diff --git a/src/gu/Makefile.am b/src/gu/Makefile.am
index f0389db4..80fd80e7 100644
--- a/src/gu/Makefile.am
+++ b/src/gu/Makefile.am
@@ -12,10 +12,11 @@ CFLAGS =  @PSPSDK_CFLAGS@
 libpspguincludedir = @PSPSDK_INCLUDEDIR@
 libpspguinclude_HEADERS = pspgu.h
 
-lib_LIBRARIES = libpspgu.a
+lib_LIBRARIES = libpspgu.a libpspgud.a
 
 noinst_HEADERS = guInternal.h
 
+# Regular library (no debug assertions)
 libpspgu_a_SOURCES = \
 	guInternal.c \
 	sceGuAlphaFunc.c \
@@ -112,3 +113,7 @@ libpspgu_a_SOURCES = \
 	sceGuViewport.c \
 	vram.c
 
+# Debug library (with debug assertions)
+libpspgud_a_SOURCES = $(libpspgu_a_SOURCES)
+libpspgud_a_CFLAGS = $(CFLAGS) -DGU_DEBUG
+
diff --git a/src/gu/guInternal.c b/src/gu/guInternal.c
index 1c70f45e..2b88e79f 100644
--- a/src/gu/guInternal.c
+++ b/src/gu/guInternal.c
@@ -19,5 +19,5 @@ int gu_display_on;
 int gu_call_mode;
 int gu_states;
 GuDrawBuffer gu_draw_buffer;
-unsigned int* gu_object_stack[32];
+unsigned int* gu_object_stack[GU_OBJECT_STACK_SIZE];
 int gu_object_stack_depth;
diff --git a/src/gu/guInternal.h b/src/gu/guInternal.h
index 019b5aa7..a8942537 100644
--- a/src/gu/guInternal.h
+++ b/src/gu/guInternal.h
@@ -11,6 +11,13 @@
 
 #include "pspgu.h"
 
+#ifdef GU_DEBUG
+#include <assert.h>
+#include <stdio.h>
+#endif
+
+#define GU_OBJECT_STACK_SIZE 32
+
 typedef void (*GuCallback)(int);
 
 typedef struct
diff --git a/src/gu/sceGuAlphaFunc.c b/src/gu/sceGuAlphaFunc.c
index 4baee0b0..4d6b1b38 100644
--- a/src/gu/sceGuAlphaFunc.c
+++ b/src/gu/sceGuAlphaFunc.c
@@ -10,6 +10,12 @@
 
 void sceGuAlphaFunc(int func, int value, int mask)
 {
+#ifdef GU_DEBUG
+	printf("sceGuAlphaFunc(%d, %d, %d);\n", func, value, mask);
+	assert(gu_init && "GU not initialized");
+	assert(func >= GU_NEVER && func <= GU_GEQUAL && "Invalid alpha function");
+#endif
+
 	int arg = func | ((value & 0xff) << 8) | ((mask & 0xff) << 16);
 	sendCommandi(ALPHA_TEST, arg);
 }
diff --git a/src/gu/sceGuAmbient.c b/src/gu/sceGuAmbient.c
index 2211201c..633e7310 100644
--- a/src/gu/sceGuAmbient.c
+++ b/src/gu/sceGuAmbient.c
@@ -10,6 +10,11 @@
 
 void sceGuAmbient(unsigned int color)
 {
+#ifdef GU_DEBUG
+	printf("sceGuAmbient(%08X);\n", color);
+	assert(gu_init && "GU not initialized");
+#endif
+
 	sendCommandi(AMBIENT_LIGHT_COLOR,(color));
 	sendCommandi(AMBIENT_LIGHT_ALPHA,(color >> 24));
 }
diff --git a/src/gu/sceGuAmbientColor.c b/src/gu/sceGuAmbientColor.c
index 54b66d20..2a625098 100644
--- a/src/gu/sceGuAmbientColor.c
+++ b/src/gu/sceGuAmbientColor.c
@@ -10,6 +10,11 @@
 
 void sceGuAmbientColor(unsigned int color)
 {
+#ifdef GU_DEBUG
+	printf("sceGuAmbientColor(0x%08X);\n", color);
+	assert(gu_init && "GU not initialized");
+#endif
+
 	sendCommandi(AMBIENT_COLOR, color);
 	sendCommandi(AMBIENT_ALPHA, color >> 24);
 }
diff --git a/src/gu/sceGuBeginObject.c b/src/gu/sceGuBeginObject.c
index 2907b962..0a9aa478 100644
--- a/src/gu/sceGuBeginObject.c
+++ b/src/gu/sceGuBeginObject.c
@@ -10,6 +10,13 @@
 
 void sceGuBeginObject(int vertex_type, int count, const void *indices, const void *vertices)
 {
+#ifdef GU_DEBUG
+	printf("sceGuBeginObject(%d, %d, %p, %p);\n", vertex_type, count, indices, vertices);
+	assert(gu_init && "GU not initialized");
+	assert(count > 0 && count <= 255 && (count % 8) == 0 && "Invalid vertex count - must be positive, <= 65535, and multiple of 8");
+	assert(gu_object_stack_depth < GU_OBJECT_STACK_SIZE && "Object stack overflow");
+#endif
+
 	if (vertex_type)
 		sendCommandi(VERTEX_TYPE, vertex_type);
 
diff --git a/src/gu/sceGuBlendFunc.c b/src/gu/sceGuBlendFunc.c
index af66d5d8..55baedbe 100644
--- a/src/gu/sceGuBlendFunc.c
+++ b/src/gu/sceGuBlendFunc.c
@@ -10,6 +10,14 @@
 
 void sceGuBlendFunc(int op, int src, int dest, unsigned int srcfix, unsigned int destfix)
 {
+#ifdef GU_DEBUG
+	printf("sceGuBlendFunc(%d, %d, %d, 0x%08X, 0x%08X);\n", op, src, dest, srcfix, destfix);
+	assert(gu_init && "GU not initialized");
+	assert(op >= GU_ADD && op <= GU_ABS && "Invalid blend operation");
+	assert(src >= GU_OTHER_COLOR && src <= GU_FIX && "Invalid source blend factor");
+	assert(dest >= GU_OTHER_COLOR && dest <= GU_FIX && "Invalid destination blend factor");
+#endif
+
 	sendCommandi(BLEND_MODE, src | (dest << 4) | (op << 8));
 	sendCommandi(BLEND_FIXED_A, srcfix);
 	sendCommandi(BLEND_FIXED_B, destfix);
diff --git a/src/gu/sceGuBoneMatrix.c b/src/gu/sceGuBoneMatrix.c
index dc3ec15a..770a4ddd 100644
--- a/src/gu/sceGuBoneMatrix.c
+++ b/src/gu/sceGuBoneMatrix.c
@@ -10,6 +10,12 @@
 
 void sceGuBoneMatrix(unsigned int index, const ScePspFMatrix4 *matrix)
 {
+#ifdef GU_DEBUG
+	printf("sceGuBoneMatrix(%d, %p);\n", index, matrix);
+	assert(gu_init && "GU not initialized");
+	assert(index < 8 && "Invalid bone matrix index");
+#endif
+
 	unsigned int offset = ((index << 1) + index) << 2; // 3*4 matrix
 	unsigned int i, j;
 	const float *fmatrix = (const float *)matrix;
diff --git a/src/gu/sceGuCallList.c b/src/gu/sceGuCallList.c
index 7633c1b2..ff9268e9 100644
--- a/src/gu/sceGuCallList.c
+++ b/src/gu/sceGuCallList.c
@@ -10,6 +10,11 @@
 
 int sceGuCallList(const void *list)
 {
+#ifdef GU_DEBUG
+	printf("sceGuCallList(%p);\n", list);
+	assert(gu_init && "GU not initialized");
+#endif
+
 	int res;
 	unsigned int list_addr = (unsigned int)list;
 
