diff --git a/include/PR/os.h b/include/PR/os.h
index 1b39d79a17..8b55f5bcb7 100644
--- a/include/PR/os.h
+++ b/include/PR/os.h
@@ -24,4 +24,15 @@
 #include "os_vi.h"
 #include "os_voice.h"
 
+/*
+ * Stack size for I/O device managers: PIM (PI Manager), VIM (VI Manager),
+ *	SIM (SI Manager)
+ *
+ */
+#define OS_PIM_STACKSIZE	4096
+#define OS_VIM_STACKSIZE	4096
+#define OS_SIM_STACKSIZE	4096
+
+#define	OS_MIN_STACKSIZE	72
+
 #endif
diff --git a/include/PR/os_internal.h b/include/PR/os_internal.h
index 916e82d7c6..f2c5bfa177 100644
--- a/include/PR/os_internal.h
+++ b/include/PR/os_internal.h
@@ -4,6 +4,7 @@
 #include "ultratypes.h"
 #include "os_message.h"
 #include "os_pi.h"
+#include "os_internal_rsp.h"
 
 typedef struct __osHwInt {
     /* 0x00 */ s32 (*handler)(void);
diff --git a/include/PR/os_internal_rsp.h b/include/PR/os_internal_rsp.h
new file mode 100644
index 0000000000..58c734f935
--- /dev/null
+++ b/include/PR/os_internal_rsp.h
@@ -0,0 +1,14 @@
+#ifndef PR_RSP_H
+#define PR_RSP_H
+
+#include "ultratypes.h"
+#include "libc/stddef.h"
+
+
+u32 __osSpGetStatus(void);
+void __osSpSetStatus(u32 data);
+s32 __osSpSetPc(u32 pc);
+s32 __osSpRawStartDma(s32 direction, u32 devAddr, void* dramAddr, size_t size);
+
+
+#endif
diff --git a/include/PR/rcp.h b/include/PR/rcp.h
index 18a2379418..919e6e90a1 100644
--- a/include/PR/rcp.h
+++ b/include/PR/rcp.h
@@ -108,6 +108,73 @@
 #define SP_IMEM_START   0x04001000
 #define SP_IMEM_END     0x04001FFF
 
