A poison effect needs a duration and a pulse interval, not a fresh timer every time the actor is updated.
Use it in a project
PERIOD must be nonzero and PHASE below it. APPLY nonzero refreshes REMAINING from DURATION and restarts phase. The same service call consumes the first active tick. Each active tick advances PHASE, emitting PULSE=1 on a period boundary. Expiration clears PHASE; a pulse on the final active tick is allowed. Invalid configuration returns VALID=0 and PULSE=0 without changing timer state.
Include component.inc once (MOS callers include the shared 6502 implementation through it). Reserve the public fields in this exact order: PULSE, REMAINING, PHASE, DURATION, PERIOD, APPLY, VALID. They occupy 7 contiguous bytes. Also reserve the private workspace: none (0 bytes). Array names in the explanation refer to the numbered consecutive bindings, such as C0, C1 and so on.
Call timed_status_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 timed_status_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 | REMAINING and PHASE |
| Supply before service | DURATION, PERIOD and APPLY |
| Read after service | PULSE and VALID |
Duration bounds the lifetime while phase measures progress within a pulse interval. Keeping those clocks separate avoids making the last partial interval extend the effect forever.
Reusable initialisation and service
; SPDX-License-Identifier: MIT
; Service a Timed Status Effect. See README.md for the byte interface and ownership.
; init clears the public fields and private workspace; set inputs afterwards.
timed_status_init:
move.b #0,d0
move.b d0,PULSE
move.b d0,REMAINING
move.b d0,PHASE
move.b d0,DURATION
move.b d0,PERIOD
move.b d0,APPLY
move.b d0,VALID
rts
timed_status_step:
; PULSE = 0
move.b #0,d0
move.b d0,PULSE
; VALID = 0
move.b #0,d0
move.b d0,VALID
; if PERIOD == 0:
move.b PERIOD,d0
cmp.b #0,d0
beq timed_status_L1
jmp timed_status_L2
timed_status_L1:
; return
rts
jmp timed_status_L3
timed_status_L2:
timed_status_L3:
; if PHASE >= PERIOD:
move.b PHASE,d0
move.b PERIOD,d1
cmp.b d1,d0
bcc timed_status_L4
jmp timed_status_L5
timed_status_L4:
; return
rts
jmp timed_status_L6
timed_status_L5:
timed_status_L6:
; VALID = 1
move.b #1,d0
move.b d0,VALID
; if APPLY != 0:
move.b APPLY,d0
cmp.b #0,d0
bne timed_status_L7
jmp timed_status_L8
timed_status_L7:
; REMAINING = DURATION
move.b DURATION,d0
move.b d0,REMAINING
; PHASE = 0
move.b #0,d0
move.b d0,PHASE
jmp timed_status_L9
timed_status_L8:
timed_status_L9:
; if REMAINING == 0:
move.b REMAINING,d0
cmp.b #0,d0
beq timed_status_L10
jmp timed_status_L11
timed_status_L10:
; PHASE = 0
move.b #0,d0
move.b d0,PHASE
; return
rts
jmp timed_status_L12
timed_status_L11:
timed_status_L12:
; REMAINING = REMAINING - 1
move.b REMAINING,d0
sub.b #1,d0
move.b d0,REMAINING
; PHASE = PHASE + 1
move.b PHASE,d0
add.b #1,d0
move.b d0,PHASE
; if PHASE == PERIOD:
move.b PHASE,d0
move.b PERIOD,d1
cmp.b d1,d0
beq timed_status_L13
jmp timed_status_L14
timed_status_L13:
; PHASE = 0
move.b #0,d0
move.b d0,PHASE
; PULSE = 1
move.b #1,d0
move.b d0,PULSE
jmp timed_status_L15
timed_status_L14:
timed_status_L15:
; if REMAINING == 0:
move.b REMAINING,d0
cmp.b #0,d0
beq timed_status_L16
jmp timed_status_L17
timed_status_L16:
; PHASE = 0
move.b #0,d0
move.b d0,PHASE
jmp timed_status_L18
timed_status_L17:
timed_status_L18:
rts
component_end:Machine contract
D0–D3/A0–A1/CCR may change; D4–D7/A2–A6 are preserved. A direct BSR/JSR needs four 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 A500 OCS diagnostic cold-boots an OFS disk, owns the Copper and bitplane and disables interrupt/DMA sources. The helper does not take over hardware or allocate Chip RAM.
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 and BUILD198X=/path/to/build198x. The Makefile produces normal, custom, deliberately wrong and repaired programs. Tools must already be installed; the sample downloads nothing.
