$8c
T1=$8d
T2=$8e
EXPR_SAVE=$8f
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
; G0 = 255
lda #255
sta G0
.if BROKEN
; GENERATION = 0
lda #0
sta GENERATION
.endif
jsr checked_step
jsr emit_state
; MODE = 2
lda #2
sta MODE
; SLOT = 0
lda #0
sta SLOT
; GENERATION = 0
lda #0
sta GENERATION
.if BROKEN
; GENERATION = 0
lda #0
sta GENERATION
.endif
jsr checked_step
jsr emit_state
rts
.else
.if BROKEN
; GENERATION = 0
lda #0
sta GENERATION
.endif
jsr checked_step
jsr emit_state
; MODE = 1
lda #1
sta MODE
; SLOT = 0
lda #0
sta SLOT
; GENERATION = 1
lda #1
sta GENERATION
.if BROKEN
; GENERATION = 0
lda #0
sta GENERATION
.endif
jsr checked_step
jsr emit_state
; MODE = 0
lda #0
sta MODE
.if BROKEN
; GENERATION = 0
lda #0
sta GENERATION
.endif
jsr checked_step
jsr emit_state
; MODE = 2
lda #2
sta MODE
; SLOT = 0
lda #0
sta SLOT
; GENERATION = 2
lda #2
sta GENERATION
.if BROKEN
; GENERATION = 0
lda #0
sta GENERATION
.endif
jsr checked_step
jsr emit_state
.endif
rtsCustomise it
Exercise a generation-byte wrap from 255 to zero. 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
RESULT=$80
OUT_SLOT=$81
OUT_GENERATION=$82
VALID=$83
MODE=$84
SLOT=$85
GENERATION=$86
ACTIVE=$87
G0=$88
G1=$89
G2=$8a
G3=$8b
T0=$8c
T1=$8d
T2=$8e
EXPR_SAVE=$8f
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 00 00 01 02 00 00 01. The full client trace in the source explains how it gets there.
Mistake and repair
The wrong caller throws away the generation part of each reference. Free/query requests fail or eventually identify the wrong lifetime. Store and pass both parts of the returned handle.
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
RESULT=$80
OUT_SLOT=$81
OUT_GENERATION=$82
VALID=$83
MODE=$84
SLOT=$85
GENERATION=$86
ACTIVE=$87
G0=$88
G1=$89
G2=$8a
G3=$8b
T0=$8c
T1=$8d
T2=$8e
EXPR_SAVE=$8f
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 342 code bytes; public state is 12 bytes and private scratch is 4 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.
Allocation scans at most four slots; validated query/free uses at most three mask shifts. Stable indices avoid moving object records, at the cost of live flags and generation storage.
A byte generation eventually wraps: a sufficiently old handle can alias after 256 allocations of that slot. Wider generations reduce that risk but do not create eternal uniqueness. This validates identity, not object type, ownership or thread safety.
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
Object pools: Generation handles extend slot reuse with identity checks; they do not replace the pool’s actual object storage.