diff --git a/src/gu/sceGuCallMode.c b/src/gu/sceGuCallMode.c
index 7721d5c2..1f48d7d1 100644
--- a/src/gu/sceGuCallMode.c
+++ b/src/gu/sceGuCallMode.c
@@ -10,5 +10,11 @@
 
 void sceGuCallMode(int mode)
 {
+#ifdef GU_DEBUG
+	printf("sceGuCallMode(%d);\n", mode);
+	assert(gu_init && "GU not initialized");
+	assert(mode >= GU_CALL_NORMAL && mode <= GU_CALL_SIGNAL && "Invalid call mode");
+#endif
+
 	gu_call_mode = mode;
 }
diff --git a/src/gu/sceGuClear.c b/src/gu/sceGuClear.c
index 4ae8190c..dd1bd4c2 100644
--- a/src/gu/sceGuClear.c
+++ b/src/gu/sceGuClear.c
@@ -10,6 +10,13 @@
 
 void sceGuClear(int flags)
 {
+#ifdef GU_DEBUG
+	printf("sceGuClear(%d);\n", flags);
+	assert(gu_init && "GU not initialized");
+	assert(flags >= 0 && "Invalid clear flags");
+	assert((flags & ~(GU_COLOR_BUFFER_BIT | GU_STENCIL_BUFFER_BIT | GU_DEPTH_BUFFER_BIT | GU_FAST_CLEAR_BIT)) == 0 && "Invalid clear flags");
+#endif
+
 	GuContext *context = &gu_contexts[gu_curr_context];
 	unsigned int filter;
 	struct Vertex
diff --git a/src/gu/sceGuClearColor.c b/src/gu/sceGuClearColor.c
index 1655c55e..b7e36a80 100644
--- a/src/gu/sceGuClearColor.c
+++ b/src/gu/sceGuClearColor.c
@@ -10,6 +10,11 @@
 
 void sceGuClearColor(unsigned int color)
 {
+#ifdef GU_DEBUG
+	printf("sceGuClearColor(0x%08X);\n", color);
+	assert(gu_init && "GU not initialized");
+#endif
+
 	GuContext* context = &gu_contexts[gu_curr_context];
 	context->clear_color = color;
 }
diff --git a/src/gu/sceGuClearDepth.c b/src/gu/sceGuClearDepth.c
index 3b61831e..843e4b78 100644
--- a/src/gu/sceGuClearDepth.c
+++ b/src/gu/sceGuClearDepth.c
@@ -10,6 +10,12 @@
 
 void sceGuClearDepth(unsigned int depth)
 {
+#ifdef GU_DEBUG
+	printf("sceGuClearDepth(%u);\n", depth);
+	assert(gu_init && "GU not initialized");
+	assert(depth <= 65535 && "Invalid depth value");
+#endif
+
 	GuContext* context = &gu_contexts[gu_curr_context];
 	context->clear_depth = depth;
 }
diff --git a/src/gu/sceGuClearStencil.c b/src/gu/sceGuClearStencil.c
index 25272898..a871f2cd 100644
--- a/src/gu/sceGuClearStencil.c
+++ b/src/gu/sceGuClearStencil.c
@@ -10,6 +10,29 @@
 
 void sceGuClearStencil(unsigned int stencil)
 {
+#ifdef GU_DEBUG
+	printf("sceGuClearStencil(%u);\n", stencil);
+	assert(gu_init && "GU not initialized");
+	switch (gu_draw_buffer.pixel_size)
+	{
+	case GU_PSM_8888:
+		assert(stencil <= 255 && "Invalid stencil value for GU_PSM_8888");
+		break;
+	case GU_PSM_4444:
+		assert(stencil <= 15 && "Invalid stencil value for GU_PSM_4444");
+		break;
+	case GU_PSM_5551:
+		assert(stencil <= 1 && "Invalid stencil value for GU_PSM_5551");
+		break;
+	case GU_PSM_5650:
+		assert(0 && "Stencil not supported for GU_PSM_5650");
+		break;	
+	default:
+		assert(0 && "Invalid pixel format");
+		break;
+	}
+#endif
+
 	GuContext* context = &gu_contexts[gu_curr_context];
 	context->clear_stencil = stencil;
 }
diff --git a/src/gu/sceGuClutLoad.c b/src/gu/sceGuClutLoad.c
index 7748891e..1509b263 100644
--- a/src/gu/sceGuClutLoad.c
+++ b/src/gu/sceGuClutLoad.c
@@ -10,6 +10,12 @@
 
 void sceGuClutLoad(int num_blocks, const void *cbp)
 {
+#ifdef GU_DEBUG
+	printf("sceGuClutLoad(%d, %p);\n", num_blocks, cbp);
+	assert(gu_init && "GU not initialized");
+	assert(num_blocks > 0 && num_blocks <= 65535 && "Invalid number of CLUT blocks");
+#endif
+
 	sendCommandi(CLUT_BUF_PTR, ((unsigned int)cbp));
 	sendCommandi(CLUT_BUF_WIDTH, (((unsigned int)cbp) >> 8) & 0xf0000);
 	sendCommandi(CLUT_LOAD, num_blocks);
diff --git a/src/gu/sceGuClutMode.c b/src/gu/sceGuClutMode.c
index 0fddf3f5..ec512f65 100644
--- a/src/gu/sceGuClutMode.c
+++ b/src/gu/sceGuClutMode.c
@@ -10,6 +10,12 @@
 
 void sceGuClutMode(unsigned int cpsm, unsigned int shift, unsigned int mask, unsigned int csa)
 {
+#ifdef GU_DEBUG
+	printf("sceGuClutMode(%08X, %08X, %08X, %08X);\n", cpsm, shift, mask, csa);
+	assert(gu_init && "GU not initialized");
+	assert(cpsm >= GU_PSM_5650 && cpsm <= GU_PSM_8888 && "Invalid CLUT pixel format");
+#endif
+
 	unsigned int argument = (cpsm) | (shift << 2) | (mask << 8) | (csa << 16);
 	sendCommandi(CLUT_FORMAT, argument);
 }
diff --git a/src/gu/sceGuColor.c b/src/gu/sceGuColor.c
index 946bd39e..ae19dd48 100644
--- a/src/gu/sceGuColor.c
+++ b/src/gu/sceGuColor.c
@@ -10,5 +10,9 @@
 
 void sceGuColor(unsigned int color)
 {
+#ifdef GU_DEBUG
+	assert(gu_init && "GU not initialized");
+#endif
+
 	sceGuMaterial(GU_AMBIENT | GU_DIFFUSE | GU_SPECULAR, color);
 }
diff --git a/src/gu/sceGuColorFunc.c b/src/gu/sceGuColorFunc.c
index 30e8c12a..981779b6 100644
--- a/src/gu/sceGuColorFunc.c
+++ b/src/gu/sceGuColorFunc.c
@@ -10,6 +10,12 @@
 
 void sceGuColorFunc(int func, unsigned int color, unsigned int mask)
 {
+#ifdef GU_DEBUG
+	printf("sceGuColorFunc(%d, 0x%08X, 0x%08X);\n", func, color, mask);
+	assert(gu_init && "GU not initialized");
+	assert(func >= GU_NEVER && func <= GU_NOTEQUAL && "Invalid color function");
+#endif
+
 	sendCommandi(COLOR_TEST, func & 0x03);
 	sendCommandi(COLOR_REF, color);
 	sendCommandi(COLOR_TESTMASK, mask);
diff --git a/src/gu/sceGuColorMaterial.c b/src/gu/sceGuColorMaterial.c
index bbb48f7b..1f056227 100644
--- a/src/gu/sceGuColorMaterial.c
+++ b/src/gu/sceGuColorMaterial.c
@@ -10,5 +10,11 @@
 
 void sceGuColorMaterial(int components)
 {
+#ifdef GU_DEBUG
+	printf("sceGuColorMaterial(%d);\n", components);
+	assert(gu_init && "GU not initialized");
+	assert((components >= 0) && ((components & ~(GU_AMBIENT | GU_DIFFUSE | GU_SPECULAR)) == 0) && "Invalid material components");
+#endif
+
 	sendCommandi(MATERIAL_COLOR, components);
 }
diff --git a/src/gu/sceGuContinue.c b/src/gu/sceGuContinue.c
index e6197170..ba016101 100644
--- a/src/gu/sceGuContinue.c
+++ b/src/gu/sceGuContinue.c
@@ -6,9 +6,13 @@
  * Copyright (c) 2005 Jesper Svennevid
  */
 
