From 2ba3fe29c12d79aa67e9b71a516acf9175b78464 Mon Sep 17 00:00:00 2001
From: wilbertpol <wilbertpol@users.noreply.github.com>
Date: Mon, 28 Oct 2024 15:29:47 +0000
Subject: [PATCH] sound/upd1771.cpp: Improve check for end of adpcm stream when
 the stream contains multiple samples. (#12913)

* Fixes SCV Star Speeder.
---
 src/devices/sound/upd1771.cpp | 29 ++++++++++++++++++++++-------
 1 file changed, 22 insertions(+), 7 deletions(-)

diff --git a/src/devices/sound/upd1771.cpp b/src/devices/sound/upd1771.cpp
index 6b0ef06b884..b08ced8779f 100644
--- a/src/devices/sound/upd1771.cpp
+++ b/src/devices/sound/upd1771.cpp
@@ -432,15 +432,30 @@ void upd1771c_device::write(uint8_t data)
 			//6Khz(ish) DIGI playback
 
 			//end capture
-			if (m_index >= 2 && m_packet[m_index - 2] == 0xfe && m_packet[m_index - 1] == 0x00)
 			{
-				//TODO play capture!
-				m_index = 0;
-				m_packet[0] = 0;
-				m_state = STATE_ADPCM;
+				bool have_all_data = false;
+				if (m_index >= 2 && m_packet[m_index - 2] == 0xfe && m_packet[m_index - 1] == 0x00)
+				{
+					//TODO play capture!
+					if (m_index >= 6)
+					{
+						// offsets 2 and 3 in the transferred pcm data seem to contain the number of samples
+						uint16_t count = (m_packet[4] << 8) | m_packet[3];
+						count--;
+						m_packet[3] = count & 0xff;
+						m_packet[4] = (count >> 8);
+						if (count == 0)
+						{
+							m_index = 0;
+							m_packet[0] = 0;
+							m_state = STATE_ADPCM;
+							have_all_data = true;
+						}
+					}
+				}
+				if (!have_all_data)
+					m_timer->adjust(attotime::from_ticks(512, clock()));
 			}
-			else
-				m_timer->adjust(attotime::from_ticks(512, clock()));
 			break;
 
 		//garbage: wipe stack