Give an accepted action a sound. The same caller changes its picture and triggers this effect; a second version performs the action with the trigger removed. Listen to both.
Working effect
Trigger omitted
Take the effect
The reusable effect
; AY channel A; preserve mixer keyboard directions (port A output/B input).
trigger_sound:
push af
ld a,0
out ($02),a
ld a,100
out ($03),a
ld a,1
out ($02),a
xor a
out ($03),a
ld a,7
out ($02),a
ld a,$7e
out ($03),a
ld a,8
out ($02),a
ld a,15
out ($03),a
ld a,8
ld (SOUND_TICKS),a
pop af
ret
service_sound:
ld a,(SOUND_TICKS)
or a
ret z
dec a
ld (SOUND_TICKS),a
ret nz
ld a,8
out ($02),a
xor a
out ($03),a
retAY channel A, duration $8005. The routine sets mixer $7E, preserving the required port-A-output/port-B-input configuration. Trigger preserves AF/B; service changes AF. Both keyboard and sound share the AY address latch.
Include sound.inc once with the caller’s constants and duration byte. Initialise the duration byte to zero before the first service call. Call trigger_sound for an accepted action, then call service_sound exactly once per accepted display update. The eighth service call mutes the effect. Because the supplied caller services in the triggering iteration too, this is a count of service calls, not eight complete elapsed frame intervals. Triggering again restarts the duration; there is no queue.
The complete initialiser also mutes other channels. To reuse just this effect beside music, agree channel ownership and remove unrelated global setup only after providing a replacement. Device latches, power, routing and master volume may affect more than one voice.
Change it and recognise a mistake
Change tone A’s period/volume without changing keyboard port directions. A shared audio driver must coordinate with keyboard scanning.
The omitted-trigger control still accepts the action but fails the same audio guard as the working caller. Keyboard clicks or other machine output are not enough: the BASIC checks compare against a separate rejected-command recording.
Deliberately omitted sound trigger
; Original capability caller: owns VDP, one audio channel and declared RAM.
VDP_DATA equ $08
VDP_CTRL equ $09
TURNS equ $8000
SOUND_TICKS equ $8005
; Stock MOS disk boot header: destination, end, entry, disk mode.
org $9000
dw $9000,$9200,start
db 0
start:
di
ld sp,$fff0
xor a
ld ($8000),a
ld ($8001),a
ld ($8002),a
ld ($8003),a
ld a,1
out ($20),a ; mask dedicated keyboard interrupt
ld a,7
out ($02),a
ld a,$7f
out ($03),a ; mute tone/noise gates, port A output / B input
in a,($09)
xor a
out ($09),a
ld a,$80
out ($09),a ; R0 legacy graphics
xor a
out ($09),a
ld a,$81
out ($09),a ; R1 display and VDP IRQ disabled
call init_picture
main:
call wait_frame
ld hl,($8002)
inc hl
ld ($8002),hl
include "../sample.inc"
ld a,($8001)
cpl
and b
jr z,no_action
ld a,($8000)
inc a
ld ($8000),a
nop
nop
nop
no_action:
ld a,b
ld ($8001),a
call draw_picture
call service_sound
jp main
; AF clobbered; caller exclusively owns status/control-port latch.
wait_frame:
in a,($09)
wait_new:
in a,($09)
and $80
jr z,wait_new
ret
include "../picture.inc"
include "../sound.inc"
defs $9200-$,0The working implementation above repairs that omission. If an effect instead drones on, check the mute/service path and that its state is initialised. Servicing twice makes a counted effect shorter; servicing only after input can leave it running while the player waits. Those are lifecycle decisions to test when adapting it.
Run the caller
Build the complete caller with make -C tatung-einstein/patterns/assembly/input/read-action. Press Space once, keep it held, then release and press again. The piece moves on each new press and returns to its starting position after two; holding does not repeat the action. Attach build/demo.dsk and use Control-BREAK to let MOS boot it. This is a disk-boot program, not a CP/M or BASIC loader.
Where setup, trigger and service belong
; Original capability caller: owns VDP, one audio channel and declared RAM.
VDP_DATA equ $08
VDP_CTRL equ $09
TURNS equ $8000
SOUND_TICKS equ $8005
; Stock MOS disk boot header: destination, end, entry, disk mode.
org $9000
dw $9000,$9200,start
db 0
start:
di
ld sp,$fff0
xor a
ld ($8000),a
ld ($8001),a
ld ($8002),a
ld ($8003),a
ld a,1
out ($20),a ; mask dedicated keyboard interrupt
ld a,7
out ($02),a
ld a,$7f
out ($03),a ; mute tone/noise gates, port A output / B input
in a,($09)
xor a
out ($09),a
ld a,$80
out ($09),a ; R0 legacy graphics
xor a
out ($09),a
ld a,$81
out ($09),a ; R1 display and VDP IRQ disabled
call init_picture
main:
call wait_frame
ld hl,($8002)
inc hl
ld ($8002),hl
include "sample.inc"
ld a,($8001)
cpl
and b
jr z,no_action
ld a,($8000)
inc a
ld ($8000),a
call trigger_sound
no_action:
ld a,b
ld ($8001),a
call draw_picture
call service_sound
jp main
; AF clobbered; caller exclusively owns status/control-port latch.
wait_frame:
in a,($09)
wait_new:
in a,($09)
and $80
jr z,wait_new
ret
include "picture.inc"
include "sound.inc"
defs $9200-$,0Compare blocking, serviced and queued sound when choosing the next step.
Verification and sources
Target: TC-01 PAL, MOS 1.2, Ctrl-BREAK disk boot. These callers were executed with released Emu198x 0.44.1; assembly uses Asm198x 0.0.71. The sample folder contains reproduction instructions and retained observations. The independent checker binds source, native captures and actual output; its rejection tests exercise wrong state, missing files and false audio claims.
This qualifies the named emulator/firmware path. Pitch accuracy, original hardware and other peripherals require their own observations.
Tatung, Einstein Hardware Manual: programmable sound generator/keyboard interface and port decoding; MOS disk boot header; General Instrument AY-3-8910 data manual.