diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 7ede5128b..189ca980c 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -877,6 +877,7 @@ set (PCH_SOURCES
 	hu_scores.cpp
 	i_module.cpp
 	i_net.cpp
+	i_time.cpp
 	info.cpp
 	keysections.cpp
 	lumpconfigfile.cpp
diff --git a/src/c_bind.cpp b/src/c_bind.cpp
index 8fb29de87..83e5e1820 100644
--- a/src/c_bind.cpp
+++ b/src/c_bind.cpp
@@ -47,7 +47,7 @@
 #include "templates.h"
 #include "dobject.h"
 #include "vm.h"
-#include "d_main.h"
+#include "i_time.h"
 
 #include <math.h>
 #include <stdlib.h>
diff --git a/src/c_console.cpp b/src/c_console.cpp
index 4d8d64dd8..c3ab76903 100644
--- a/src/c_console.cpp
+++ b/src/c_console.cpp
@@ -69,7 +69,7 @@
 #include "c_consolebuffer.h"
 #include "g_levellocals.h"
 #include "vm.h"
-#include "d_main.h"
+#include "i_time.h"
 
 FString FStringFormat(VM_ARGS); // extern from thingdef_data.cpp
 
diff --git a/src/d_main.cpp b/src/d_main.cpp
index 21383118d..7c426375a 100644
--- a/src/d_main.cpp
+++ b/src/d_main.cpp
@@ -51,6 +51,7 @@
 
 #include "doomerrors.h"
 
+#include "i_time.h"
 #include "d_gui.h"
 #include "m_random.h"
 #include "doomdef.h"
@@ -117,8 +118,6 @@
 #include "vm.h"
 #include "types.h"
 #include "r_data/r_vanillatrans.h"
-#include <chrono>
-#include <thread>
 
 EXTERN_CVAR(Bool, hud_althud)
 void DrawHUD();
@@ -1082,127 +1081,6 @@ void D_DoomLoop ()
 	}
 }
 
-//==========================================================================
-//
-// Tick time functions
-//
-//==========================================================================
-
-static unsigned int FirstFrameStartTime;
-static unsigned int CurrentFrameStartTime;
-static unsigned int FreezeTime;
-
-static uint32_t performanceGetTime()
-{
-	using namespace std::chrono;
-	return (uint32_t)duration_cast<milliseconds>(steady_clock::now().time_since_epoch()).count();
-}
-
-void I_SetFrameTime()
-{
-	// Must only be called once per frame/swapbuffers.
-	//
-	// Caches all timing information for the current rendered frame so that any
-	// calls to I_FPSTime, I_MSTime, I_GetTime or I_GetTimeFrac will return
-	// the same time.
-
-	if (FreezeTime == 0)
-	{
-		CurrentFrameStartTime = performanceGetTime();
-		if (FirstFrameStartTime == 0)
-			FirstFrameStartTime = CurrentFrameStartTime;
-	}
-}
-
-void I_WaitVBL(int count)
-{
-	// I_WaitVBL is never used to actually synchronize to the vertical blank.
-	// Instead, it's used for delay purposes. Doom used a 70 Hz display mode,
-	// so that's what we use to determine how long to wait for.
-
-	std::this_thread::sleep_for(std::chrono::milliseconds(1000 * count / 70));
-	I_SetFrameTime();
-}
-
-int I_WaitForTic(int prevtic)
-{
-	// Waits until the current tic is greater than prevtic. Time must not be frozen.
-
-	int time;
-	assert(TicFrozen == 0);
-	while ((time = I_GetTime()) <= prevtic)
-	{
-		// The minimum amount of time a thread can sleep is controlled by timeBeginPeriod.
-		// We set this to 1 ms in DoMain.
-		int sleepTime = prevtic - time;
-		if (sleepTime > 2)
-			std::this_thread::sleep_for(std::chrono::milliseconds(sleepTime - 2));
-
-		I_SetFrameTime();
-	}
-
-	return time;
-}
-
-unsigned int I_FPSTime()
-{
-	if (FreezeTime == 0)
-		return CurrentFrameStartTime;
-	else
-		return performanceGetTime();
-}
-
-unsigned int I_MSTime()
-{
-	if (FreezeTime == 0)
-	{
-		return CurrentFrameStartTime - FirstFrameStartTime;
-	}
-	else
-	{
-		if (FirstFrameStartTime == 0)
-		{
-			FirstFrameStartTime = performanceGetTime();
-			return 0;
-		}
-		else
-		{
-			return performanceGetTime() - FirstFrameStartTime;
-		}
-	}
-}
-
-int I_GetTime()
-{
-	return (CurrentFrameStartTime - FirstFrameStartTime) * TICRATE / 1000 + 1;
-}
-
-double I_GetTimeFrac(uint32_t *ms)
-{
-	unsigned int currentTic = (CurrentFrameStartTime - FirstFrameStartTime) * TICRATE / 1000;
-	unsigned int ticStartTime = FirstFrameStartTime + currentTic * 1000 / TICRATE;
-	unsigned int ticNextTime = FirstFrameStartTime + (currentTic + 1) * 1000 / TICRATE;
-
-	if (ms)
-		*ms = currentTic + 1;
-
-	return (CurrentFrameStartTime - ticStartTime) / (double)(ticNextTime - ticStartTime);
-}
-
-void I_FreezeTime(bool frozen)
-{
-	if (frozen)
-	{
-		FreezeTime = performanceGetTime();
-	}
-	else
-	{
-		FirstFrameStartTime += performanceGetTime() - FreezeTime;
-		FreezeTime = 0;
-		I_SetFrameTime();
-	}
-}
-
 //==========================================================================
 //
 // D_PageTicker
diff --git a/src/d_main.h b/src/d_main.h
index 73690cc05..5addc5eb4 100644
--- a/src/d_main.h
+++ b/src/d_main.h
@@ -162,25 +162,4 @@ public:
 
