diff --git a/reactos/hal/halx86/generic/systimer.S b/reactos/hal/halx86/generic/systimer.S
index 0c0eaff656b..e2cfab608be 100644
--- a/reactos/hal/halx86/generic/systimer.S
+++ b/reactos/hal/halx86/generic/systimer.S
@@ -100,9 +100,9 @@ LoopPostInt:
 
     /* Check if someone updated the counter */
     cmp eax, ebx
-    jne LoopPostInt
+    jnz LoopPostInt
     cmp edx, esi
-    jne LoopPostInt
+    jnz LoopPostInt
 
     /* Check if the current 8254 value causes rollover */
     neg ecx
@@ -180,21 +180,35 @@ BelowHigh:
     or ecx, esi
     jz BelowLow
 
+    /* Make sure that the count is still valid */
+    sub ebx, eax
+    sbb esi, edx
+    jnz InvalidCount
+    cmp ebx, _HalpCurrentRollOver
+    jg InvalidCount
+
     /* Fixup the count with the last known value */
     sub eax, ebx
     sbb edx, esi
 
     /* We might have an incoming interrupt, save EFLAGS */
-    mov esi, [esp]
+    mov ecx, [esp]
     popf
 
     /* Check if interrupts were enabled and try again */
-    test esi, EFLAGS_INTERRUPT_MASK
+    test ecx, EFLAGS_INTERRUPT_MASK
     jnz LoopPreInt
 
     /* They're not, continue where we left */
     pushf
     jmp BelowLow
+
+InvalidCount:
+    popf
+    xor eax, eax
+    mov _HalpLastPerfCounterLow, eax
+    mov _HalpLastPerfCounterHigh, eax
+    jmp LoopPreInt
 .endfunc
 
 .globl _HalpClockInterrupt@0
diff --git a/reactos/hal/halx86/generic/timer.c b/reactos/hal/halx86/generic/timer.c
index df96244c0b6..0149b8a3394 100644
--- a/reactos/hal/halx86/generic/timer.c
+++ b/reactos/hal/halx86/generic/timer.c
@@ -48,6 +48,7 @@ HalpInitializeClock(VOID)
     PKPRCB Prcb = KeGetCurrentPrcb();
     ULONG Increment;
     USHORT RollOver;
+    ULONG Flags = 0;
 
     /* Check the CPU Type */
     if (Prcb->CpuType <= 4)
@@ -66,6 +67,7 @@ HalpInitializeClock(VOID)
     KeSetTimeIncrement(Increment, HalpRolloverTable[0].HighPart);
 
     /* Disable interrupts */
+    Ke386SaveFlags(Flags);
     _disable();
 
     /* Set the rollover */
@@ -73,8 +75,8 @@ HalpInitializeClock(VOID)
     __outbyte(TIMER_DATA_PORT0, RollOver & 0xFF);
     __outbyte(TIMER_DATA_PORT0, RollOver >> 8);
 
-    /* Restore interrupts */
-    _enable();
+    /* Restore interrupts if they were previously enabled */
+    Ke386RestoreFlags(Flags);
 
     /* Save rollover and return */
     HalpCurrentRollOver = RollOver;
@@ -90,18 +92,20 @@ NTAPI
 HalCalibratePerformanceCounter(IN volatile PLONG Count,
                                IN ULONGLONG NewCount)
 {
+    ULONG Flags = 0;
+
     /* Disable interrupts */
+    Ke386SaveFlags(Flags);
     _disable();
 
     /* Do a decrement for this CPU */
-    //_InterlockedDecrement(Count);
-    InterlockedDecrement(Count);
+    _InterlockedDecrement(Count);
 
     /* Wait for other CPUs */
     while (*Count);
 
-    /* Bring interrupts back */
-    _enable();
+    /* Restore interrupts if they were previously enabled */
+    Ke386RestoreFlags(Flags);
 }
 
