From 83bc3035e6d81220cc08d2f05a85e00c102de6ef Mon Sep 17 00:00:00 2001
From: AJR <ajrhacker@users.noreply.github.com>
Date: Mon, 21 Jan 2019 14:00:19 -0500
Subject: [PATCH] ins8250: Allow writes to MSR with lower 4 bits zero to clear
 the associated interrupt. This is not confirmed behavior, but is logically
 consistent with nonzero bits causing interrupts when written.

---
 src/devices/machine/ins8250.cpp | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/devices/machine/ins8250.cpp b/src/devices/machine/ins8250.cpp
index 88262cdbac2..d127ce0e40d 100644
--- a/src/devices/machine/ins8250.cpp
+++ b/src/devices/machine/ins8250.cpp
@@ -390,6 +390,8 @@ WRITE8_MEMBER( ins8250_uart_device::ins8250_w )
 
 			if ( m_regs.msr & 0x0f )
 				trigger_int(COM_INT_PENDING_MODEM_STATUS_REGISTER);
+			else
+				clear_int(COM_INT_PENDING_MODEM_STATUS_REGISTER);
 			break;
 		case 7:
 			m_regs.scr = data;