+/**
+ * SP_STATUS_REG: write bits
+ */
+#define SP_CLR_HALT        (1 <<  0)
+#define SP_SET_HALT        (1 <<  1)
+#define SP_CLR_BROKE       (1 <<  2)
+#define SP_CLR_INTR        (1 <<  3)
+#define SP_SET_INTR        (1 <<  4)
+#define SP_CLR_SSTEP       (1 <<  5)
+#define SP_SET_SSTEP       (1 <<  6)
+#define SP_CLR_INTR_BREAK  (1 <<  7)
+#define SP_SET_INTR_BREAK  (1 <<  8)
+#define SP_CLR_SIG0        (1 <<  9)
+#define SP_SET_SIG0        (1 << 10)
+#define SP_CLR_SIG1        (1 << 11)
+#define SP_SET_SIG1        (1 << 12)
+#define SP_CLR_SIG2        (1 << 13)
+#define SP_SET_SIG2        (1 << 14)
+#define SP_CLR_SIG3        (1 << 15)
+#define SP_SET_SIG3        (1 << 16)
+#define SP_CLR_SIG4        (1 << 17)
+#define SP_SET_SIG4        (1 << 18)
+#define SP_CLR_SIG5        (1 << 19)
+#define SP_SET_SIG5        (1 << 20)
+#define SP_CLR_SIG6        (1 << 21)
+#define SP_SET_SIG6        (1 << 22)
+#define SP_CLR_SIG7        (1 << 23)
+#define SP_SET_SIG7        (1 << 24)
+
+/*
+ * SP_STATUS_REG: read bits
+ */
+#define SP_STATUS_HALT          (1 <<  0)
+#define SP_STATUS_BROKE         (1 <<  1)
+#define SP_STATUS_DMA_BUSY      (1 <<  2)
+#define SP_STATUS_DMA_FULL      (1 <<  3)
+#define SP_STATUS_IO_FULL       (1 <<  4)
+#define SP_STATUS_SSTEP         (1 <<  5)
+#define SP_STATUS_INTR_BREAK    (1 <<  6)
+#define SP_STATUS_SIG0          (1 <<  7)
+#define SP_STATUS_SIG1          (1 <<  8)
+#define SP_STATUS_SIG2          (1 <<  9)
+#define SP_STATUS_SIG3          (1 << 10)
+#define SP_STATUS_SIG4          (1 << 11)
+#define SP_STATUS_SIG5          (1 << 12)
+#define SP_STATUS_SIG6          (1 << 13)
+#define SP_STATUS_SIG7          (1 << 14)
+
+/**
+ * SP_STATUS_REG: use of SIG bits
+ */
+#define SP_CLR_YIELD            SP_CLR_SIG0
+#define SP_SET_YIELD            SP_SET_SIG0
+#define SP_STATUS_YIELD         SP_STATUS_SIG0
+#define SP_CLR_YIELDED          SP_CLR_SIG1
+#define SP_SET_YIELDED          SP_SET_SIG1
+#define SP_STATUS_YIELDED       SP_STATUS_SIG1
+#define SP_CLR_TASKDONE         SP_CLR_SIG2
+#define SP_SET_TASKDONE         SP_SET_SIG2
+#define SP_STATUS_TASKDONE      SP_STATUS_SIG2
+#define SP_CLR_RSPSIGNAL        SP_CLR_SIG3
+#define SP_SET_RSPSIGNAL        SP_SET_SIG3
+#define SP_STATUS_RSPSIGNAL     SP_STATUS_SIG3
+#define SP_CLR_CPUSIGNAL        SP_CLR_SIG4
+#define SP_SET_CPUSIGNAL        SP_SET_SIG4
+#define SP_STATUS_CPUSIGNAL     SP_STATUS_SIG4
+
 #define CHNL_ERR_NORESP     0x80    /* Bit 7 (Rx): No response error */
 #define CHNL_ERR_OVERRUN    0x40    /* Bit 6 (Rx): Overrun error */
 #define CHNL_ERR_FRAME      0x80    /* Bit 7 (Tx): Frame error */
diff --git a/include/PR/rsp.h b/include/PR/rsp.h
deleted file mode 100644
index 4ac58cf650..0000000000
--- a/include/PR/rsp.h
+++ /dev/null
@@ -1,58 +0,0 @@
-#ifndef PR_RSP_H
-#define PR_RSP_H
-
-#include "ultratypes.h"
-#include "libc/stddef.h"
-
-
-/* SP Status Flags */
-#define SP_STATUS_HALT        (1 <<  0)
-#define SP_STATUS_BROKE       (1 <<  1)
-#define SP_STATUS_DMA_BUSY    (1 <<  2)
-#define SP_STATUS_DMA_FULL    (1 <<  3)
-#define SP_STATUS_IO_FULL     (1 <<  4)
-#define SP_STATUS_SSTEP       (1 <<  5)
-#define SP_STATUS_INTR_BREAK  (1 <<  6)
-#define SP_STATUS_YIELD       (1 <<  7) // SIG0
-#define SP_STATUS_YIELDED     (1 <<  8) // SIG1
-#define SP_STATUS_TASKDONE    (1 <<  9) // SIG2
-#define SP_STATUS_SIG3        (1 << 10)
-#define SP_STATUS_SIG4        (1 << 11)
-#define SP_STATUS_SIG5        (1 << 12)
-#define SP_STATUS_SIG6        (1 << 13)
-#define SP_STATUS_SIG7        (1 << 14)
-
-#define SP_CLR_HALT        (1 <<  0)
-#define SP_SET_HALT        (1 <<  1)
-#define SP_CLR_BROKE       (1 <<  2)
-#define SP_CLR_INTR        (1 <<  3)
-#define SP_SET_INTR        (1 <<  4)
-#define SP_CLR_SSTEP       (1 <<  5)
-#define SP_SET_SSTEP       (1 <<  6)
-#define SP_CLR_INTR_BREAK  (1 <<  7)
-#define SP_SET_INTR_BREAK  (1 <<  8)
-#define SP_CLR_SIG0        (1 <<  9)
-#define SP_SET_SIG0        (1 << 10)
-#define SP_CLR_SIG1        (1 << 11)
-#define SP_SET_SIG1        (1 << 12)
-#define SP_CLR_SIG2        (1 << 13)
-#define SP_SET_SIG2        (1 << 14)
-#define SP_CLR_SIG3        (1 << 15)
-#define SP_SET_SIG3        (1 << 16)
-#define SP_CLR_SIG4        (1 << 17)
-#define SP_SET_SIG4        (1 << 18)
-#define SP_CLR_SIG5        (1 << 19)
-#define SP_SET_SIG5        (1 << 20)
-#define SP_CLR_SIG6        (1 << 21)
-#define SP_SET_SIG6        (1 << 22)
-#define SP_CLR_SIG7        (1 << 23)
-#define SP_SET_SIG7        (1 << 24)
-
-
-u32 __osSpGetStatus(void);
-void __osSpSetStatus(u32 data);
-s32 __osSpSetPc(u32 pc);
-s32 __osSpRawStartDma(s32 direction, u32 devAddr, void* dramAddr, size_t size);
-
-
-#endif
diff --git a/include/ultra64.h b/include/ultra64.h
index 0264c844a5..e6be91641d 100644
--- a/include/ultra64.h
+++ b/include/ultra64.h
@@ -15,7 +15,6 @@
 #include "PR/sptask.h"
 #include "PR/rcp.h"
 #include "PR/rdp.h"
-#include "PR/rsp.h"
 #include "PR/R4300.h"
 #include "PR/ucode.h"
 #include "PR/viint.h"
diff --git a/src/libultra/io/sirawread.c b/src/libultra/io/sirawread.c
index 7e3537603c..aca70e11b0 100644
--- a/src/libultra/io/sirawread.c
+++ b/src/libultra/io/sirawread.c
@@ -1,9 +1,9 @@
-#include "global.h"
+#include "ultra64.h"
 
