From 06f50ed77949cee495a1d8d98fec16648a5c8ea9 Mon Sep 17 00:00:00 2001
From: "Juan J. Martinez" <jjm@usebox.net>
Date: Mon, 15 May 2023 12:31:46 +0100
Subject: Added OPL3 support

---
 example.asm | 262 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 251 insertions(+), 11 deletions(-)

(limited to 'example.asm')

diff --git a/example.asm b/example.asm
index 992823f..468db3a 100644
--- a/example.asm
+++ b/example.asm
@@ -7,7 +7,8 @@
 .equ INT_VECT 0xff00
 
     ; setup an int handler so we
-    ; can use the frame int to sync
+    ; can use the frame interrupt to sync
+    ; and play sounds in background
     ld a, >INT_VECT
     ld x, <INT_VECT
     ld b, <int_handler
@@ -81,8 +82,10 @@ update_done:
     pop b
     jmp loop
 
-    ; make the sprite change direction
-    ; in: [a : x] inc*
+;
+; Make the sprite change direction and queue a sound
+;
+; in: [a : x] inc*
 turn:
     ;  1 -> -1
     ; -1 -> 1
@@ -96,11 +99,23 @@ turn:
     inc b
     and b, 15
     ld [sp + 2], b
-    ret
 
+    ; play an effect when we turn
+    ; alternating two sounds
+
+    ld x, <effect
+    ld a, >effect
+    ld y, [a : x]
+    xor y, 3
+    ld [a : x], y
+
+    call sound_queue_effect
+    ret
 
-    ; fill frame-buffer
-    ; in: reg b color
+;
+; fill frame-buffer
+;
+; in: reg b color
 fill_screen:
     ld a, 0xbf
     ld x, 0
@@ -116,11 +131,10 @@ fill_loop:
     jmp fill_loop
     ret
 
-int_handler:
-    iret
-
-    ; draw sprite
-    ; in: coordinates in px, py
+;
+; Draw the sprite
+;
+; in: coordinates in px, py
 draw_sprite:
     ; blitter in settings mode
     ld x, 128
@@ -167,3 +181,229 @@ incy:
 py:
     .db 64
 
+effect:
+    .db 1
+
+;
+; Our int handler plays / stops sounds
+;
+int_handler:
+    push a
+    push b
+    push x
+    push y
+    call sound_play
+    pop y
+    pop x
+    pop b
+    pop a
+    iret
+
+;
+; Queue a sound effect to be played
+;
+; in: y sound index (1 based)
+sound_queue_effect:
+    ; can't be interrupted
+    sif
+
+    ld a, >sound_efx
+    ld x, <sound_efx
+    dec y
+    ld b, y
+    add y, y
+    add y, b
+    add x, y
+    bo
+    inc a
+
+    ; effect addr
+    ld b, >sound_queue
+    ld y, <sound_queue
+    push x
+    ld x, [a : x]
+    ld [b : y], x
+    pop x
+    inc x
+    bo
+    inc a
+    inc y
+    bo
+    inc b
+    push x
+    ld x, [a : x]
+    ld [b : y], x
+    pop x
+
+    inc x
+    bo
+    inc a
+    ; x has length
+    ld x, [a : x]
+
+    ; current is 0
+    inc y
+    bo
+    inc b
+    ld a, 0
+    ld [b : y], a
+
+    ; length
+    inc y
+    bo
+    inc b
+    ld [b : y], x
+
+    cif
+    ret
+
+;
+; Plays sound in our queue
+;
+; To be run from the interrupt handler. Can't play effects which data is at 0x0000.
+; It is very simple and uses only channel 0.
+;
+sound_play:
+    ld b, >sound_queue
+    ld y, <sound_queue
+
+    ; check we have a valid addr in the queue (not 0x0000)
+    ld x, [b : y]
+    inc y
+    bo
+    inc b
+    ld a, [b : y]
+    cmp a, 0
+    bnz
+    jmp sound_play_has_addr
+    cmp x, 0
+    bz
+    ret
+
+sound_play_has_addr:
+    push a
+
+    inc y
+    bo
+    inc b
+
+    ; is already playing?
+    ld a, [b : y]
+    cmp a, 0
+    bz
+    jmp sound_play_start
+
+    ; the sound is active
+    pop a
+    ld a, [b : y]
+
+    ; another frame
+    inc a
+    ld [b : y], a
+
+    inc y
+    bo
+    inc b
+
+    ; is the end?
+    ld x, [b : y]
+    cmp x, a
+    bnc
+    ret
+
+    ; no active sound now: set addr to 0x0000
+    ld b, >sound_queue
+    ld y, <sound_queue
+    ld x, 0
+    ld [b : y], x
+    inc y
+    bo
+    inc b
+    ld [b : y], x
+
+    ; stop the sound
+    ld b, 0xc0
+    ld y, 0xb0
+    port b, y
+
+    ld b, 0xc1
+    ld y, 0x11
+    port b, y
+    ret
+
+sound_play_start:
+    ; we start playing
+    inc a
+    ld [b : y], a
+
+    pop a
+    ; a : x has the effect addr
+
+sound_loop:
+    ld y, [a : x]
+    cmp y, 0xff
+    bz
+    ret
+
+    ld b, 0xc0
+    port b, y
+
+    inc x
+    bo
+    inc a
+
+    ld y, [a : x]
+
+    ld b, 0xc1
+    port b, y
+
+    inc x
+    bo
+    inc a
+
+    jmp sound_loop
+
+sound_queue:
+    ; effect addr, current frame count, length
+    .ds 4, 0
+
+sound_efx:
+    ; addr to the instrument data
+    .dw sound_efx_data0
+    ; length in frames
+    .db 2
+    .dw sound_efx_data1
+    .db 2
+
+sound_efx_data0:
+    ; register, value
+    .db 0x20, 0x01
+    .db 0x40, 0x10
+    .db 0x60, 0xF0
+    .db 0x80, 0x77
+    .db 0xA0, 0x81
+    .db 0x23, 0x01
+    .db 0x43, 0x00
+    .db 0x63, 0xF0
+    .db 0x83, 0x77
+    .db 0xe0, 0x03
+    .db 0xB0, 0x31
+    ; end of sequence marker
+    .db 0xff
+
+sound_efx_data1:
+    ; register, value
+    .db 0x20, 0x01
+    .db 0x40, 0x10
+    .db 0x60, 0xF0
+    .db 0x80, 0x77
+    .db 0xA0, 0xb0
+    .db 0x23, 0x01
+    .db 0x43, 0x00
+    .db 0x63, 0xF0
+    .db 0x83, 0x77
+    .db 0xe0, 0x03
+    .db 0xB0, 0x31
+    ; end of sequence marker
+    .db 0xff
+
-- 
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