-#include "pspge.h"
+#include "guInternal.h"
 
 int sceGuContinue(void)
 {
+#ifdef GU_DEBUG
+	printf("sceGuContinue();\n");
+	assert(gu_init && "GU not initialized");
+#endif
 	return sceGeContinue();
 }
diff --git a/src/gu/sceGuCopyImage.c b/src/gu/sceGuCopyImage.c
index 51eef944..ae877b48 100644
--- a/src/gu/sceGuCopyImage.c
+++ b/src/gu/sceGuCopyImage.c
@@ -10,6 +10,20 @@
 
 void sceGuCopyImage(int psm, int sx, int sy, int width, int height, int srcw, void *src, int dx, int dy, int destw, void *dest)
 {
+#ifdef GU_DEBUG
+	printf("sceGuCopyImage(%d, %d, %d, %d, %d, %d, %p, %d, %d, %d, %p);\n", psm, sx, sy, width, height, srcw, src, dx, dy, destw, dest);
+	assert(gu_init && "GU not initialized");
+	assert(psm >= GU_PSM_5650 && psm <= GU_PSM_8888 && "Invalid pixel format");
+	assert(width > 0 && width <= 1023 && "Invalid width");
+	assert(height > 0 && height <= 1023 && "Invalid height");
+	assert(srcw > 8 && srcw <= 1024 && (srcw & 0x7) == 0 && "Invalid source width, must be multiple of 8");
+	assert(destw > 8 && destw <= 1024 && (destw & 0x7) == 0 && "Invalid destination width, must be multiple of 8");
+	assert(sx >= 0 && sx < 1023 && "Invalid source X");
+	assert(sy >= 0 && sy < 1023 && "Invalid source Y");
+	assert(dx >= 0 && dx < 1023 && "Invalid destination X");
+	assert(dy >= 0 && dy < 1023 && "Invalid destination Y");
+#endif
+
 	sendCommandi(TRANSFER_SRC, ((unsigned int)src));
 	sendCommandi(TRANSFER_SRC_W, ((((unsigned int)src) & 0xff000000) >> 8) | srcw);
 	sendCommandi(TRANSFER_SRC_OFFSET, (sy << 10) | sx);
diff --git a/src/gu/sceGuDepthBuffer.c b/src/gu/sceGuDepthBuffer.c
index 76829d04..79993986 100644
--- a/src/gu/sceGuDepthBuffer.c
+++ b/src/gu/sceGuDepthBuffer.c
@@ -10,6 +10,13 @@
 
 void sceGuDepthBuffer(void *zbp, int zbw)
 {
+#ifdef GU_DEBUG
+	printf("sceGuDepthBuffer(%p, %d);\n", zbp, zbw);
+	assert(gu_init && "GU not initialized");
+	assert((zbw & 0x1FFF) == 0 && "Depth buffer pointer must be 8192-byte aligned");
+	assert(zbw > 64 && zbw <= 1024 && (zbw & 0x3F) == 0 && "Invalid depth buffer width, must be multiple of 64");
+#endif
+
 	sendCommandi(Z_BUF_PTR, ((unsigned int)zbp));
 	sendCommandi(Z_BUF_WIDTH, ((((unsigned int)zbp) & 0xff000000) >> 8) | zbw);
 	
diff --git a/src/gu/sceGuDepthFunc.c b/src/gu/sceGuDepthFunc.c
index f410d429..4f55c47c 100644
--- a/src/gu/sceGuDepthFunc.c
+++ b/src/gu/sceGuDepthFunc.c
@@ -10,5 +10,11 @@
 
 void sceGuDepthFunc(int function)
 {
+#ifdef GU_DEBUG
+	printf("sceGuDepthFunc(%d);\n", function);
+	assert(gu_init && "GU not initialized");
+	assert(function >= GU_NEVER && function <= GU_GEQUAL && "Invalid depth function");
+#endif
+
 	sendCommandi(Z_TEST, function);
 }
diff --git a/src/gu/sceGuDepthMask.c b/src/gu/sceGuDepthMask.c
index a4046b60..413ece44 100644
--- a/src/gu/sceGuDepthMask.c
+++ b/src/gu/sceGuDepthMask.c
@@ -10,5 +10,11 @@
 
 void sceGuDepthMask(int mask)
 {
+#ifdef GU_DEBUG
+	printf("sceGuDepthMask(%d);\n", mask);
+	assert(gu_init && "GU not initialized");
+	assert((mask == 0 || mask == 1) && "Invalid depth mask");
+#endif
+
 	sendCommandi(Z_MASK, mask);
 }
diff --git a/src/gu/sceGuDepthOffset.c b/src/gu/sceGuDepthOffset.c
index e794be17..a9336784 100644
--- a/src/gu/sceGuDepthOffset.c
+++ b/src/gu/sceGuDepthOffset.c
@@ -10,6 +10,11 @@
 
 void sceGuDepthOffset(unsigned int offset)
 {
+#ifdef GU_DEBUG
+	printf("sceGuDepthOffset(%08X);\n", offset);
+	assert(gu_init && "GU not initialized");
+#endif
+
 	GuContext* context = &gu_contexts[gu_curr_context];
 	context->depth_offset = offset;
 
diff --git a/src/gu/sceGuDepthRange.c b/src/gu/sceGuDepthRange.c
index e5642a22..8a3e2748 100644
--- a/src/gu/sceGuDepthRange.c
+++ b/src/gu/sceGuDepthRange.c
@@ -10,6 +10,13 @@
 
 void sceGuDepthRange(int near, int far)
 {
+#ifdef GU_DEBUG
+	printf("sceGuDepthRange(%d, %d);\n", near, far);
+	assert(gu_init && "GU not initialized");
+	assert(near >= 0 && near <= 65535 && "Invalid near plane");
+	assert(far >= 0 && far <= 65535 && "Invalid far plane");
+#endif
+
         GuContext *context = &gu_contexts[gu_curr_context];
 
         unsigned int max = (unsigned int)near + (unsigned int)far;
diff --git a/src/gu/sceGuDisable.c b/src/gu/sceGuDisable.c
index c978e0a6..985d6629 100644
--- a/src/gu/sceGuDisable.c
+++ b/src/gu/sceGuDisable.c
@@ -10,6 +10,12 @@
 
 void sceGuDisable(int state)
 {
+#ifdef GU_DEBUG
+	printf("sceGuDisable(%d);\n", state);
+	assert(gu_init && "GU not initialized");
+	assert(state >= 0 && state < GU_MAX_STATUS && "Invalid state");
+#endif
+
 	switch (state)
 	{
 	case GU_ALPHA_TEST:
diff --git a/src/gu/sceGuDispBuffer.c b/src/gu/sceGuDispBuffer.c
index ea6306f3..cd87bd10 100644
--- a/src/gu/sceGuDispBuffer.c
+++ b/src/gu/sceGuDispBuffer.c
@@ -13,6 +13,13 @@
 
 void sceGuDispBuffer(int width, int height, void *dispbp, int dispbw)
 {
+#ifdef GU_DEBUG
+	printf("sceGuDispBuffer(%d, %d, %p, %d);\n", width, height, dispbp, dispbw);
+	assert(gu_init && "GU not initialized");
+	assert(((unsigned int)dispbp & 0x1F) == 0 && "Display buffer pointer must be 32-byte aligned");
+	assert(dispbw >= 64 && dispbw <= 1024 && (dispbw & 0x3F) == 0 && "Display buffer width must be multiple of 64");
+#endif
+
 	gu_draw_buffer.width = width;
 	gu_draw_buffer.height = height;
 	gu_draw_buffer.disp_buffer = dispbp;
diff --git a/src/gu/sceGuDisplay.c b/src/gu/sceGuDisplay.c
index 90987c4e..b24cdd3a 100644
--- a/src/gu/sceGuDisplay.c
+++ b/src/gu/sceGuDisplay.c
@@ -13,6 +13,12 @@
 
