From c33ec6922fec2f7b64714f2e934c4aac15160a26 Mon Sep 17 00:00:00 2001
From: angelosa <lordkale4@gmail.com>
Date: Wed, 1 May 2024 22:40:16 +0200
Subject: [PATCH] machine/z80ctc.cpp: fix channel bus readback on unset timer *
 fix x1turbo not detecting YM regression caused by
 293fb66d7f56897f587721254e47d855241d514d

---
 src/devices/machine/z80ctc.cpp | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/devices/machine/z80ctc.cpp b/src/devices/machine/z80ctc.cpp
index 7f0049b28e8..b5d87818985 100644
--- a/src/devices/machine/z80ctc.cpp
+++ b/src/devices/machine/z80ctc.cpp
@@ -368,7 +368,11 @@ u8 z80ctc_channel_device::read()
 		if(!m_timer->remaining().is_never())
 			return u8((m_timer->remaining().as_double() / period.as_double()) + 1.0);
 		else
-			return 0;
+        {
+            // value read-back is required by x1turbo for YM internal board detection.
+            // cfr. x1turbo40 argus wpiset 0x704,1,rw
+			return m_down;
+        }
 	}
 }