 /*
diff --git a/reactos/include/ndk/asm.h b/reactos/include/ndk/asm.h
index 42a1072c47f..0888ba0f678 100644
--- a/reactos/include/ndk/asm.h
+++ b/reactos/include/ndk/asm.h
@@ -202,6 +202,7 @@ Author:
 #define KPCR_PRCB_DEBUG_DPC_TIME                0x654
 #define KPCR_PRCB_INTERRUPT_TIME                0x658
 #define KPCR_PRCB_ADJUST_DPC_THRESHOLD          0x65C
+#define KPCR_PRCB_SKIP_TICK                     0x664
 #define KPCR_SYSTEM_CALLS                       0x6B8
 #define KPCR_PRCB_DPC_QUEUE_DEPTH               0xA4C
 #define KPCR_PRCB_DPC_COUNT                     0xA50
diff --git a/reactos/lib/rtl/debug.c b/reactos/lib/rtl/debug.c
index 77f35e16904..308484551c7 100644
--- a/reactos/lib/rtl/debug.c
+++ b/reactos/lib/rtl/debug.c
@@ -142,7 +142,7 @@ vDbgPrintExWithPrefixInternal(IN LPCSTR Prefix,
         if (Status == STATUS_BREAKPOINT)
         {
             /* Breakpoint */
-            DbgBreakPointWithStatus(DBG_STATUS_CONTROL_C);
+            //DbgBreakPointWithStatus(DBG_STATUS_CONTROL_C);
             Status = STATUS_SUCCESS;
         }
     }
diff --git a/reactos/ntoskrnl/ke/i386/kiinit.c b/reactos/ntoskrnl/ke/i386/kiinit.c
index 11a60e5ba93..97c4da1044e 100644
--- a/reactos/ntoskrnl/ke/i386/kiinit.c
+++ b/reactos/ntoskrnl/ke/i386/kiinit.c
@@ -237,7 +237,7 @@ KiInitMachineDependent(VOID)
             if (KeFeatureBits & KF_MTRR)
             {
                 /* Then manually initialize MTRR for the CPU */
-                KiInitializeMTRR((BOOLEAN)i ? FALSE : TRUE);
+                KiInitializeMTRR(i ? FALSE : TRUE);
             }
 
             /* Check if we have AMD MTRR and initialize it for the CPU */
diff --git a/reactos/ntoskrnl/ke/i386/systimer.S b/reactos/ntoskrnl/ke/i386/systimer.S
index a2c54e93117..3a9883dd384 100644
--- a/reactos/ntoskrnl/ke/i386/systimer.S
+++ b/reactos/ntoskrnl/ke/i386/systimer.S
@@ -59,6 +59,10 @@ _KeUpdateRunTime@4:
     /* Get KPCR */
     mov eax, [fs:KPCR_SELF]
 
+    /* Check if this tick is getting skipped */
+    cmp byte ptr [eax+KPCR_PRCB_SKIP_TICK], 0
+    jnz SkipTick
+
     /* Save EBX */
     push ebx
 
@@ -84,11 +88,12 @@ _KeUpdateRunTime@4:
     ja AboveDispatch
 
     /* Check if the DPC routine is active */
-    cmp dword ptr[eax+KPCR_PRCB_DPC_ROUTINE_ACTIVE], 0
+    cmp byte ptr fs:[KPCR_PRCB_DPC_ROUTINE_ACTIVE], 0
     jz BelowDispatch
 
     /* At dispatch, increase DPC time */
     inc dword ptr [eax+KPCR_PRCB_DPC_TIME]
+    inc dword ptr [eax+KPCR_PRCB_DEBUG_DPC_TIME]
     jmp AfterSet
 
 AboveDispatch:
@@ -185,12 +190,21 @@ QuantumNotEmpty:
     /* Restore ebx and return */
     pop ebx
     ret 4
+
+SkipTick:
+    /* Disable skipping the next tick and return */
+    mov byte ptr [eax+KPCR_PRCB_SKIP_TICK], 0
+    ret 4
 .endfunc
 
 .globl _KeUpdateSystemTime@0
 .func KeUpdateSystemTime@0
 _KeUpdateSystemTime@0:
 
+    /* Check if this tick is getting skipped */
+    cmp byte ptr fs:[KPCR_PRCB_SKIP_TICK], 0
+    jnz SkipTickSys
+
     /* Get shared data in ECX */
     mov ecx, USER_SHARED_DATA
 
@@ -296,9 +310,12 @@ TimerExpired:
     call @HalRequestSoftwareInterrupt@4
 
 DebugCheck:
-    /* FIXME: Check for KdDebuggerEnabled */
+    /* Check if the debugger is enabled */
+    cmp dword ptr __KdDebuggerEnabled, 0
+    jnz DebuggerEnabled
 
     /* Check if this was a full tick */
+NoDebug:
     cmp dword ptr _KiTickOffset, 0
     jg IncompleteTick2
 
@@ -320,4 +337,20 @@ Done:
     cli
     call _HalEndSystemInterrupt@8
     jmp _Kei386EoiHelper@0
+
+DebuggerEnabled:
+    /* Check for break-in request */
+    call _KdPollBreakIn@0
+    or al, al
+    jz NoDebug
+
+    /* Break-in requested! */
+    push 1
+    call _DbgBreakPointWithStatus@4
+    jmp NoDebug
+
+SkipTickSys:
+    /* Disable skipping the next tick and return */
+    mov byte ptr fs:[KPCR_PRCB_SKIP_TICK], 0
+    jmp IncompleteTick2
 .endfunc