 s32 __osSiRawReadIo(uintptr_t devAddr, u32* data) {
     if (__osSiDeviceBusy()) {
         return -1;
     }
-    *data = *(u32*)(devAddr | 0xA0000000);
+    *data = IO_READ(devAddr);
     return 0;
 }
diff --git a/src/libultra/io/sirawwrite.c b/src/libultra/io/sirawwrite.c
index 0f98b08c52..37749918bf 100644
--- a/src/libultra/io/sirawwrite.c
+++ b/src/libultra/io/sirawwrite.c
@@ -1,11 +1,11 @@
-#include "global.h"
+#include "ultra64.h"
 
 s32 __osSiRawWriteIo(uintptr_t devAddr, u32 data) {
     if (__osSiDeviceBusy() != 0) {
         return -1;
     }
 
-    *(u32*)(devAddr | 0xA0000000) = data;
+    IO_WRITE(devAddr, data);
 
     return 0;
 }
diff --git a/src/libultra/io/sp.c b/src/libultra/io/sp.c
index 3f7af40fa9..e1d95eeb88 100644
--- a/src/libultra/io/sp.c
+++ b/src/libultra/io/sp.c
@@ -1,4 +1,5 @@
-#include "global.h"
+#include "ultra64.h"
+#include "libc/stdbool.h"
 
 s32 __osSpDeviceBusy(void) {
     register u32 status = IO_READ(SP_STATUS_REG);
diff --git a/src/libultra/io/spgetstat.c b/src/libultra/io/spgetstat.c
index f448db4fb5..641261cf70 100644
--- a/src/libultra/io/spgetstat.c
+++ b/src/libultra/io/spgetstat.c
@@ -1,4 +1,4 @@
-#include "global.h"
+#include "ultra64.h"
 
 u32 __osSpGetStatus() {
     return IO_READ(SP_STATUS_REG);
diff --git a/src/libultra/io/sprawdma.c b/src/libultra/io/sprawdma.c
index 1e186af8f4..b09eff34dd 100644
--- a/src/libultra/io/sprawdma.c
+++ b/src/libultra/io/sprawdma.c
@@ -1,4 +1,4 @@
-#include "global.h"
+#include "ultra64.h"
 