 int sceGuDisplay(int state)
 {
+#ifdef GU_DEBUG
+	printf("sceGuDisplay(%d);\n", state);
+	assert(gu_init && "GU not initialized");
+	assert((state == GU_TRUE || state == GU_FALSE) && "Invalid display state");
+#endif
+
 	if (state == GU_TRUE)
 		sceDisplaySetFrameBuf((void *)((unsigned int)ge_edram_address + (unsigned int)gu_draw_buffer.disp_buffer), gu_draw_buffer.frame_width, gu_draw_buffer.pixel_size, PSP_DISPLAY_SETBUF_NEXTVSYNC);
 	else
diff --git a/src/gu/sceGuDrawArray.c b/src/gu/sceGuDrawArray.c
index 2dcdb872..89ef84d2 100644
--- a/src/gu/sceGuDrawArray.c
+++ b/src/gu/sceGuDrawArray.c
@@ -10,6 +10,13 @@
 
 void sceGuDrawArray(int prim, int vtype, int count, const void *indices, const void *vertices)
 {
+#ifdef GU_DEBUG
+	printf("sceGuDrawArray(%d, %d, %d, %p, %p);\n", prim, vtype, count, indices, vertices);
+	assert(gu_init && "GU not initialized");
+	assert(count > 0 && count <= 65535 && "Invalid vertex count");
+	assert(prim >= GU_POINTS && prim <= GU_SPRITES && "Invalid primitive type");
+#endif
+
   if (vtype)
     sendCommandi(VERTEX_TYPE, vtype);
 
diff --git a/src/gu/sceGuDrawArrayN.c b/src/gu/sceGuDrawArrayN.c
index dd5ecc45..0e5298a4 100644
--- a/src/gu/sceGuDrawArrayN.c
+++ b/src/gu/sceGuDrawArrayN.c
@@ -10,6 +10,14 @@
 
 void sceGuDrawArrayN(int primitive_type, int vertex_type, int vcount, int primcount, const void *indices, const void *vertices)
 {
+#ifdef GU_DEBUG
+	printf("sceGuDrawArrayN(%d, %d, %d, %d, %p, %p);\n", primitive_type, vertex_type, vcount, primcount, indices, vertices);
+	assert(gu_init && "GU not initialized");
+	assert(vcount > 0 && vcount <= 65535 && "Invalid vertex count");
+	assert(primcount > 0 && primcount <= 65535 && "Invalid primitive count");
+	assert(primitive_type >= GU_POINTS && primitive_type <= GU_TRIANGLE_FAN && "Invalid primitive type");
+#endif
+
 	if (vertex_type)
 		sendCommandi(VERTEX_TYPE, vertex_type);
 
diff --git a/src/gu/sceGuDrawBezier.c b/src/gu/sceGuDrawBezier.c
index 0c32f51a..ac479c91 100644
--- a/src/gu/sceGuDrawBezier.c
+++ b/src/gu/sceGuDrawBezier.c
@@ -10,6 +10,13 @@
 
 void sceGuDrawBezier(int vertex_type, int ucount, int vcount, const void *indices, const void *vertices)
 {
+#ifdef GU_DEBUG
+	printf("sceGuDrawBezier(%d, %d, %d, %p, %p);\n", vertex_type, ucount, vcount, indices, vertices);
+	assert(gu_init && "GU not initialized");
+	assert(ucount > 1 && ucount <= 255 && (ucount % 3) == 1 && "Invalid U count, must be 3*N+1");
+	assert(vcount > 1 && vcount <= 255 && (vcount % 3) == 1 && "Invalid V count, must be 3*N+1");
+#endif
+
   if (vertex_type)
     sendCommandi(VERTEX_TYPE, vertex_type);
 
diff --git a/src/gu/sceGuDrawBuffer.c b/src/gu/sceGuDrawBuffer.c
index bb7e85d9..3b584228 100644
--- a/src/gu/sceGuDrawBuffer.c
+++ b/src/gu/sceGuDrawBuffer.c
@@ -10,6 +10,15 @@
 
 void sceGuDrawBuffer(int psm, void *fbp, int frame_width)
 {
+#ifdef GU_DEBUG
+	printf("sceGuDrawBuffer(%d, %p, %d);\n", psm, fbp, frame_width);
+	assert(gu_init && "GU not initialized");
+	assert(((unsigned int)fbp & 0x1FFF) == 0 && "Frame buffer pointer must be 8192-byte aligned");
+	assert(frame_width >= 64 && frame_width <= 1024 && "Frame width must be between 64 and 1024");
+	assert((frame_width & 63) == 0 && "Frame width must be a multiple of 64");
+	assert(psm >= GU_PSM_5650 && psm <= GU_PSM_8888 && "Invalid pixel format");
+#endif
+
 	gu_draw_buffer.pixel_size = psm;
 	gu_draw_buffer.frame_width = frame_width;
 	gu_draw_buffer.frame_buffer = fbp;
diff --git a/src/gu/sceGuDrawBufferList.c b/src/gu/sceGuDrawBufferList.c
index 351ad37f..03eb122e 100644
--- a/src/gu/sceGuDrawBufferList.c
+++ b/src/gu/sceGuDrawBufferList.c
@@ -10,6 +10,14 @@
 
 void sceGuDrawBufferList(int psm, void *fbp, int fbw)
 {
+#ifdef GU_DEBUG
+	printf("sceGuDrawBufferList(%d, %p, %d);\n", psm, fbp, fbw);
+	assert(gu_init && "GU not initialized");
+	assert(((unsigned int)fbp & 0x1FFF) == 0 && "Frame buffer pointer must be 8192-byte aligned");
+	assert(fbw >= 64 && fbw <= 1024 && (fbw & 0x3F) == 0 && "Frame buffer width must be multiple of 64");
+	assert(psm >= GU_PSM_5650 && psm <= GU_PSM_8888 && "Invalid pixel format");
+#endif
+
 	sendCommandi(FRAMEBUF_PIX_FORMAT, psm);
 	sendCommandi(FRAME_BUF_PTR, (unsigned int)fbp);
 	sendCommandi(FRAME_BUF_WIDTH, ((((unsigned int)fbp) & 0xff000000) >> 8) | fbw);
diff --git a/src/gu/sceGuDrawSpline.c b/src/gu/sceGuDrawSpline.c
index 92e0e70a..1c1d71f7 100644
--- a/src/gu/sceGuDrawSpline.c
+++ b/src/gu/sceGuDrawSpline.c
@@ -10,6 +10,15 @@
 
 void sceGuDrawSpline(int vertex_type, int ucount, int vcount, int uedge, int vedge, const void *indices, const void *vertices)
 {
+#ifdef GU_DEBUG
+	printf("sceGuDrawSpline(%d, %d, %d, %d, %d, %p, %p);\n", vertex_type, ucount, vcount, uedge, vedge, indices, vertices);
+	assert(gu_init && "GU not initialized");
+	assert(ucount >= 4 && ucount <= 255 && "Invalid U count - must be between 4 and 255");
+	assert(vcount >= 4 && vcount <= 255 && "Invalid V count - must be between 4 and 255");
+	assert(uedge >= 0 && uedge <= 3 && "Invalid U edge");
+	assert(vedge >= 0 && vedge <= 3 && "Invalid V edge");
+#endif
+
   if (vertex_type)
     sendCommandi(VERTEX_TYPE, vertex_type);
 
diff --git a/src/gu/sceGuEnable.c b/src/gu/sceGuEnable.c
index 84e1c33c..b006a14a 100644
--- a/src/gu/sceGuEnable.c
+++ b/src/gu/sceGuEnable.c
@@ -10,6 +10,12 @@
 
