From f38b72ea7d21405eabb51cdf53fc31296c558e3a Mon Sep 17 00:00:00 2001
From: "R. Belmont" <rb6502@users.noreply.github.com>
Date: Mon, 13 Oct 2014 20:04:05 +0000
Subject: [PATCH] (MESS) osdcore: reject invalid MIDI bytes with no status,
 fixes most 6850-based MIDI setups. [R. Belmont]

---
 src/osd/osdcore.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/osd/osdcore.c b/src/osd/osdcore.c
index e965272052e..8207595d158 100644
--- a/src/osd/osdcore.c
+++ b/src/osd/osdcore.c
@@ -470,6 +470,13 @@ void osd_write_midi_channel(osd_midi_device *dev, UINT8 data)
 
 //  printf("write: %02x (%d)\n", data, dev->xmit_cnt);
 
+	// reject data bytes when no valid status exists
+	if ((dev->last_status == 0) && !(data & 0x80))
+	{
+		dev->xmit_cnt = 0;
+		return;
+	}
+
 	if (dev->xmit_cnt >= 4)
 	{
 		printf("MIDI out: packet assembly overflow, contact MAMEdev!\n");