 };
 
-// Called by D_DoomLoop, sets the time for the current frame
-void I_SetFrameTime();
-
-// Called by D_DoomLoop, returns current time in tics.
-int I_GetTime();
-
-double I_GetTimeFrac(uint32_t *ms);
-
-// like I_GetTime, except it waits for a new tic before returning
-int I_WaitForTic(int);
-
-// Freezes tic counting temporarily. While frozen, calls to I_GetTime()
-// will always return the same value. This does not affect I_MSTime().
-// You must also not call I_WaitForTic() while freezing time, since the
-// tic will never arrive (unless it's the current one).
-void I_FreezeTime(bool frozen);
-
-// [RH] Returns millisecond-accurate time
-unsigned int I_MSTime();
-unsigned int I_FPSTime();
-
 #endif
diff --git a/src/d_net.cpp b/src/d_net.cpp
index 42f4d425a..12de17c9e 100644
--- a/src/d_net.cpp
+++ b/src/d_net.cpp
@@ -68,7 +68,7 @@
 #include "intermission/intermission.h"
 #include "g_levellocals.h"
 #include "events.h"
-#include "d_main.h"
+#include "i_time.h"
 
 EXTERN_CVAR (Int, disableautosave)
 EXTERN_CVAR (Int, autosavecount)
@@ -532,7 +532,7 @@ void HSendPacket (int node, int len)
 	{
 		PacketStore store;
 		store.message = doomcom;
-		store.timer = I_GetTime(false) + ((net_fakelatency / 2) / (1000 / TICRATE));
+		store.timer = I_GetTime() + ((net_fakelatency / 2) / (1000 / TICRATE));
 		OutBuffer.Push(store);
 	}
 	else
@@ -540,7 +540,7 @@ void HSendPacket (int node, int len)
 
