From 5c0b03c10c59ebcd522bb1e8afdd2674101b6772 Mon Sep 17 00:00:00 2001
From: ripsaw8080 <ripsaw8080@users.sourceforge.net>
Date: Sun, 10 Sep 2017 11:25:45 +0000
Subject: [PATCH] Process repeated reset commands without delay. Fixes MPU
 detection in several games. Correct ACK for reset: entirely absent with dumb
 setting (mpu401=uart), and also absent when returning to intelligent mode
 from UART mode.

Imported-from: https://svn.code.sf.net/p/dosbox/code-0/dosbox/trunk@4047
---
 src/hardware/mpu401.cpp | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/src/hardware/mpu401.cpp b/src/hardware/mpu401.cpp
index 1eff7ec3..a5aec2a6 100644
--- a/src/hardware/mpu401.cpp
+++ b/src/hardware/mpu401.cpp
@@ -122,7 +122,15 @@ static Bitu MPU401_ReadStatus(Bitu port,Bitu iolen) {
 }
 
 static void MPU401_WriteCommand(Bitu port,Bitu val,Bitu iolen) {
-	if (mpu.state.reset) {mpu.state.cmd_pending=val+1;return;}
+	if (mpu.mode==M_UART && val!=0xff) return;
+	if (mpu.state.reset) {
+		if (mpu.state.cmd_pending || (val!=0x3f && val!=0xff)) {
+			mpu.state.cmd_pending=val+1;
+			return;
+		}
+		PIC_RemoveEvents(MPU401_ResetDone);
+		mpu.state.reset=false;
+	}
 	if (val<=0x2f) {
 		switch (val&3) { /* MIDI stop, start, continue */
 			case 1: {MIDI_RawOutByte(0xfc);break;}
@@ -246,8 +254,11 @@ static void MPU401_WriteCommand(Bitu port,Bitu val,Bitu iolen) {
 			LOG(LOG_MISC,LOG_NORMAL)("MPU-401:Reset %X",val);
 			PIC_AddEvent(MPU401_ResetDone,MPU401_RESETBUSY);
 			mpu.state.reset=true;
+			if (mpu.mode==M_UART) {
+				MPU401_Reset();
+				return;	//do not send ack in UART mode
+			}
 			MPU401_Reset();
-			if (mpu.mode==M_UART) return;//do not send ack in UART mode
 			break;
 		case 0x3f:	/* UART mode */
 			LOG(LOG_MISC,LOG_NORMAL)("MPU-401:Set UART mode %X",val);
@@ -537,7 +548,6 @@ static void MPU401_Event(Bitu val) {
 	}
 	if (!mpu.state.irq_pending && mpu.state.req_mask) MPU401_EOIHandler();
 next_event:
-	PIC_RemoveEvents(MPU401_Event);
 	Bitu new_time;
 	if ((new_time=mpu.clock.tempo*mpu.clock.timebase)==0) return;
 	PIC_AddEvent(MPU401_Event,MPU401_TIMECONSTANT/new_time);