 s32 __osSpRawStartDma(s32 direction, u32 devAddr, void* dramAddr, size_t size) {
     if (__osSpDeviceBusy()) {
diff --git a/src/libultra/io/spsetpc.c b/src/libultra/io/spsetpc.c
index 7582b5537f..2789428db8 100644
--- a/src/libultra/io/spsetpc.c
+++ b/src/libultra/io/spsetpc.c
@@ -1,4 +1,4 @@
-#include "global.h"
+#include "ultra64.h"
 
 s32 __osSpSetPc(u32 pc) {
     register u32 spStatus = IO_READ(SP_STATUS_REG);
diff --git a/src/libultra/io/spsetstat.c b/src/libultra/io/spsetstat.c
index 8ab21265f0..558b88fcf9 100644
--- a/src/libultra/io/spsetstat.c
+++ b/src/libultra/io/spsetstat.c
@@ -1,4 +1,4 @@
-#include "global.h"
+#include "ultra64.h"
 
 void __osSpSetStatus(u32 data) {
     IO_WRITE(SP_STATUS_REG, data);
diff --git a/src/libultra/io/sptask.c b/src/libultra/io/sptask.c
index c44da8fe7a..35ddeaf612 100644
--- a/src/libultra/io/sptask.c
+++ b/src/libultra/io/sptask.c
@@ -1,4 +1,4 @@
-#include "global.h"
+#include "ultra64.h"
 
 #define _osVirtualToPhysical(ptr)              \
     if (ptr != NULL) {                         \
diff --git a/src/libultra/io/sptaskyield.c b/src/libultra/io/sptaskyield.c
index ce0819b349..0d3285d819 100644
--- a/src/libultra/io/sptaskyield.c
+++ b/src/libultra/io/sptaskyield.c
@@ -1,5 +1,5 @@
-#include "global.h"
+#include "ultra64.h"
 
 void osSpTaskYield(void) {
-    __osSpSetStatus(0x400);
+    __osSpSetStatus(SP_SET_YIELD);
 }
diff --git a/src/libultra/io/sptaskyielded.c b/src/libultra/io/sptaskyielded.c
index 66b541921a..88c112305c 100644
--- a/src/libultra/io/sptaskyielded.c
+++ b/src/libultra/io/sptaskyielded.c
@@ -1,17 +1,17 @@
-#include "global.h"
+#include "ultra64.h"
 
 OSYieldResult osSpTaskYielded(OSTask* task) {
-    s32 status;
+    s32 status = __osSpGetStatus();
     OSYieldResult result;
-    status = __osSpGetStatus();
-    if (status & 0x100) {
-        result = 1;
+
+    if (status & SP_STATUS_YIELDED) {
+        result = OS_TASK_YIELDED;
     } else {
         result = 0;
     }
-    if (status & 0x80) {
+    if (status & SP_STATUS_YIELD) {
         task->t.flags |= result;
-        task->t.flags &= ~(2);
+        task->t.flags &= ~OS_TASK_DP_WAIT;
     }
     return result;
 }
diff --git a/src/libultra/io/vi.c b/src/libultra/io/vi.c
index cdcba49db9..117a2d70e1 100644
--- a/src/libultra/io/vi.c
+++ b/src/libultra/io/vi.c
@@ -1,6 +1,7 @@
-#include "global.h"
+#include "ultra64.h"
+#include "alignment.h"
 
-__OSViContext vi[2] = { 0 };
+__OSViContext vi[2] ALIGNED(8) = { 0 };
 __OSViContext* __osViCurr = &vi[0];
 __OSViContext* __osViNext = &vi[1];
 
diff --git a/src/libultra/io/viblack.c b/src/libultra/io/viblack.c
index 6b8fec9536..8b780d5389 100644
--- a/src/libultra/io/viblack.c
+++ b/src/libultra/io/viblack.c
@@ -1,4 +1,4 @@
-#include "global.h"
+#include "ultra64.h"
 
 void osViBlack(u8 active) {
     register u32 saveMask;
@@ -6,9 +6,9 @@ void osViBlack(u8 active) {
     saveMask = __osDisableInt();
 
     if (active) {
-        __osViNext->state |= 0x20;
+        __osViNext->state |= VI_STATE_BLACK;
     } else {
-        __osViNext->state &= ~0x20;
+        __osViNext->state &= ~VI_STATE_BLACK;
     }
 
