diff --git a/include/functions.h b/include/functions.h
index 94db5cfc72a..2e21e1be04e 100644
--- a/include/functions.h
+++ b/include/functions.h
@@ -102,7 +102,6 @@ extern "C" {
     void func_8036221C(void);
     void countUsed__FP10JKRExpHeap(void);
     void JUTReport(void);
-    void OSGetTime(void);
     void func_803621D0(void);
     void offEventBit__11dSv_event_cFUs(void);
     void func_803621C0(void);
diff --git a/include/os/OS.h b/include/os/OS.h
index 65e3bc2b3bb..02d0cb7ead2 100644
--- a/include/os/OS.h
+++ b/include/os/OS.h
@@ -1,60 +1,148 @@
-#ifndef __OS_H_
-#define __OS_H_
+// at some point: we should split this up into various OS/... headers. but not yet, since barely any files include this atm.
 
-struct OSThread {
-    u8 unkn[0x318];
-};
+#ifndef __OS_H__
+#define __OS_H__
 
-struct OSMessageQueue {
-    u8 unkn[0x20];
-};
+
+/* TODO: more structs, and get rid of the ones that are faked! */
 
 struct OSMutex {
-    u8 unkn[24];
+    u8 unk[24];
+};
+
+struct OSMutexLink {
+    struct OSMutex *prev;
+    struct OSMutex *next;
+};
+
+struct OSMutexQueue {
+    struct OSMutex *prev;
+    struct OSMutex *next;
+};
+
+struct OSThread {
+    u8 unk[792];
+};
+
+typedef void (*OSSwitchThreadCallback)(OSThread *from, OSThread *to);
+
+struct OSThreadLink {
+    struct OSThread * prev;
+    struct OSThread * next;
+};
+
+struct OSThreadQueue {
+    struct OSThread * head;
+    struct OSThread * tail;
+};
+
+struct OSCond {
+    struct OSThreadQueue queue;
 };
 
 typedef void* OSMessage;
+
+struct OSMessageQueue {
+    struct OSThreadQueue sending_queue;
+    struct OSThreadQueue receiving_queue;
+    void **message_array;
+    s32 num_messages;
+    s32 first_index;
+    s32 num_used;
+};
+
+typedef u32 OSTick;
+
+typedef s64 OSTime;
+
+struct OSCalendarTime {
+    s32 seconds;
+    s32 minutes;
+    s32 hours;
+    s32 day_of_month;
+    s32 month;
+    s32 year;
+    s32 week_day;
+    s32 year_day;
+    s32 milliseconds;
+    s32 microseconds;
+};
+
+typedef s32 OSHeapHandle;
+
+typedef enum OSSoundMode {
+    SOUND_MODE_MONO=0,
+    SOUND_MODE_STEREO=1,
+
+    __SOUND_MODE_FORCE_ENUM_U32=0xffffffff,
+} OSSoundMode;
+
 extern "C" {
-    void OSInitMutex(OSMutex*);
-    void OSLockMutex(OSMutex*);
-    void OSUnlockMutex(OSMutex*);
-    void OSEnableScheduler(void);
-    void OSDisableScheduler(void);
-    void OSCheckActiveThreads(void);
-    void OSReport_Error(char*,...);
-    u32 OSGetSoundMode(void);
-    void OSSuspendThread(void);
-    void OSSetThreadPriority(void);
-    void OSResumeThread(void);
-    void OSGetThreadPriority(void);
-    void OSGetConsoleType(void);
-    void OSGetResetCode(void);
-    void OSAllocFromArenaLo(void);
-    void OSReportInit(void);
+    s32 OSEnableScheduler(void);
+    s32 OSDisableScheduler(void);
+    s32 OSCheckActiveThreads(void);
     OSThread* OSGetCurrentThread(void);
-    void OSTicksToCalendarTime(void);
+
+    s32 OSSuspendThread(OSThread* thread);
+    s32 OSSetThreadPriority(OSThread* thread, u32 pri);
+    s32 OSGetThreadPriority(OSThread* thread);
+    s32 OSCreateThread(OSThread* thread, void* (*func)(void*), void* param,
+                    void* stack, u32 stackSize, int param_6, int param_7);
+    void OSCancelThread(OSThread* thread);
+    void OSDetachThread(OSThread* thread);
+    s32 OSResumeThread(OSThread *thread);
+    void OSExitThread(void *exit_val);
+    bool OSIsThreadSuspended(OSThread* thread);
+    bool OSIsThreadTerminated(OSThread* thread);
+    OSSwitchThreadCallback OSSetSwitchThreadCallback(OSSwitchThreadCallback *callback);
+
+    void OSInitMessageQueue(OSMessageQueue *queue, OSMessage* messages, int message_count);
+    void OSReceiveMessage(OSMessageQueue *queue, OSMessage message, int flags);
+    void OSSendMessage(OSMessageQueue *queue, OSMessage message, int flags);
+
+    s32 OSGetConsoleType(void);
+    s32 OSGetResetCode(void);
+
+    OSSoundMode OSGetSoundMode(void);
+    void OSSetSoundMode(OSSoundMode mode);
+
+    void OSReportInit(void);
+    void OSAttention(char *msg);
+    void OSPanic(char *file, s32 line, char* fmt, ...);
+    void OSReport(char *fmt, ...);
+    void OSReport_Error(char* fmt, ...);
+    void OSReport_FatalError(char* fmt, ...);
+    void OSReport_System(char* fmt, ...);
+    void OSReport_Warning(char* fmt, ...);
+    void OSReportDisable(void);
+    void OSReportEnable(void);
+    void OSReportForceEnableOff(void);
+    void OSReportForceEnableOn(void);
+    void OSReportInit(void);
+    void OSSwitchFiberEx(u32, u32, u32, u32, u32, u32);
+    void OSVAttention(char *, /*__gnuc_va_list*/ void*);
+
+    void OSTicksToCalendarTime(OSTime ticks, OSCalendarTime *out_time);
+    OSTime OSGetTime(void);
+    OSTick OSGetTick(void);
 
