From cc89902e00088970b069e5001a1773322799a793 Mon Sep 17 00:00:00 2001
From: Aleksandar Andrejevic <aandrejevic@reactos.org>
Date: Sun, 10 Nov 2013 00:53:05 +0000
Subject: [PATCH] [NTVDM] Don't enable interrupts unless it's necessary in the
 interrupt handler. [FAST486] When handling interrupt signals, make sure at
 least one instruction is executed, to prevent the CPU from being completely
 blocked by interrupt signals.

svn path=/branches/ntvdm/; revision=60910
---
 lib/fast486/fast486.c    | 21 +++++++++++----------
 subsystems/ntvdm/int32.c |  6 ++++--
 2 files changed, 15 insertions(+), 12 deletions(-)

diff --git a/lib/fast486/fast486.c b/lib/fast486/fast486.c
index dcb98b30157..05ee5596432 100644
--- a/lib/fast486/fast486.c
+++ b/lib/fast486/fast486.c
@@ -63,19 +63,10 @@ Fast486ExecutionControl(PFAST486_STATE State, INT Command)
              * Check if there is an interrupt to execute, or a hardware interrupt signal
              * while interrupts are enabled.
              */
-            if ((State->IntStatus == FAST486_INT_EXECUTE)
-                || (State->Flags.If
-                && (State->IntAckCallback != NULL)
-                && (State->IntStatus == FAST486_INT_SIGNAL)))
+            if (State->IntStatus == FAST486_INT_EXECUTE)
             {
                 FAST486_IDT_ENTRY IdtEntry;
 
-                if (State->IntStatus == FAST486_INT_SIGNAL)
-                {
-                    /* Acknowledge the interrupt to get the number */
-                    State->PendingIntNum = State->IntAckCallback(State);
-                }
-
                 /* Get the interrupt vector */
                 if (Fast486GetIntVector(State, State->PendingIntNum, &IdtEntry))
                 {
@@ -89,6 +80,16 @@ Fast486ExecutionControl(PFAST486_STATE State, INT Command)
                 /* Clear the interrupt status */
                 State->IntStatus = FAST486_INT_NONE;
             }
+            else if (State->Flags.If
+                     && (State->IntAckCallback != NULL)
+                     && (State->IntStatus == FAST486_INT_SIGNAL))
+            {
+                /* Acknowledge the interrupt to get the number */
+                State->PendingIntNum = State->IntAckCallback(State);
+
+                /* Set the interrupt status to execute on the next instruction */
+                State->IntStatus = FAST486_INT_EXECUTE;
+            }
         }
 
         /* Perform an instruction fetch */
diff --git a/subsystems/ntvdm/int32.c b/subsystems/ntvdm/int32.c
index 8e039333587..8d4455511ec 100644
--- a/subsystems/ntvdm/int32.c
+++ b/subsystems/ntvdm/int32.c
@@ -139,7 +139,7 @@ VOID WINAPI InitializeInt32(WORD BiosSegment)
     {
         IntVecTable[i] = MAKELONG(Offset, BiosSegment);
 
-        BiosCode[Offset++] = 0xFB; // sti
+        BiosCode[Offset++] = 0xFA; // cli
 
         BiosCode[Offset++] = 0x6A; // push i
         BiosCode[Offset++] = (UCHAR)i;
@@ -158,11 +158,13 @@ VOID WINAPI InitializeInt32(WORD BiosSegment)
         BiosCode[Offset++] = 0x73; // jnc EXIT (offset +3)
         BiosCode[Offset++] = 0x03;
 
+        BiosCode[Offset++] = 0xFB; // sti
+
         // HACK: The following instruction should be HLT!
         BiosCode[Offset++] = 0x90; // nop
 
         BiosCode[Offset++] = 0xEB; // jmp BOP_SEQ (offset -10)
-        BiosCode[Offset++] = 0xF6;
+        BiosCode[Offset++] = 0xF5;
 
 // EXIT:
         BiosCode[Offset++] = 0x83; // add sp, 4