     __osRestoreInt(saveMask);
diff --git a/src/libultra/io/viextendvstart.c b/src/libultra/io/viextendvstart.c
index ce9f718d01..b187f1418d 100644
--- a/src/libultra/io/viextendvstart.c
+++ b/src/libultra/io/viextendvstart.c
@@ -1,4 +1,4 @@
-#include "global.h"
+#include "ultra64.h"
 
 void osViExtendVStart(u32 a0) {
     __additional_scanline = a0;
diff --git a/src/libultra/io/vigetcurrcontext.c b/src/libultra/io/vigetcurrcontext.c
index 2b7de83417..3bb95fb4f7 100644
--- a/src/libultra/io/vigetcurrcontext.c
+++ b/src/libultra/io/vigetcurrcontext.c
@@ -1,4 +1,4 @@
-#include "global.h"
+#include "ultra64.h"
 
 __OSViContext* __osViGetCurrentContext(void) {
     return __osViCurr;
diff --git a/src/libultra/io/vigetcurrframebuf.c b/src/libultra/io/vigetcurrframebuf.c
index 8127a3f63a..f0caeb7b15 100644
--- a/src/libultra/io/vigetcurrframebuf.c
+++ b/src/libultra/io/vigetcurrframebuf.c
@@ -1,4 +1,4 @@
-#include "global.h"
+#include "ultra64.h"
 
 void* osViGetCurrentFramebuffer(void) {
     register u32 prevInt = __osDisableInt();
diff --git a/src/libultra/io/vigetnextframebuf.c b/src/libultra/io/vigetnextframebuf.c
index 21fd8ece7a..7e87c5f33d 100644
--- a/src/libultra/io/vigetnextframebuf.c
+++ b/src/libultra/io/vigetnextframebuf.c
@@ -1,4 +1,4 @@
-#include "global.h"
+#include "ultra64.h"
 
 void* osViGetNextFramebuffer(void) {
     register u32 saveMask;
diff --git a/src/libultra/io/vimgr.c b/src/libultra/io/vimgr.c
index ffeaec6305..f74d3d3adc 100644
--- a/src/libultra/io/vimgr.c
+++ b/src/libultra/io/vimgr.c
@@ -1,14 +1,16 @@
-#include "global.h"
+#include "ultra64.h"
 #include "PR/osint.h"
 #include "stack.h"
 #include "PR/osint.h"
+#include "libc/stdbool.h"
+#include "macros.h"
 
 OSThread viThread;
-STACK(sViStack, 0x1000);
-OSMesgQueue viEventQueue;
-OSMesg viEventBuf[6];
-OSIoMesg viRetraceMsg;
-OSIoMesg viCounterMsg;
+STACK(sViStack, OS_VIM_STACKSIZE) ALIGNED(16);
+OSMesgQueue viEventQueue ALIGNED(8);
+OSMesg viEventBuf[6] ALIGNED(8);
+OSIoMesg viRetraceMsg ALIGNED(8);
+OSIoMesg viCounterMsg ALIGNED(8);
 OSDevMgr __osViDevMgr = { 0 };
 u32 __additional_scanline = 0;
 
diff --git a/src/libultra/io/visetevent.c b/src/libultra/io/visetevent.c
index 3a14ccbc1b..701f41863d 100644
--- a/src/libultra/io/visetevent.c
+++ b/src/libultra/io/visetevent.c
@@ -1,4 +1,4 @@
-#include "global.h"
+#include "ultra64.h"
 
 void osViSetEvent(OSMesgQueue* mq, OSMesg m, u32 retraceCount) {
     register u32 saveMask = __osDisableInt();
diff --git a/src/libultra/io/visetmode.c b/src/libultra/io/visetmode.c
index 6953bf63b8..0e21f9a94a 100644
--- a/src/libultra/io/visetmode.c
+++ b/src/libultra/io/visetmode.c
@@ -1,4 +1,4 @@
-#include "global.h"
+#include "ultra64.h"
 
 void osViSetMode(OSViMode* modep) {
     register u32 saveMask;
@@ -6,7 +6,7 @@ void osViSetMode(OSViMode* modep) {
     saveMask = __osDisableInt();
 
