From fa4890c9db396b03b5f8186bad6c92892fd2d92a Mon Sep 17 00:00:00 2001
From: OBattler <oubattler@gmail.com>
Date: Mon, 11 Nov 2019 06:07:50 +0100
Subject: [PATCH] Some fixes to the PC speaker - fixes amplitude in mode 1 (the
 intro of Perestroika now works correctly at least on the 8088 4.77 MHz) and
 makes the parameters consistent with the rest of the PC speaker emulation.

---
 src/sound/snd_speaker.c | 37 +++++++++++++++++++++++++++++++++----
 1 file changed, 33 insertions(+), 4 deletions(-)

diff --git a/src/sound/snd_speaker.c b/src/sound/snd_speaker.c
index 9c40d5e89..799614fea 100644
--- a/src/sound/snd_speaker.c
+++ b/src/sound/snd_speaker.c
@@ -1,3 +1,21 @@
+/*
+ * 86Box	A hypervisor and IBM PC system emulator that specializes in
+ *		running old operating systems and software designed for IBM
+ *		PC systems and compatibles from 1981 through fairly recent
+ *		system designs based on the PCI bus.
+ *
+ *		This file is part of the 86Box distribution.
+ *
+ *		Emulation of the PC speaker.
+ *
+ * Version:	@(#)snd_speaker.c	1.0.0	2019/11/11
+ *
+ * Authors:	Sarah Walker, <http://pcem-emulator.co.uk/>
+ *		Miran Grca, <mgrca8@gmail.com>
+ *
+ *		Copyright 2008-2019 Sarah Walker.
+ *		Copyright 2016-2019 Miran Grca.
+ */
 #include <stdio.h>
 #include <stdint.h>
 #include <string.h>
@@ -23,20 +41,31 @@ void
 speaker_update(void)
 {
     int32_t val;
+    double timer2_count, amplitude;
+
+    timer2_count = pit.l[2] ? ((double) pit.l[2]) : 65536.0;
+    amplitude = ((timer2_count / 64.0) * 10240.0) - 5120.0;
+
+    if (amplitude > 5120.0)
+	amplitude = 5120.0;
 
     if (speaker_pos >= sound_pos_global)
 	return;
 
     for (; speaker_pos < sound_pos_global; speaker_pos++) {
 	if (speaker_gated && was_speaker_enable) {
-		if (!pit.m[2] || pit.m[2]==4)
-			val = speakval;
+		if ((pit.m[2] == 0) || (pit.m[2] == 4))
+			val = (int32_t) amplitude;
 		else if (pit.l[2] < 0x40)
 			val = 0xa00;
 		else
 			val = speakon ? 0x1400 : 0;
-	} else
-		val = was_speaker_enable ? 0x1400 : 0;
+	} else {
+		if (pit.m[2] == 1)
+			val = was_speaker_enable ? (int32_t) amplitude : 0;
+		else
+			val = was_speaker_enable ? 0x1400 : 0;
+	}
 
 	if (!speaker_enable)
 		was_speaker_enable = 0;