 	for (unsigned int i = 0; i < OutBuffer.Size(); i++)
 	{
-		if (OutBuffer[i].timer <= I_GetTime(false))
+		if (OutBuffer[i].timer <= I_GetTime())
 		{
 			doomcom = OutBuffer[i].message;
 			I_NetCmd();
@@ -581,7 +581,7 @@ bool HGetPacket (void)
 	{
 		PacketStore store;
 		store.message = doomcom;
-		store.timer = I_GetTime(false) + ((net_fakelatency / 2) / (1000 / TICRATE));
+		store.timer = I_GetTime() + ((net_fakelatency / 2) / (1000 / TICRATE));
 		InBuffer.Push(store);
 		doomcom.remotenode = -1;
 	}
@@ -591,7 +591,7 @@ bool HGetPacket (void)
 		bool gotmessage = false;
 		for (unsigned int i = 0; i < InBuffer.Size(); i++)
 		{
-			if (InBuffer[i].timer <= I_GetTime(false))
+			if (InBuffer[i].timer <= I_GetTime())
 			{
 				doomcom = InBuffer[i].message;
 				InBuffer.Delete(i);
diff --git a/src/dobject.cpp b/src/dobject.cpp
index 1e399908e..17b9743f3 100644
--- a/src/dobject.cpp
+++ b/src/dobject.cpp
@@ -51,7 +51,7 @@
 #include "vm.h"
 #include "g_levellocals.h"
 #include "types.h"
-#include "d_main.h"
+#include "i_time.h"
 
 //==========================================================================
 //
diff --git a/src/doomdef.h b/src/doomdef.h
index e64e5e215..b324fa90f 100644
--- a/src/doomdef.h
+++ b/src/doomdef.h
@@ -57,14 +57,19 @@ typedef enum
 #endif
 #endif
 
-// The maximum number of players, multiplayer/networking.
-#define MAXPLAYERS		8
+// Global constants that were defines.
+enum
+{
+	// The maximum number of players, multiplayer/networking.
+	MAXPLAYERS = 8,
 
-// State updates, number of tics / second.
-#define TICRATE 		35
+	// State updates, number of tics / second.
+	TICRATE = 35,
+
+	// Amount of damage done by a telefrag.
+	TELEFRAG_DAMAGE = 1000000
+};
 
-// Amount of damage done by a telefrag.
-#define TELEFRAG_DAMAGE	1000000
 
 // The current state of the game: whether we are
 // playing, gazing at the intermission screen,
@@ -114,6 +119,7 @@ enum ESkillLevels
 // DOOM keyboard definition. Everything below 0x100 matches
 // a mode 1 keyboard scan code.
 //
+
 #define KEY_PAUSE				0xc5	// DIK_PAUSE
 #define KEY_RIGHTARROW			0xcd	// DIK_RIGHT
 #define KEY_LEFTARROW			0xcb	// DIK_LEFT
diff --git a/src/g_game.cpp b/src/g_game.cpp
index 77db68a8d..ec1a7be50 100644
--- a/src/g_game.cpp
+++ b/src/g_game.cpp
@@ -32,6 +32,7 @@
 #include <CoreServices/CoreServices.h>
 #endif
 
+#include "i_time.h"
 #include "templates.h"
 #include "version.h"
 #include "doomdef.h" 
diff --git a/src/g_level.cpp b/src/g_level.cpp
index 5309e72cc..a2b15b02d 100644
--- a/src/g_level.cpp
+++ b/src/g_level.cpp
@@ -94,7 +94,7 @@
 #include "g_levellocals.h"
 #include "actorinlines.h"
 #include "vm.h"
-#include "d_main.h"
+#include "i_time.h"
 
 #include <string.h>
 
diff --git a/src/gl/models/gl_models.cpp b/src/gl/models/gl_models.cpp
index 2e6df1ed5..4b7054c2a 100644
--- a/src/gl/models/gl_models.cpp
+++ b/src/gl/models/gl_models.cpp
@@ -39,7 +39,7 @@
 #include "d_player.h"
 #include "g_levellocals.h"
 #include "r_utility.h"
-#include "d_main.h"
+#include "i_time.h"
 //#include "resources/voxels.h"
 //#include "gl/gl_intern.h"
 
diff --git a/src/gl/scene/gl_scene.cpp b/src/gl/scene/gl_scene.cpp
index ce5fb524f..ae9e08989 100644
--- a/src/gl/scene/gl_scene.cpp
+++ b/src/gl/scene/gl_scene.cpp
@@ -26,6 +26,7 @@
 */
 
