From 4bdac7404ad8e43ac953c6a94af4a8a27ce225f1 Mon Sep 17 00:00:00 2001
From: Irmen de Jong <irmen@razorvine.net>
Date: Sun, 3 Jul 2022 00:55:25 +0200
Subject: [PATCH] added sustain to psg envelope

---
 compiler/res/prog8lib/cx16/psg.p8 | 14 ++++++++++++--
 examples/cx16/bdmusic.p8          |  8 ++++----
 2 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/compiler/res/prog8lib/cx16/psg.p8 b/compiler/res/prog8lib/cx16/psg.p8
index 3136381af..346908bb6 100644
--- a/compiler/res/prog8lib/cx16/psg.p8
+++ b/compiler/res/prog8lib/cx16/psg.p8
@@ -41,9 +41,10 @@ psg {
         cx16.vpoke(1, reg, cx16.vpeek(1, reg) & %11000000 | pw)
     }
 
-    sub envelope(ubyte voice_num, ubyte attack, ubyte release) {
+    sub envelope(ubyte voice_num, ubyte attack, ubyte sustain, ubyte release) {
         envelope_states[voice_num] = 255
         envelope_attacks[voice_num] = attack * $0040
+        envelope_sustains[voice_num] = sustain
         envelope_releases[voice_num] = release * $0040
         if attack
             attack = 0
@@ -75,11 +76,19 @@ psg {
                     if msb(cx16.r0) & %11000000 or envelope_attacks[cx16.r15L]==0 {
                         cx16.r0 = mkword(63, 0)
                         envelope_attacks[cx16.r15L] = 0
-                        envelope_states[cx16.r15L] = 1  ; start release
+                        envelope_states[cx16.r15L] = 1  ; start sustain
                     }
                     envelope_volumes[cx16.r15L] = cx16.r0
                 }
                 1 -> {
+                    ; sustain
+                    if envelope_sustains[cx16.r15L] {
+                        envelope_sustains[cx16.r15L]--
+                    } else {
+                        envelope_states[cx16.r15L] = 2  ; start release
+                    }
+                }
+                2 -> {
                     ; release
                     cx16.r0 = envelope_volumes[cx16.r15L] - envelope_releases[cx16.r15L]
                     if msb(cx16.r0) & %11000000 {
@@ -110,5 +119,6 @@ psg {
     ubyte[16] envelope_states
     uword[16] envelope_volumes
     uword[16] envelope_attacks
+    ubyte[16] envelope_sustains
     uword[16] envelope_releases
 }
diff --git a/examples/cx16/bdmusic.p8 b/examples/cx16/bdmusic.p8
index 752dd84b1..e2a4fc9f5 100644
--- a/examples/cx16/bdmusic.p8
+++ b/examples/cx16/bdmusic.p8
@@ -12,8 +12,8 @@ main {
         psg.voice(1, psg.RIGHT, 0, psg.NOISE, 0)
         psg.freq(0, 1000)
         psg.freq(1, 2000)
-        psg.envelope(0, 50, 5)
-        psg.envelope(1, 80, 6)
+        psg.envelope(0, 50, 0, 5)
+        psg.envelope(1, 80, 0, 6)
         sys.wait(100)
         psg.silent()
         cx16.restore_irq()
@@ -68,8 +68,8 @@ main {
                 ubyte note1 = msb(note)
                 psg.freq(0, vera_freqs[note0])
                 psg.freq(1, vera_freqs[note1])
-                psg.envelope(0, 255, 6)
-                psg.envelope(1, 255, 6)
+                psg.envelope(0, 255, 0, 6)
+                psg.envelope(1, 255, 0, 6)
                 print_notes(note0, note1)
                 sys.wait(10)
             }