Bindings and include order
section code,code_c
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"
even
include "data.inc"
include "cases.inc"
even
include "display.inc"
include "../../framework/turn-deadline/font.inc"
code_end:
STATE:
PULSE: dc.b 0
REMAINING: dc.b 0
PHASE: dc.b 0
DURATION: dc.b 0
PERIOD: dc.b 0
APPLY: dc.b 0
VALID: dc.b 0
even
ready: dc.w 0
preview: dcb.b 8,0
OUTPUT: dcb.b 1300,0
even
signature: dc.b "198XWORLDKIT000",0
even
copperlist:
dc.w $08e,$2c81,$090,$2cc1,$092,$0038,$094,$00d0
dc.w $100,$1200,$102,0,$104,0,$108,0,$10a,0
dc.w $180,$012,$182,$fff
copbpl:
dc.w $0e0,0,$0e2,0
dc.w $ffff,$fffe
plane: dcb.b 10240,0A client retaining state between calls
preview_rules:
ifne CUSTOM
; DURATION = 6
move.b #6,d0
move.b d0,DURATION
; PERIOD = 3
move.b #3,d0
move.b d0,PERIOD
; APPLY = 1
move.b #1,d0
move.b d0,APPLY
ifne BROKEN
; APPLY = 1
move.b #1,d0
move.b d0,APPLY
endif
bsr checked_step
bsr emit_state
; APPLY = 0
move.b #0,d0
move.b d0,APPLY
ifne BROKEN
; APPLY = 1
move.b #1,d0
move.b d0,APPLY
endif
bsr checked_step
bsr emit_state
ifne BROKEN
; APPLY = 1
move.b #1,d0
move.b d0,APPLY
endif
bsr checked_step
bsr emit_state
ifne BROKEN
; APPLY = 1
move.b #1,d0
move.b d0,APPLY
endif
bsr checked_step
bsr emit_state
ifne BROKEN
; APPLY = 1
move.b #1,d0
move.b d0,APPLY
endif
bsr checked_step
bsr emit_state
ifne BROKEN
; APPLY = 1
move.b #1,d0
move.b d0,APPLY
endif
bsr checked_step
bsr emit_state
rts
else
; DURATION = 5
move.b #5,d0
move.b d0,DURATION
; PERIOD = 2
move.b #2,d0
move.b d0,PERIOD
; APPLY = 1
move.b #1,d0
move.b d0,APPLY
ifne BROKEN
; APPLY = 1
move.b #1,d0
move.b d0,APPLY
endif
bsr checked_step
bsr emit_state
; APPLY = 0
move.b #0,d0
move.b d0,APPLY
ifne BROKEN
; APPLY = 1
move.b #1,d0
move.b d0,APPLY
endif
bsr checked_step
bsr emit_state
ifne BROKEN
; APPLY = 1
move.b #1,d0
move.b d0,APPLY
endif
bsr checked_step
bsr emit_state
ifne BROKEN
; APPLY = 1
move.b #1,d0
move.b d0,APPLY
endif
bsr checked_step
bsr emit_state
ifne BROKEN
; APPLY = 1
move.b #1,d0
move.b d0,APPLY
endif
bsr checked_step
bsr emit_state
endif
rtsCustomise it
Use a six-tick duration with one pulse every three ticks. 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
section code,code_c
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"
even
include "data.inc"
include "cases.inc"
even
include "display.inc"
include "../../framework/turn-deadline/font.inc"
code_end:
STATE:
PULSE: dc.b 0
REMAINING: dc.b 0
PHASE: dc.b 0
DURATION: dc.b 0
PERIOD: dc.b 0
APPLY: dc.b 0
VALID: dc.b 0
even
ready: dc.w 0
preview: dcb.b 8,0
OUTPUT: dcb.b 1300,0
even
signature: dc.b "198XWORLDKIT000",0
even
copperlist:
dc.w $08e,$2c81,$090,$2cc1,$092,$0038,$094,$00d0
dc.w $100,$1200,$102,0,$104,0,$108,0,$10a,0
dc.w $180,$012,$182,$fff
copbpl:
dc.w $0e0,0,$0e2,0
dc.w $ffff,$fffe
plane: dcb.b 10240,0The custom diagnostic row is 01 00 00 06 03 00 01 00. The full client trace in the source explains how it gets there.
Mistake and repair
The wrong caller keeps APPLY set. Every call refreshes the effect and restarts its interval, preventing the expected pulses and expiry. Feed an application event once, then service retained 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
section code,code_c
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"
even
include "data.inc"
include "cases.inc"
even
include "display.inc"
include "../../framework/turn-deadline/font.inc"
code_end:
STATE:
PULSE: dc.b 0
REMAINING: dc.b 0
PHASE: dc.b 0
DURATION: dc.b 0
PERIOD: dc.b 0
APPLY: dc.b 0
VALID: dc.b 0
even
ready: dc.w 0
preview: dcb.b 8,0
OUTPUT: dcb.b 1300,0
even
signature: dc.b "198XWORLDKIT000",0
even
copperlist:
dc.w $08e,$2c81,$090,$2cc1,$092,$0038,$094,$00d0
dc.w $100,$1200,$102,0,$104,0,$108,0,$10a,0
dc.w $180,$012,$182,$fff
copbpl:
dc.w $0e0,0,$0e2,0
dc.w $ffff,$fffe
plane: dcb.b 10240,0
Cost and alternatives
The measured helper extent is 274 code bytes; public state is 7 bytes and private scratch is 0 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.
Constant work per service. Multiple independent effects need separate state or a bounded effect table; sharing one timer silently merges their lifetimes.
PULSE is an event; a damage routine decides what it means for health and invulnerability. This stores only one effect instance and refreshes rather than stacks it. A paused game must choose whether to service the effect.
Execution evidence
Four variants run on A500 OCS PAL, Kickstart1.3 OFS cold boot, using Asm198x 0.0.72, Emu198x 0.44.2 and Build198x 0.2.9. 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
Damage rules: A periodic pulse can request damage without taking ownership of health or its protection policy.