diff --git a/src/xenia/gpu/command_processor.cc b/src/xenia/gpu/command_processor.cc
index 2361f3fd9..edb6138fa 100644
--- a/src/xenia/gpu/command_processor.cc
+++ b/src/xenia/gpu/command_processor.cc
@@ -512,7 +512,7 @@ uint32_t CommandProcessor::ExecutePacket(PacketArgs& args) {
           uint32_t value = READ_PTR();
           // Writeback initiator.
           WriteRegister(packet_ptr, XE_GPU_REG_VGT_EVENT_INITIATOR,
-                        initiator & 0x1F);
+                        initiator & 0x3F);
           uint32_t data_value;
           if ((initiator >> 31) & 0x1) {
             // Write counter (GPU vblank counter?).
diff --git a/src/xenia/gpu/graphics_system.cc b/src/xenia/gpu/graphics_system.cc
index c969e23d2..b1c0eb2d0 100644
--- a/src/xenia/gpu/graphics_system.cc
+++ b/src/xenia/gpu/graphics_system.cc
@@ -192,6 +192,9 @@ void GraphicsSystem::DispatchInterruptCallback(
     cpu = 2;
   }
 
+  XELOGGPU("Dispatching GPU interrupt at %.8X w/ mode %d on cpu %d",
+           interrupt_callback_, source, cpu);
+
   // NOTE: we may be executing in some random thread.
   if (!interrupt_callback_) {
     return;
diff --git a/src/xenia/gpu/xenos/register_table.inc b/src/xenia/gpu/xenos/register_table.inc
index c549e39a6..25a5890a0 100644
--- a/src/xenia/gpu/xenos/register_table.inc
+++ b/src/xenia/gpu/xenos/register_table.inc
@@ -18,12 +18,12 @@
 XE_GPU_REGISTER(0x01DD,  dword, SCRATCH_ADDR)
 XE_GPU_REGISTER(0x01DC,  dword, SCRATCH_UMSK)
 
-XE_GPU_REGISTER(0x0578,  dword, SCRATCH_REG0)
-XE_GPU_REGISTER(0x0579,  dword, SCRATCH_REG1)
+XE_GPU_REGISTER(0x0578,  dword, SCRATCH_REG0)  // interrupt sync
+XE_GPU_REGISTER(0x0579,  dword, SCRATCH_REG1)  // present interval
 XE_GPU_REGISTER(0x057A,  dword, SCRATCH_REG2)
 XE_GPU_REGISTER(0x057B,  dword, SCRATCH_REG3)
-XE_GPU_REGISTER(0x057C,  dword, SCRATCH_REG4)
-XE_GPU_REGISTER(0x057D,  dword, SCRATCH_REG5)
+XE_GPU_REGISTER(0x057C,  dword, CALLBACK_ADDRESS)
+XE_GPU_REGISTER(0x057D,  dword, CALLBACK_CONTEXT)
 XE_GPU_REGISTER(0x057E,  dword, SCRATCH_REG6)
 XE_GPU_REGISTER(0x057F,  dword, SCRATCH_REG7)
 
diff --git a/src/xenia/kernel/xboxkrnl_threading.cc b/src/xenia/kernel/xboxkrnl_threading.cc
index 4a7805f13..a727d8f45 100644
--- a/src/xenia/kernel/xboxkrnl_threading.cc
+++ b/src/xenia/kernel/xboxkrnl_threading.cc
@@ -1177,6 +1177,8 @@ SHIM_CALL KeInsertQueueDpc_shim(PPCContext* ppc_state, KernelState* state) {
   uint32_t arg1 = SHIM_GET_ARG_32(1);
   uint32_t arg2 = SHIM_GET_ARG_32(2);
 
+  assert_always("DPC does not dispatch yet; going to hang!");
+
   XELOGD("KeInsertQueueDpc(%.8X, %.8X, %.8X)", dpc_ptr, arg1, arg2);
 
   uint32_t list_entry_ptr = dpc_ptr + 4;