From 091944f534fa40952d04ed0d4fe738ef3848eb64 Mon Sep 17 00:00:00 2001
From: Esteban Diez Laiz <esteban.diezlaiz@gmail.com>
Date: Mon, 16 Aug 2021 21:45:17 +0200
Subject: [PATCH] ics2115: Improved sound using next-state logic

---
 src/devices/sound/ics2115.cpp | 49 +++++++++++++++++++++++++++++------
 1 file changed, 41 insertions(+), 8 deletions(-)

diff --git a/src/devices/sound/ics2115.cpp b/src/devices/sound/ics2115.cpp
index 868bcb70bc4..7f9ebd7cc0a 100644
--- a/src/devices/sound/ics2115.cpp
+++ b/src/devices/sound/ics2115.cpp
@@ -201,9 +201,31 @@ device_memory_interface::space_config_vector ics2115_device::memory_space_config
 }
 
 
-//TODO: improve using next-state logic from column 126 of patent 5809466
+// Using next-state logic from column 126 of patent 5809466.
+// VOL(L) = vol.acc
+// VINC = vol.inc
+// DIR = invert
+// BC = boundary cross (start or end )
+// BLEN = bi directional loop enable 
+// LEN loop enable 
+// UVOL  LEN   BLEN    DIR     BC      Next VOL(L)
+//  0      x     x       x       x       VOL(L) // no change no vol envelope
+//  1      x     x       0       0       VOL(L) + VINC // foward dir no bc 
+//  1      x     x       1       0       VOL(L) - VINC // invert no bc 
+//  1      0     x       x       1       VOL(L) // no env len no vel envelope
+// ----------------------------------------------------------------------------
+//  1      1     0       0       1       start - ( end - (VOL(L)  + VINC) ) 
+//  1      1     0       1       1       end + ( (VOL(L) - VINC) - start) 
+//  1      1     1       0       1       end + (end - (VOL(L) + VINC) ) // here
+//  1      1     1       1       1       start - ( (VOL(L) - VINC)- start)
 int ics2115_device::ics2115_voice::update_volume_envelope()
 {
+
+	// test for boundary cross
+	bool bc = false;
+	if (vol.acc >= vol.end || vol.acc <= vol.end)
+		bc = true;
+
 	int ret = 0;
 	if (vol_ctrl.bitflags.done || vol_ctrl.bitflags.stop)
 		return ret;
@@ -231,15 +253,26 @@ int ics2115_device::ics2115_voice::update_volume_envelope()
 	if (osc_conf.bitflags.eightbit)
 		return ret;
 
-	if (vol_ctrl.bitflags.loop)
+	if (vol_ctrl.bitflags.loop) 
 	{
-		if (vol_ctrl.bitflags.loop_bidir)
-			vol_ctrl.bitflags.invert = !vol_ctrl.bitflags.invert;
+		if (bc) {
+			if (!vol_ctrl.bitflags.loop_bidir && !vol_ctrl.bitflags.invert)
+				//  uvol = 1*     len = 1*   blen =  0     dir =  0     bc =  1*       start - ( end - (VOL(L)  + VINC) )
+				vol.acc = vol.start - (vol.end - (vol.acc + vol.incr));
 
-		if (vol_ctrl.bitflags.invert)
-			vol.acc = vol.end + vol.left;
-		else
-			vol.acc = vol.start - vol.left;
+			if (!vol_ctrl.bitflags.loop_bidir && vol_ctrl.bitflags.invert)
+				//  1      1     blen = 0      dir=   1       1       end + ( (VOL(L) - VINC) - start)
+				vol.acc = vol.end + ((vol.acc - vol.incr) - vol.start);
+
+			if (vol_ctrl.bitflags.loop_bidir && !vol_ctrl.bitflags.invert)
+				//  1      1     blen = 1      dir = 0       1       end + (end - (VOL(L) + VINC) )
+				vol.acc = vol.end + (vol.end - (vol.acc + vol.incr));
+
+
+			if (vol_ctrl.bitflags.loop_bidir && vol_ctrl.bitflags.invert)
+				//  1      1    beln =  1     dir =  1       1       start - ( (VOL(L) - VINC)- start)
+				vol.acc = vol.start - ((vol.acc - vol.incr) - vol.start);
+		}
 	}
 	else
 		vol_ctrl.bitflags.done = true;