 void sceGuEnable(int state)
 {
+#ifdef GU_DEBUG
+	printf("sceGuEnable(%d);\n", state);
+	assert(gu_init && "GU not initialized");
+	assert(state >= 0 && state < GU_MAX_STATUS && "Invalid enable state");
+#endif
+
 	switch (state)
 	{
 	case GU_ALPHA_TEST:
diff --git a/src/gu/sceGuEndObject.c b/src/gu/sceGuEndObject.c
index 0f3db5d3..df6f6642 100644
--- a/src/gu/sceGuEndObject.c
+++ b/src/gu/sceGuEndObject.c
@@ -12,6 +12,12 @@
 
 int sceGuEndObject(void)
 {
+#ifdef GU_DEBUG
+	printf("sceGuEndObject();\n");
+	assert(gu_init && "GU not initialized");
+	assert(gu_object_stack_depth > 0 && "Object stack underflow");
+#endif
+
 	int res;
 
 	gu_object_stack_depth--;
diff --git a/src/gu/sceGuFinishId.c b/src/gu/sceGuFinishId.c
index 2d63ca8c..8df0d21d 100644
--- a/src/gu/sceGuFinishId.c
+++ b/src/gu/sceGuFinishId.c
@@ -12,6 +12,11 @@
 
 int sceGuFinishId(unsigned int id)
 {
+#ifdef GU_DEBUG
+	printf("sceGuFinishId(%08X);\n", id);
+	assert(gu_init && "GU not initialized");
+#endif
+
 	int ret;
 	int intr;
 
diff --git a/src/gu/sceGuFog.c b/src/gu/sceGuFog.c
index 184b1f8b..75773eb5 100644
--- a/src/gu/sceGuFog.c
+++ b/src/gu/sceGuFog.c
@@ -10,6 +10,14 @@
 
 void sceGuFog(float near, float far, unsigned int color)
 {
+#ifdef GU_DEBUG
+	printf("sceGuFog(%f, %f, %08X);\n", near, far, color);
+	assert(gu_init && "GU not initialized");
+	assert(near >= 0.0f && "Invalid fog near value");
+	assert(far > near && "Fog far must be greater than near");
+	assert(far <= 65535.0f && "Fog far value too large");
+#endif
+
 	float distance = far - near;
 
 	if (distance)
diff --git a/src/gu/sceGuFrontFace.c b/src/gu/sceGuFrontFace.c
index e2aede14..66d86270 100644
--- a/src/gu/sceGuFrontFace.c
+++ b/src/gu/sceGuFrontFace.c
@@ -10,5 +10,11 @@
 
 void sceGuFrontFace(int order)
 {
+#ifdef GU_DEBUG
+	printf("sceGuFrontFace(%d);\n", order);
+	assert(gu_init && "GU not initialized");
+	assert((order == GU_CW || order == GU_CCW) && "Invalid front face order");
+#endif
+
 	sendCommandi(CULL, order ? 0 : 1);
 }
diff --git a/src/gu/sceGuInit.c b/src/gu/sceGuInit.c
index 4cb47323..c5e4c512 100644
--- a/src/gu/sceGuInit.c
+++ b/src/gu/sceGuInit.c
@@ -308,15 +308,27 @@ void callbackSig(int id, void *arg)
 
 int sceGuInit(void)
 {
+#ifdef GU_DEBUG
+	printf("sceGuInit();\n");
+	assert(!gu_init && "GU already initialized");
+#endif
+
 	int res;
 	PspGeCallbackData callback;
 
 	ge_edram_address = sceGeEdramGetAddr();
+#ifdef GU_DEBUG
+	assert(ge_edram_address != NULL && "Failed to get EDRAM address");
+#endif
+
 	sceGuResetGlobalVariables();
 
 	res = sceKernelCreateEventFlag("SceGuSignal", PSP_EVENT_WAITMULTIPLE, 3, 0);
 	if (res < 0)
 	{
+#ifdef GU_DEBUG
+		printf("Failed to create event flag: %d\n", res);
+#endif
 		return res;
 	}
 	gu_settings.kernel_event_flag = res;
@@ -328,6 +340,9 @@ int sceGuInit(void)
 	res = sceGeSetCallback(&callback);
 	if (res < 0)
 	{
+#ifdef GU_DEBUG
+		printf("Failed to set GE callback: %d\n", res);
+#endif
 		sceKernelDeleteEventFlag(gu_settings.kernel_event_flag);
 		gu_settings.kernel_event_flag = -1;
 		return res;
@@ -338,6 +353,9 @@ int sceGuInit(void)
 	res = sceGeListEnQueue((void *)((unsigned int)ge_init_list & 0x1fffffff), NULL, gu_settings.ge_callback_id, NULL);
 	if (res < 0)
 	{
+#ifdef GU_DEBUG
+		printf("Failed to enqueue GE list: %d\n", res);
+#endif
 		sceKernelDeleteEventFlag(gu_settings.kernel_event_flag);
 		sceGeUnsetCallback(gu_settings.ge_callback_id);
 		gu_settings.ge_callback_id = -1;
@@ -352,5 +370,6 @@ int sceGuInit(void)
 	gu_settings.swapBuffersCallback = NULL;
 	gu_settings.swapBuffersBehaviour = PSP_DISPLAY_SETBUF_NEXTHSYNC;
 
+	gu_init = 1;
 	return 0;
 }
diff --git a/src/gu/sceGuLight.c b/src/gu/sceGuLight.c
index dbe5d3d2..685e0b00 100644
--- a/src/gu/sceGuLight.c
+++ b/src/gu/sceGuLight.c
@@ -14,6 +14,14 @@
 
 void sceGuLight(int light, int type, int components, const ScePspFVector3 *position)
 {
+#ifdef GU_DEBUG
+	printf("sceGuLight(%d, %d, %d, %p);\n", light, type, components, position);
+	assert(gu_init && "GU not initialized");
+	assert(light >= 0 && light <= 3 && "Invalid light index");
+	assert(type >= GU_DIRECTIONAL && type <= GU_SPOTLIGHT && "Invalid light type");
+	assert(components >= GU_AMBIENT && components <= GU_DIFFUSE_AND_SPECULAR && "Invalid light components");
+#endif
+
 	int offset = light * 3;
 	int ltype;
 
diff --git a/src/gu/sceGuLightAtt.c b/src/gu/sceGuLightAtt.c
index 6a8abe9a..020c9575 100644
--- a/src/gu/sceGuLightAtt.c
+++ b/src/gu/sceGuLightAtt.c
@@ -10,6 +10,12 @@
 
 void sceGuLightAtt(int light, float atten0, float atten1, float atten2)
 {
+#ifdef GU_DEBUG
+	printf("sceGuLightAtt(%d, %f, %f, %f);\n", light, atten0, atten1, atten2);
+	assert(gu_init && "GU not initialized");
+	assert(light >= 0 && light <= 3 && "Invalid light index");
+#endif
+
 	int offset = light * 3;
 
 	sendCommandf(LIGHT0_CONSTANT_ATTEN + offset, atten0);
diff --git a/src/gu/sceGuLightColor.c b/src/gu/sceGuLightColor.c
index 0734f2bf..44cee530 100644
--- a/src/gu/sceGuLightColor.c
+++ b/src/gu/sceGuLightColor.c
@@ -10,6 +10,12 @@
 
 void sceGuLightColor(int light, int component, unsigned int color)
 {
+#ifdef GU_DEBUG
+	printf("sceGuLightColor(%d, %d, 0x%08X);\n", light, component, color);
+	assert(gu_init && "GU not initialized");
+	assert(light >= 0 && light <= 3 && "Invalid light index");
+	assert(component >= GU_AMBIENT && component <= GU_DIFFUSE_AND_SPECULAR && "Invalid light component");
+#endif
 
 	int offset = light * 3;
 
diff --git a/src/gu/sceGuLightMode.c b/src/gu/sceGuLightMode.c
index 1059972d..29f18093 100644
--- a/src/gu/sceGuLightMode.c
+++ b/src/gu/sceGuLightMode.c
@@ -10,5 +10,11 @@
 