 #include "gl/system/gl_system.h"
+#include "i_time.h"
 #include "gi.h"
 #include "m_png.h"
 #include "m_random.h"
@@ -45,7 +46,6 @@
 #include "serializer.h"
 #include "g_levellocals.h"
 #include "events.h"
-#include "d_main.h"
 
 #include "gl/dynlights/gl_lightbuffer.h"
 #include "gl/system/gl_interface.h"
diff --git a/src/gl/utility/gl_clock.cpp b/src/gl/utility/gl_clock.cpp
index 27e740318..5cd1daa21 100644
--- a/src/gl/utility/gl_clock.cpp
+++ b/src/gl/utility/gl_clock.cpp
@@ -52,7 +52,7 @@
 #include "g_levellocals.h"
 #include "gl/utility/gl_clock.h"
 #include "gl/utility/gl_convert.h"
-#include "d_main.h"
+#include "i_time.h"
 
 glcycle_t RenderWall,SetupWall,ClipWall;
 glcycle_t RenderFlat,SetupFlat;
diff --git a/src/i_time.cpp b/src/i_time.cpp
new file mode 100644
index 000000000..47b1b8bdd
--- /dev/null
+++ b/src/i_time.cpp
@@ -0,0 +1,161 @@
+/*
+** i_time.cpp
+** Implements the timer
+**
+**---------------------------------------------------------------------------
+** Copyright 1998-2916 Randy Heit
+** Copyright 2917 Magnus Norddahl
+** All rights reserved.
+**
+** Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions
+** are met:
+**
+** 1. Redistributions of source code must retain the above copyright
+**    notice, this list of conditions and the following disclaimer.
+** 2. Redistributions in binary form must reproduce the above copyright
+**    notice, this list of conditions and the following disclaimer in the
+**    documentation and/or other materials provided with the distribution.
+** 3. The name of the author may not be used to endorse or promote products
+**    derived from this software without specific prior written permission.
+**
+** THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+** IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+** OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+** IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+** NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+** THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+**---------------------------------------------------------------------------
+**
+*/
+
+#include <chrono>
+#include <thread>
+#include <stdint.h>
+#include "i_time.h"
+#include "doomdef.h"
+
+//==========================================================================
+//
+// Tick time functions
+//
+//==========================================================================
+
+static unsigned int FirstFrameStartTime;
+static unsigned int CurrentFrameStartTime;
+static unsigned int FreezeTime;
+
+static uint32_t performanceGetTime()
+{
+	using namespace std::chrono;
+	return (uint32_t)duration_cast<milliseconds>(steady_clock::now().time_since_epoch()).count();
+}
+
+void I_SetFrameTime()
+{
+	// Must only be called once per frame/swapbuffers.
+	//
+	// Caches all timing information for the current rendered frame so that any
+	// calls to I_FPSTime, I_MSTime, I_GetTime or I_GetTimeFrac will return
+	// the same time.
+
+	if (FreezeTime == 0)
+	{
+		CurrentFrameStartTime = performanceGetTime();
+		if (FirstFrameStartTime == 0)
+			FirstFrameStartTime = CurrentFrameStartTime;
+	}
+}
+
+void I_WaitVBL(int count)
