From 8a0bf29dd894b1cb19c0b8d4278859ada2802b1a Mon Sep 17 00:00:00 2001
From: gm-matthew <108370479+gm-matthew@users.noreply.github.com>
Date: Mon, 20 May 2024 13:38:45 +0100
Subject: [PATCH] Sound IRQs are acknowledged by writing to MIDI data port

---
 Src/Model3/Model3.cpp | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/Src/Model3/Model3.cpp b/Src/Model3/Model3.cpp
index ecb3701..8d71692 100644
--- a/Src/Model3/Model3.cpp
+++ b/Src/Model3/Model3.cpp
@@ -1418,8 +1418,11 @@ void CModel3::Write8(UINT32 addr, UINT8 data)
     // Sound Board
     case 0x08:
       //printf("PPC: %08X=%02X * (PC=%08X, LR=%08X)\n", addr, data, ppc_get_pc(), ppc_get_lr());
-      if ((addr&0xF) == 0)      // MIDI data port
+      if ((addr & 0xF) == 0)      // MIDI data port
+      {
         SoundBoard.WriteMIDIPort(data);
+        IRQ.Deassert(0x40);
+      }
       else if ((addr&0xF) == 4) // MIDI control port
         midiCtrlPort = data;
       break;
@@ -2133,9 +2136,7 @@ void CModel3::RunMainBoardFrame(void)
 
 			// Process MIDI interrupt
 			IRQ.Assert(0x40);
-			ppc_execute(200); // give PowerPC time to acknowledge IR
-			IRQ.Deassert(0x40);
-			ppc_execute(200); // acknowledge that IRQ was deasserted (TODO: is this really needed?)
+			ppc_execute(400); // give PowerPC time to acknowledge IR
 			dispCycles -= 400;
 
 			++irqCount;