 void sceGuLightMode(int mode)
 {
+#ifdef GU_DEBUG
+	printf("sceGuLightMode(%d);\n", mode);
+	assert(gu_init && "GU not initialized");
+	assert(mode >= GU_SINGLE_COLOR && mode <= GU_SEPARATE_SPECULAR_COLOR && "Invalid light mode");
+#endif
+
 	sendCommandi(LIGHT_MODE, mode);
 }
diff --git a/src/gu/sceGuLightSpot.c b/src/gu/sceGuLightSpot.c
index 7283455e..d3a0c899 100644
--- a/src/gu/sceGuLightSpot.c
+++ b/src/gu/sceGuLightSpot.c
@@ -9,7 +9,13 @@
 #include "guInternal.h"
 
 void sceGuLightSpot(int light, const ScePspFVector3 *direction, float exponent, float cutoff)
-{	
+{
+#ifdef GU_DEBUG
+	printf("sceGuLightSpot(%d, %p, %f, %f);\n", light, direction, exponent, cutoff);
+	assert(gu_init && "GU not initialized");
+	assert(light >= 0 && light <= 3 && "Invalid light index");
+#endif
+
 	int offset = light * 3;
 	sendCommandf(LIGHT0_EXPONENT_ATTEN + light, exponent);
 	sendCommandf(LIGHT0_CUTOFF_ATTEN + light, cutoff);
diff --git a/src/gu/sceGuLogicalOp.c b/src/gu/sceGuLogicalOp.c
index d524ff26..6de97998 100644
--- a/src/gu/sceGuLogicalOp.c
+++ b/src/gu/sceGuLogicalOp.c
@@ -10,5 +10,11 @@
 
 void sceGuLogicalOp(int op)
 {
+#ifdef GU_DEBUG
+	printf("sceGuLogicalOp(%d);\n", op);
+	assert(gu_init && "GU not initialized");
+	assert(op >= GU_CLEAR && op <= GU_SET && "Invalid logical operation");
+#endif
+
 	sendCommandi(LOGIC_OP, op & 0x0f);
 }
diff --git a/src/gu/sceGuMaterial.c b/src/gu/sceGuMaterial.c
index 241d6030..3b54648f 100644
--- a/src/gu/sceGuMaterial.c
+++ b/src/gu/sceGuMaterial.c
@@ -10,6 +10,13 @@
 
 void sceGuMaterial(int mode, int color)
 {
+#ifdef GU_DEBUG
+	printf("sceGuMaterial(%d, %08X);\n", mode, color);
+	assert(gu_init && "GU not initialized");
+	assert(mode >= 0 && "Invalid material mode");
+	assert((mode & ~(GU_AMBIENT | GU_DIFFUSE | GU_SPECULAR)) == 0 && "Invalid material mode flags");
+#endif
+
 	if (mode & GU_AMBIENT) {
 		sendCommandi(AMBIENT_COLOR, color);
 		sendCommandi(AMBIENT_ALPHA, color >> 24);
diff --git a/src/gu/sceGuModelColor.c b/src/gu/sceGuModelColor.c
index 04814cfa..74bdd8e6 100644
--- a/src/gu/sceGuModelColor.c
+++ b/src/gu/sceGuModelColor.c
@@ -10,6 +10,11 @@
 
 void sceGuModelColor(unsigned int emissive, unsigned int ambient, unsigned int diffuse, unsigned int specular)
 {
+#ifdef GU_DEBUG
+	printf("sceGuModelColor(%08X, %08X, %08X, %08X);\n", emissive, ambient, diffuse, specular);
+	assert(gu_init && "GU not initialized");
+#endif
+
 	sendCommandi(MATERIAL_EMISSIVE, emissive);
 	sendCommandi(MATERIAL_DIFFUSE, diffuse);
 	sendCommandi(AMBIENT_COLOR, ambient);
diff --git a/src/gu/sceGuMorphWeight.c b/src/gu/sceGuMorphWeight.c
index 626c38f7..f08e1c0c 100644
--- a/src/gu/sceGuMorphWeight.c
+++ b/src/gu/sceGuMorphWeight.c
@@ -10,5 +10,11 @@
 
 void sceGuMorphWeight(int index, float weight)
 {
+#ifdef GU_DEBUG
+	printf("sceGuMorphWeight(%d, %f);\n", index, weight);
+	assert(gu_init && "GU not initialized");
+	assert(index >= 0 && index <= 7 && "Invalid morph weight index");
+#endif
+
 	sendCommandf(MORPH_WEIGHT0 + index, weight);
 }
diff --git a/src/gu/sceGuOffset.c b/src/gu/sceGuOffset.c
index b3dec082..5b28fe66 100644
--- a/src/gu/sceGuOffset.c
+++ b/src/gu/sceGuOffset.c
@@ -10,6 +10,13 @@
 
 void sceGuOffset(unsigned int x, unsigned int y)
 {
+#ifdef GU_DEBUG
+	printf("sceGuOffset(%08X, %08X);\n", x, y);
+	assert(gu_init && "GU not initialized");
+	assert(x < 4096 && "X offset too large");
+	assert(y < 4096 && "Y offset too large");
+#endif
+
 	sendCommandi(OFFSET_X, x << 4);
 	sendCommandi(OFFSET_Y, y << 4);
 }
diff --git a/src/gu/sceGuPatchDivide.c b/src/gu/sceGuPatchDivide.c
index 8002d3ce..9333a025 100644
--- a/src/gu/sceGuPatchDivide.c
+++ b/src/gu/sceGuPatchDivide.c
@@ -10,5 +10,12 @@
 
 void sceGuPatchDivide(unsigned int ulevel, unsigned int vlevel)
 {
+#ifdef GU_DEBUG
+	printf("sceGuPatchDivide(%08X, %08X);\n", ulevel, vlevel);
+	assert(gu_init && "GU not initialized");
+	assert(ulevel >= 1 && ulevel <= 64 && "Invalid U level - must be between 1 and 64");
+	assert(vlevel >= 1 && vlevel <= 64 && "Invalid V level - must be between 1 and 64");
+#endif
+
 	sendCommandi(PATCH_DIVISION, (vlevel << 8) | ulevel);
 }
diff --git a/src/gu/sceGuPatchFrontFace.c b/src/gu/sceGuPatchFrontFace.c
index 54552ead..65d9873d 100644
--- a/src/gu/sceGuPatchFrontFace.c
+++ b/src/gu/sceGuPatchFrontFace.c
@@ -10,5 +10,11 @@
 
 void sceGuPatchFrontFace(unsigned int mode)
 {
+#ifdef GU_DEBUG
+	printf("sceGuPatchFrontFace(%u);\n", mode);
+	assert(gu_init && "GU not initialized");
+	assert((mode == GU_CW || mode == GU_CCW) && "Invalid patch front face mode");
+#endif
+
 	sendCommandi(PATCH_FACING, mode);
 }
diff --git a/src/gu/sceGuPatchPrim.c b/src/gu/sceGuPatchPrim.c
index ba0d4285..b3ea1ba9 100644
--- a/src/gu/sceGuPatchPrim.c
+++ b/src/gu/sceGuPatchPrim.c
@@ -10,6 +10,12 @@
 
 void sceGuPatchPrim(int prim)
 {
+#ifdef GU_DEBUG
+	printf("sceGuPatchPrim(%d);\n", prim);
+	assert(gu_init && "GU not initialized");
+	assert((prim == GU_POINTS || prim == GU_LINE_STRIP || prim == GU_TRIANGLE_STRIP) && "Invalid patch primitive");
+#endif
+
 	switch (prim)
 	{
 	case GU_POINTS:
diff --git a/src/gu/sceGuPixelMask.c b/src/gu/sceGuPixelMask.c
index 606ff667..72c772cb 100644
--- a/src/gu/sceGuPixelMask.c
+++ b/src/gu/sceGuPixelMask.c
@@ -10,6 +10,11 @@
 