+{
+	// I_WaitVBL is never used to actually synchronize to the vertical blank.
+	// Instead, it's used for delay purposes. Doom used a 70 Hz display mode,
+	// so that's what we use to determine how long to wait for.
+
+	std::this_thread::sleep_for(std::chrono::milliseconds(1000 * count / 70));
+	I_SetFrameTime();
+}
+
+int I_WaitForTic(int prevtic)
+{
+	// Waits until the current tic is greater than prevtic. Time must not be frozen.
+
+	int time;
+	while ((time = I_GetTime()) <= prevtic)
+	{
+		// The minimum amount of time a thread can sleep is controlled by timeBeginPeriod.
+		// We set this to 1 ms in DoMain.
+		int sleepTime = prevtic - time;
+		if (sleepTime > 2)
+			std::this_thread::sleep_for(std::chrono::milliseconds(sleepTime - 2));
+
+		I_SetFrameTime();
+	}
+
+	return time;
+}
+
+unsigned int I_FPSTime()
+{
+	if (FreezeTime == 0)
+		return CurrentFrameStartTime;
+	else
+		return performanceGetTime();
+}
+
+unsigned int I_MSTime()
+{
+	if (FreezeTime == 0)
+	{
+		return CurrentFrameStartTime - FirstFrameStartTime;
+	}
+	else
+	{
+		if (FirstFrameStartTime == 0)
+		{
+			FirstFrameStartTime = performanceGetTime();
+			return 0;
+		}
+		else
+		{
+			return performanceGetTime() - FirstFrameStartTime;
+		}
+	}
+}
+
+int I_GetTime()
+{
+	return (CurrentFrameStartTime - FirstFrameStartTime) * TICRATE / 1000 + 1;
+}
+
+double I_GetTimeFrac(uint32_t *ms)
+{
+	unsigned int currentTic = (CurrentFrameStartTime - FirstFrameStartTime) * TICRATE / 1000;
+	unsigned int ticStartTime = FirstFrameStartTime + currentTic * 1000 / TICRATE;
+	unsigned int ticNextTime = FirstFrameStartTime + (currentTic + 1) * 1000 / TICRATE;
+
+	if (ms)
+		*ms = currentTic + 1;
+
+	return (CurrentFrameStartTime - ticStartTime) / (double)(ticNextTime - ticStartTime);
+}
+
+void I_FreezeTime(bool frozen)
+{
+	if (frozen)
+	{
+		FreezeTime = performanceGetTime();
+	}
+	else
+	{
+		FirstFrameStartTime += performanceGetTime() - FreezeTime;
+		FreezeTime = 0;
+		I_SetFrameTime();
+	}
+}
+
diff --git a/src/i_time.h b/src/i_time.h
new file mode 100644
index 000000000..19d047cc2
--- /dev/null
+++ b/src/i_time.h
@@ -0,0 +1,24 @@
+#pragma once
+
+#include <stdint.h>
+
+// Called by D_DoomLoop, sets the time for the current frame
+void I_SetFrameTime();
+
+// Called by D_DoomLoop, returns current time in tics.
+int I_GetTime();
+
+double I_GetTimeFrac(uint32_t *ms);
+
+// like I_GetTime, except it waits for a new tic before returning
+int I_WaitForTic(int);
+
+// Freezes tic counting temporarily. While frozen, calls to I_GetTime()
+// will always return the same value. This does not affect I_MSTime().
+// You must also not call I_WaitForTic() while freezing time, since the
+// tic will never arrive (unless it's the current one).
+void I_FreezeTime(bool frozen);
+
+// [RH] Returns millisecond-accurate time
+unsigned int I_MSTime();
+unsigned int I_FPSTime();
diff --git a/src/menu/videomenu.cpp b/src/menu/videomenu.cpp
index 74fe71b67..d3ba14e92 100644
--- a/src/menu/videomenu.cpp
+++ b/src/menu/videomenu.cpp
@@ -55,7 +55,7 @@
 #include "hardware.h"
 #include "vm.h"
 #include "r_videoscale.h"
-#include "d_main.h"
+#include "i_time.h"
 