     u32 OSGetArenaLo();
     u32 OSGetArenaHi();
     u32 OSInitAlloc(u32 low, u32 high, int param_3);
     void OSSetArenaLo(u32 param_1);
     void OSSetArenaHi(u32 param_1);
+    void OSAllocFromArenaLo(u32 size, int alignment);
 
-    void OSGetTick(void);
-    void OSRestoreInterrupts(void);
-    void OSReport(void);
+    // void OSCancelAlarm(OSAlarm *alarm);
 
-    void OSCreateThread(OSThread* thread, void* (*func)(void*), void* param,
-                    void* stack, u32 stackSize, int param_6, int param_7);
-    void OSCancelThread(OSThread* thread);
-    void OSDetachThread(OSThread* thread);
-    bool OSIsThreadSuspended(OSThread* thread);
-    bool OSIsThreadTerminated(OSThread* thread);
-    void OSInitMessageQueue(OSMessageQueue *queue, OSMessage* messages, int message_count);
-    void OSSetSwitchThreadCallback(void);
-    void OSReceiveMessage(OSMessageQueue *queue, OSMessage message, int flags);
-    void OSSendMessage(OSMessageQueue *queue, OSMessage message, int flags);
-}
+    void OSInitMutex(OSMutex *mutex);
+    void OSLockMutex(OSMutex *mutex);
+    void OSTryLockMutex(OSMutex *mutex);
+    void OSUnlockMutex(OSMutex *mutex);
 
+    s32 OSDisableInterrupts();
+    s32 OSEnableInterrupts();
+    s32 OSRestoreInterrupts(s32 level);
+};
 
 #endif
\ No newline at end of file
diff --git a/src/d/d_save/d_save.cpp b/src/d/d_save/d_save.cpp
index aa5e0b5dea7..6c0f028bb01 100644
--- a/src/d/d_save/d_save.cpp
+++ b/src/d/d_save/d_save.cpp
@@ -1,6 +1,7 @@
 #include "d/d_save/d_save/d_save.h"
 
 #include "d/d_com/d_com_inf_game/d_com_inf_game.h"
+#include "os/OS.h"
 
 u8 dSv_item_rename(u8 item_id) {
     switch (item_id) {
@@ -854,11 +855,11 @@ asm void dSv_player_info_c::init(void) {
 #endif
 
 void dSv_player_config_c::init(void) {
-    u32 os_sound_mode;
+    OSSoundMode os_sound_mode;
 
     this->unk0 = 1;
     os_sound_mode = OSGetSoundMode();
-    if (os_sound_mode == 0) {
+    if (os_sound_mode == SOUND_MODE_MONO) {
         this->sound_mode = 0;
         Z2AudioMgr_NS_setOutputMode(lbl_80451368, 0);
     } else {