     __osViNext->modep = modep;
-    __osViNext->state = 1;
+    __osViNext->state = VI_STATE_MODE_UPDATED;
     __osViNext->features = __osViNext->modep->comRegs.ctrl;
 
     __osRestoreInt(saveMask);
diff --git a/src/libultra/io/visetspecial.c b/src/libultra/io/visetspecial.c
index a5ef1220a4..758807b1bf 100644
--- a/src/libultra/io/visetspecial.c
+++ b/src/libultra/io/visetspecial.c
@@ -1,4 +1,4 @@
-#include "global.h"
+#include "ultra64.h"
 
 void osViSetSpecialFeatures(u32 func) {
     register u32 saveMask = __osDisableInt();
diff --git a/src/libultra/io/visetxscale.c b/src/libultra/io/visetxscale.c
index 0e2cf762d9..2a403cffd7 100644
--- a/src/libultra/io/visetxscale.c
+++ b/src/libultra/io/visetxscale.c
@@ -1,4 +1,4 @@
-#include "global.h"
+#include "ultra64.h"
 
 void osViSetXScale(f32 value) {
     register u32 nomValue;
@@ -8,10 +8,10 @@ void osViSetXScale(f32 value) {
 
     __osViNext->x.factor = value;
 
-    __osViNext->state |= 0x2;
+    __osViNext->state |= VI_STATE_XSCALE_UPDATED;
 
-    nomValue = __osViNext->modep->comRegs.xScale & 0xFFF;
-    __osViNext->x.scale = (u32)(__osViNext->x.factor * nomValue) & 0xFFF;
+    nomValue = __osViNext->modep->comRegs.xScale & VI_SCALE_MASK;
+    __osViNext->x.scale = (u32)(__osViNext->x.factor * nomValue) & VI_SCALE_MASK;
 
     __osRestoreInt(saveMask);
 }
diff --git a/src/libultra/io/visetyscale.c b/src/libultra/io/visetyscale.c
index 6ef85963df..0c4b734ba8 100644
--- a/src/libultra/io/visetyscale.c
+++ b/src/libultra/io/visetyscale.c
@@ -1,4 +1,4 @@
-#include "global.h"
+#include "ultra64.h"
 
 void osViSetYScale(f32 value) {
     register u32 saveMask;
@@ -7,7 +7,7 @@ void osViSetYScale(f32 value) {
 
     __osViNext->y.factor = value;
 
-    __osViNext->state |= 0x4;
+    __osViNext->state |= VI_STATE_YSCALE_UPDATED;
 
     __osRestoreInt(saveMask);
 }
diff --git a/src/libultra/io/viswapbuf.c b/src/libultra/io/viswapbuf.c
index c60918092a..dafce36f37 100644
--- a/src/libultra/io/viswapbuf.c
+++ b/src/libultra/io/viswapbuf.c
@@ -1,11 +1,11 @@
-#include "global.h"
+#include "ultra64.h"
 
 void osViSwapBuffer(void* frameBufPtr) {
 
     u32 saveMask = __osDisableInt();
 
     __osViNext->buffer = frameBufPtr;
-    __osViNext->state |= 0x10;
+    __osViNext->state |= VI_STATE_BUFFER_UPDATED;
 
     __osRestoreInt(saveMask);
 }
diff --git a/src/libultra/io/viswapcontext.c b/src/libultra/io/viswapcontext.c
index f6bf562e3c..528f04bea3 100644
--- a/src/libultra/io/viswapcontext.c
+++ b/src/libultra/io/viswapcontext.c
@@ -1,4 +1,4 @@
-#include "global.h"
+#include "ultra64.h"
 
 void __osViSwapContext(void) {
     register OSViMode* viMode;