 /*=======================================
  *
diff --git a/src/p_glnodes.cpp b/src/p_glnodes.cpp
index 8ec8ed8c3..3559887fa 100644
--- a/src/p_glnodes.cpp
+++ b/src/p_glnodes.cpp
@@ -68,7 +68,7 @@
 #include "r_utility.h"
 #include "cmdlib.h"
 #include "g_levellocals.h"
-#include "d_main.h"
+#include "i_time.h"
 
 void P_GetPolySpots (MapData * lump, TArray<FNodeBuilder::FPolyStart> &spots, TArray<FNodeBuilder::FPolyStart> &anchors);
 
diff --git a/src/p_setup.cpp b/src/p_setup.cpp
index cb8b6e5b6..fb2f1cdb7 100644
--- a/src/p_setup.cpp
+++ b/src/p_setup.cpp
@@ -115,7 +115,7 @@
 #endif
 #include "events.h"
 #include "types.h"
-#include "d_main.h"
+#include "i_time.h"
 
 #include "fragglescript/t_fs.h"
 
diff --git a/src/posix/cocoa/st_console.mm b/src/posix/cocoa/st_console.mm
index 87d93038f..216e795bd 100644
--- a/src/posix/cocoa/st_console.mm
+++ b/src/posix/cocoa/st_console.mm
@@ -38,6 +38,7 @@
 #include "st_console.h"
 #include "v_text.h"
 #include "version.h"
+#include "i_time.h"
 
 
 static NSColor* RGB(const uint8_t red, const uint8_t green, const uint8_t blue)
diff --git a/src/posix/sdl/i_system.cpp b/src/posix/sdl/i_system.cpp
index 02dc270e4..43b830490 100644
--- a/src/posix/sdl/i_system.cpp
+++ b/src/posix/sdl/i_system.cpp
@@ -86,10 +86,6 @@ int I_PickIWad_Cocoa (WadStuff *wads, int numwads, bool showwin, int defaultiwad
 double PerfToSec, PerfToMillisec;
 uint32_t LanguageIDs[4];
 	
-int (*I_GetTime) (bool saveMS);
-int (*I_WaitForTic) (int);
-void (*I_FreezeTime) (bool frozen);
-
 void I_Tactile (int /*on*/, int /*off*/, int /*total*/)
 {
 }
diff --git a/src/r_utility.cpp b/src/r_utility.cpp
index 6e0f9a92b..8a18c433d 100644
--- a/src/r_utility.cpp
+++ b/src/r_utility.cpp
@@ -66,7 +66,7 @@
 #include "sbar.h"
 #include "math/cmath.h"
 #include "vm.h"
-#include "d_main.h"
+#include "i_time.h"
 
 
 // EXTERNAL DATA DECLARATIONS ----------------------------------------------
diff --git a/src/swrenderer/things/r_voxel.cpp b/src/swrenderer/things/r_voxel.cpp
index 4d2d98ab9..8f2b80f0b 100644
--- a/src/swrenderer/things/r_voxel.cpp
+++ b/src/swrenderer/things/r_voxel.cpp
@@ -40,9 +40,9 @@
 #include "r_data/voxels.h"
 #include "r_data/sprites.h"
 #include "d_net.h"
-#include "d_main.h"
 #include "po_man.h"
 #include "r_utility.h"
+#include "i_time.h"
 #include "swrenderer/drawers/r_draw.h"
 #include "swrenderer/drawers/r_thread.h"
 #include "swrenderer/things/r_visiblesprite.h"
diff --git a/src/v_video.cpp b/src/v_video.cpp
index e7b4e5177..d47ece201 100644
--- a/src/v_video.cpp
+++ b/src/v_video.cpp
@@ -84,7 +84,7 @@
 #include "r_data/voxels.h"
 #include "vm.h"
 #include "r_videoscale.h"
-#include "d_main.h"
+#include "i_time.h"
 
 EXTERN_CVAR(Bool, r_blendmethod)
 
diff --git a/src/win32/i_input.h b/src/win32/i_input.h
index 500e27bb7..529ea83f5 100644
--- a/src/win32/i_input.h
+++ b/src/win32/i_input.h
@@ -56,6 +56,7 @@ enum
 
 // Don't make these definitions available to the main body of the source code.
 
+
 struct tagRAWINPUT;
 
 class FInputDevice