 void sceGuPixelMask(unsigned int mask)
 {
+#ifdef GU_DEBUG
+	printf("sceGuPixelMask(%08X);\n", mask);
+	assert(gu_init && "GU not initialized");
+#endif
+
 	sendCommandi(MASK_COLOR, mask);
 	sendCommandi(MASK_ALPHA, mask >> 24);
 }
diff --git a/src/gu/sceGuScissor.c b/src/gu/sceGuScissor.c
index 8f76a8a5..0d09b156 100644
--- a/src/gu/sceGuScissor.c
+++ b/src/gu/sceGuScissor.c
@@ -10,6 +10,14 @@
 
 void sceGuScissor(int x, int y, int w, int h)
 {
+#ifdef GU_DEBUG
+	printf("sceGuScissor(%d, %d, %d, %d);\n", x, y, w, h);
+	assert(gu_init && "GU not initialized");
+	assert(w > 0 && h > 0 && "Invalid scissor dimensions");
+	assert(x >= 0 && y >= 0 && "Invalid scissor position");
+	assert(x + w <= 480 && y + h <= 272 && "Scissor region too large");
+#endif
+
 	GuContext *context = &gu_contexts[gu_curr_context];
 
 	context->scissor_start[0] = x;
diff --git a/src/gu/sceGuSendCommandf.c b/src/gu/sceGuSendCommandf.c
index 47a17558..f4bba0dc 100644
--- a/src/gu/sceGuSendCommandf.c
+++ b/src/gu/sceGuSendCommandf.c
@@ -10,5 +10,9 @@
 
 void sceGuSendCommandf(int cmd, float argument)
 {
+#ifdef GU_DEBUG
+	assert(gu_init && "GU not initialized");
+#endif
+
 	sendCommandf(cmd,argument);
 }
diff --git a/src/gu/sceGuSendCommandi.c b/src/gu/sceGuSendCommandi.c
index 3e7b0765..0262c87a 100644
--- a/src/gu/sceGuSendCommandi.c
+++ b/src/gu/sceGuSendCommandi.c
@@ -10,5 +10,9 @@
 
 void sceGuSendCommandi(int cmd, int argument)
 {
+#ifdef GU_DEBUG
+	assert(gu_init && "GU not initialized");
+#endif
+
 	sendCommandi(cmd, argument);
 }
diff --git a/src/gu/sceGuSendList.c b/src/gu/sceGuSendList.c
index 71b781b5..0e333c91 100644
--- a/src/gu/sceGuSendList.c
+++ b/src/gu/sceGuSendList.c
@@ -13,6 +13,12 @@
 
 int sceGuSendList(int mode, const void *list, PspGeContext *context)
 {
+#ifdef GU_DEBUG
+	printf("sceGuSendList(%d, %p, %p);\n", mode, list, context);
+	assert(gu_init && "GU not initialized");
+	assert((mode == GU_HEAD || mode == GU_TAIL) && "Invalid list mode");
+#endif
+
 	PspGeListArgs args;
 	int list_id;
 	int callback;
diff --git a/src/gu/sceGuSetAllStatus.c b/src/gu/sceGuSetAllStatus.c
index f25b4bd3..6c85f8c6 100644
--- a/src/gu/sceGuSetAllStatus.c
+++ b/src/gu/sceGuSetAllStatus.c
@@ -10,6 +10,11 @@
 
 void sceGuSetAllStatus(int status)
 {
+#ifdef GU_DEBUG
+	printf("sceGuSetAllStatus(%d);\n", status);
+	assert(gu_init && "GU not initialized");
+#endif
+
 	unsigned int i;
 	for (i = 0; i < GU_MAX_STATUS; ++i)
 	{
diff --git a/src/gu/sceGuSetCallback.c b/src/gu/sceGuSetCallback.c
index e75607ab..71643de9 100644
--- a/src/gu/sceGuSetCallback.c
+++ b/src/gu/sceGuSetCallback.c
@@ -10,6 +10,12 @@
 
 void *sceGuSetCallback(int signal, GuCallback callback)
 {
+#ifdef GU_DEBUG
+	printf("sceGuSetCallback(%d, %p);\n", signal, callback);
+	assert(gu_init && "GU not initialized");
+	assert((signal == GU_CALLBACK_SIGNAL || signal == GU_CALLBACK_FINISH) && "Invalid signal");
+#endif
+
 	GuCallback old_callback = NULL;
 
 	switch (signal)
diff --git a/src/gu/sceGuSetDither.c b/src/gu/sceGuSetDither.c
index ace9d695..54013172 100644
--- a/src/gu/sceGuSetDither.c
+++ b/src/gu/sceGuSetDither.c
@@ -10,6 +10,11 @@
 
 void sceGuSetDither(const ScePspIMatrix4 *matrix)
 {
+#ifdef GU_DEBUG
+	printf("sceGuSetDither(%p);\n", matrix);
+	assert(gu_init && "GU not initialized");
+#endif
+
 	sendCommandi(DITH0, (matrix->x.x & 0x0f) | ((matrix->x.y & 0x0f) << 4) | ((matrix->x.z & 0x0f) << 8) | ((matrix->x.w & 0x0f) << 12));
 	sendCommandi(DITH1, (matrix->y.x & 0x0f) | ((matrix->y.y & 0x0f) << 4) | ((matrix->y.z & 0x0f) << 8) | ((matrix->y.w & 0x0f) << 12));
 	sendCommandi(DITH2, (matrix->z.x & 0x0f) | ((matrix->z.y & 0x0f) << 4) | ((matrix->z.z & 0x0f) << 8) | ((matrix->z.w & 0x0f) << 12));
diff --git a/src/gu/sceGuSetMatrix.c b/src/gu/sceGuSetMatrix.c
index 76a6d658..4657565a 100644
--- a/src/gu/sceGuSetMatrix.c
+++ b/src/gu/sceGuSetMatrix.c
@@ -10,6 +10,12 @@
 
 void sceGuSetMatrix(int type, const ScePspFMatrix4 *matrix)
 {
+#ifdef GU_DEBUG
+	printf("sceGuSetMatrix(%d, %p);\n", type, matrix);
+	assert(gu_init && "GU not initialized");
+	assert(type >= GU_PROJECTION && type <= GU_TEXTURE && "Invalid matrix type");
+#endif
+
 	unsigned int i, j;
 	const float *fmatrix = (const float *)matrix;
 
diff --git a/src/gu/sceGuSetStatus.c b/src/gu/sceGuSetStatus.c
index b127f032..9a42ce4c 100644
--- a/src/gu/sceGuSetStatus.c
+++ b/src/gu/sceGuSetStatus.c
@@ -10,6 +10,13 @@
 
 void sceGuSetStatus(int state, int status)
 {
+#ifdef GU_DEBUG
+	printf("sceGuSetStatus(%d, %d);\n", state, status);
+	assert(gu_init && "GU not initialized");
+	assert(state >= 0 && state < GU_MAX_STATUS && "Invalid state");
+	assert((status == 0 || status == 1) && "Invalid status");
+#endif
+
 	if (status)
 		sceGuEnable(state);
 	else
diff --git a/src/gu/sceGuShadeModel.c b/src/gu/sceGuShadeModel.c
index faef3007..19c9383b 100644
--- a/src/gu/sceGuShadeModel.c
+++ b/src/gu/sceGuShadeModel.c
@@ -10,5 +10,11 @@
 
 void sceGuShadeModel(int mode)
 {
+#ifdef GU_DEBUG
+	printf("sceGuShadeModel(%d);\n", mode);
+	assert(gu_init && "GU not initialized");
+	assert((mode == GU_FLAT || mode == GU_SMOOTH) && "Invalid shade model");
+#endif
+
 	sendCommandi(SHADE_MODE, mode);
 }
diff --git a/src/gu/sceGuSignal.c b/src/gu/sceGuSignal.c
index 58dbc531..07d12cab 100644
--- a/src/gu/sceGuSignal.c
+++ b/src/gu/sceGuSignal.c
@@ -10,6 +10,13 @@
 
