From dde3e0c50d6b4f975752b81a8fb0520239ce852b Mon Sep 17 00:00:00 2001
From: MetalliC <0vetal0@gmail.com>
Date: Thu, 28 May 2015 15:49:30 +0300
Subject: [PATCH] beta128: patch some TR-DOS bug so Pentagon and Scorpion works
 ok with FDD until wd_fdc cant handle this (nw)

---
 src/mess/drivers/scorpion.c |  2 ++
 src/mess/machine/beta.c     | 10 +++++++---
 src/mess/machine/beta.h     |  2 +-
 3 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/src/mess/drivers/scorpion.c b/src/mess/drivers/scorpion.c
index de840193ade..80385da7774 100644
--- a/src/mess/drivers/scorpion.c
+++ b/src/mess/drivers/scorpion.c
@@ -322,6 +322,8 @@ ROM_START(scorpio)
 	ROMX_LOAD("scorp2.rom",   0x018000, 0x4000, CRC(fd0d3ce1) SHA1(07783ee295274d8ff15d935bfd787c8ac1d54900), ROM_BIOS(7))
 	ROMX_LOAD("scorp3.rom",   0x01c000, 0x4000, CRC(1fe1d003) SHA1(33703e97cc93b7edfcc0334b64233cf81b7930db), ROM_BIOS(7))
 
+	ROM_FILL( 0x1fe47, 1, 0x3e)	// patch TR-DOS bug
+
 	ROM_REGION(0x01000, "keyboard", 0)
 	ROM_LOAD( "scrpkey.rom", 0x0000, 0x1000, CRC(e938a510) SHA1(2753993c97ff0fc6cff26ed792929abc1288dc6f))
 
diff --git a/src/mess/machine/beta.c b/src/mess/machine/beta.c
index add547aef97..ff7187ba3e3 100644
--- a/src/mess/machine/beta.c
+++ b/src/mess/machine/beta.c
@@ -1,5 +1,5 @@
 // license:BSD-3-Clause
-// copyright-holders:Curt Coder
+// copyright-holders:Curt Coder, MetalliC
 /*********************************************************************
 
     beta.h
@@ -11,8 +11,7 @@
 *********************************************************************/
 /*
 BUGS:
-- random commands can be sent to FDC, so better keep .trd images write protected for now
-goto TR-DOS, CAT -> files will be shown, CAT again -> NO DISK mesage as result of trash commands
+- due to original firmware bug random commands can be sent to FDC instead of SEEK, current WD FDC emulation cant handle this correctly, use patch fix for now
 
 */
 #include "emu.h"
@@ -269,6 +268,11 @@ ROM_START( beta_disk )
 
 	//Default for now
 	ROM_LOAD( "trd503.rom",     0x00000, 0x4000, CRC(10751aba) SHA1(21695e3f2a8f796386ce66eea8a246b0ac44810c))
+
+	// TR-DOS rom have a bug - semi-random commands sent to FDC instead of SEEK command sometimes
+	// however it works OK on real hardware but does not using our WD FDC emulation, both legacy and modern
+	// this patch fixes original bug
+	ROM_FILL( 0x3e47, 1, 0x3e)
 ROM_END
 
 
diff --git a/src/mess/machine/beta.h b/src/mess/machine/beta.h
index e1a69d9a337..c082819149e 100644
--- a/src/mess/machine/beta.h
+++ b/src/mess/machine/beta.h
@@ -1,5 +1,5 @@
 // license:BSD-3-Clause
-// copyright-holders:Miodrag Milanovic
+// copyright-holders:Miodrag Milanovic, MetalliC
 /*********************************************************************
 
     beta.h