 void sceGuSignal(int mode, int id)
 {
+#ifdef GU_DEBUG
+	printf("sceGuSignal(%d, %d);\n", mode, id);
+	assert(gu_init && "GU not initialized");
+	assert(mode >= GU_SIGNAL_WAIT && mode <= GU_SIGNAL_PAUSE && "Invalid signal mode");
+	assert(id >= 0 && id <= 65535 && "Invalid signal ID, must be between 0 and 65535");
+#endif
+
 	sendCommandi(SIGNAL, ((mode & 0xff) << 16) | (id & 0xffff));
 	sendCommandi(END, 0);
 
diff --git a/src/gu/sceGuSpecular.c b/src/gu/sceGuSpecular.c
index f8d9c6cd..3245a989 100644
--- a/src/gu/sceGuSpecular.c
+++ b/src/gu/sceGuSpecular.c
@@ -10,5 +10,10 @@
 
 void sceGuSpecular(float power) // specular power
 {
+#ifdef GU_DEBUG
+	printf("sceGuSpecular(%f);\n", power);
+	assert(gu_init && "GU not initialized");
+#endif
+
 	sendCommandf(MATERIAL_SPECULAR_COEF, power);
 }
diff --git a/src/gu/sceGuStart.c b/src/gu/sceGuStart.c
index e4c8cf4f..ab405d56 100644
--- a/src/gu/sceGuStart.c
+++ b/src/gu/sceGuStart.c
@@ -14,6 +14,12 @@
 
 int sceGuStart(int ctype, void *list)
 {
+#ifdef GU_DEBUG
+	printf("sceGuStart(%d, %p);\n", ctype, list);
+	assert(gu_init && "GU not initialized");
+	assert((ctype == GU_DIRECT || ctype == GU_CALL || ctype == GU_SEND) && "Invalid context type");
+#endif
+
 	int intr;
 	GuContext *context = &gu_contexts[ctype];
 	unsigned int *local_list = (unsigned int *)(((unsigned int)list) | 0x40000000);
diff --git a/src/gu/sceGuStencilFunc.c b/src/gu/sceGuStencilFunc.c
index d065053b..9a9a76be 100644
--- a/src/gu/sceGuStencilFunc.c
+++ b/src/gu/sceGuStencilFunc.c
@@ -10,5 +10,14 @@
 
 void sceGuStencilFunc(int func, int ref, int mask)
 {
-	sendCommandi(STENCIL_TEST, func | ((ref & 0xff) << 8) | ((mask & 0xff) << 16));
+#ifdef GU_DEBUG
+	printf("sceGuStencilFunc(%d, %d, %d);\n", func, ref, mask);
+	assert(gu_init && "GU not initialized");
+	assert(func >= GU_NEVER && func <= GU_GEQUAL && "Invalid stencil function");
+	assert(ref >= 0 && ref <= 255 && "Invalid stencil reference");
+	assert(mask >= 0 && mask <= 255 && "Invalid stencil mask");
+#endif
+
+	int arg = func | ((ref & 0xff) << 8) | ((mask & 0xff) << 16);
+	sendCommandi(STENCIL_TEST, arg);
 }
diff --git a/src/gu/sceGuStencilOp.c b/src/gu/sceGuStencilOp.c
index e144cce4..0e705c3d 100644
--- a/src/gu/sceGuStencilOp.c
+++ b/src/gu/sceGuStencilOp.c
@@ -10,5 +10,14 @@
 
 void sceGuStencilOp(int fail, int zfail, int zpass)
 {
-	sendCommandi(STENCIL_OP, fail | (zfail << 8) | (zpass << 16));
+#ifdef GU_DEBUG
+	printf("sceGuStencilOp(%d, %d, %d);\n", fail, zfail, zpass);
+	assert(gu_init && "GU not initialized");
+	assert(fail >= GU_KEEP && fail <= GU_DECR && "Invalid stencil fail operation");
+	assert(zfail >= GU_KEEP && zfail <= GU_DECR && "Invalid stencil zfail operation");
+	assert(zpass >= GU_KEEP && zpass <= GU_DECR && "Invalid stencil zpass operation");
+#endif
+
+	int arg = fail | (zfail << 8) | (zpass << 16);
+	sendCommandi(STENCIL_OP, arg);
 }
diff --git a/src/gu/sceGuSwapBuffers.c b/src/gu/sceGuSwapBuffers.c
index b10dade0..d6ceb95d 100644
--- a/src/gu/sceGuSwapBuffers.c
+++ b/src/gu/sceGuSwapBuffers.c
@@ -13,6 +13,11 @@
 
 void *sceGuSwapBuffers(void)
 {
+#ifdef GU_DEBUG
+	printf("sceGuSwapBuffers();\n");
+	assert(gu_init && "GU not initialized");
+#endif
+
 	if (gu_settings.swapBuffersCallback)
 	{
 		gu_settings.swapBuffersCallback(&gu_draw_buffer.disp_buffer, &gu_draw_buffer.frame_buffer);
diff --git a/src/gu/sceGuSync.c b/src/gu/sceGuSync.c
index d23a753f..4b90c853 100644
--- a/src/gu/sceGuSync.c
+++ b/src/gu/sceGuSync.c
@@ -13,6 +13,13 @@
 
 int sceGuSync(int mode, int what)
 {
+#ifdef GU_DEBUG
+	printf("sceGuSync(%d, %d);\n", mode, what);
+	assert(gu_init && "GU not initialized");
+	assert((mode == GU_SYNC_FINISH || mode == GU_SYNC_LIST || mode == GU_SYNC_SEND || mode == GU_SYNC_SIGNAL || mode == GU_SYNC_DONE) && "Invalid sync mode");
+	assert((what == GU_SYNC_WAIT || what == GU_SYNC_NOWAIT) && "Invalid sync what");	
+#endif
+
 	switch (mode)
 	{
 	case GU_SYNC_FINISH:
diff --git a/src/gu/sceGuTerm.c b/src/gu/sceGuTerm.c
index 6e9c6900..96c9e1aa 100644
--- a/src/gu/sceGuTerm.c
+++ b/src/gu/sceGuTerm.c
@@ -13,6 +13,13 @@
 
 void sceGuTerm(void)
 {
+#ifdef GU_DEBUG
+	printf("sceGuTerm();\n");
+	assert(gu_init && "GU not initialized");
+	assert(gu_settings.kernel_event_flag >= 0 && "Invalid kernel event flag");
+	assert(gu_settings.ge_callback_id >= 0 && "Invalid GE callback ID");
+#endif
+
 	sceKernelDeleteEventFlag(gu_settings.kernel_event_flag);
 	sceGeUnsetCallback(gu_settings.ge_callback_id);
 }
diff --git a/src/gu/sceGuTexEnvColor.c b/src/gu/sceGuTexEnvColor.c
index 2bdf1cac..5f143a8c 100644
--- a/src/gu/sceGuTexEnvColor.c
+++ b/src/gu/sceGuTexEnvColor.c
@@ -10,5 +10,10 @@
 
 void sceGuTexEnvColor(unsigned int color)
 {
+#ifdef GU_DEBUG
+	printf("sceGuTexEnvColor(0x%08X);\n", color);
+	assert(gu_init && "GU not initialized");
+#endif
+
 	sendCommandi(TEX_ENV_COLOR, color);
 }
diff --git a/src/gu/sceGuTexFilter.c b/src/gu/sceGuTexFilter.c
index 31b2d281..07899fea 100644
--- a/src/gu/sceGuTexFilter.c
+++ b/src/gu/sceGuTexFilter.c
@@ -10,5 +10,13 @@
 
 void sceGuTexFilter(int min, int mag)
 {
-	sendCommandi(TEX_FILTER, (mag << 8) | min);
+#ifdef GU_DEBUG
+	printf("sceGuTexFilter(%d, %d);\n", min, mag);
+	assert(gu_init && "GU not initialized");
+	assert(min >= GU_NEAREST && min <= GU_LINEAR_MIPMAP_LINEAR && "Invalid minification filter");
+	assert(mag >= GU_NEAREST && mag <= GU_LINEAR && "Invalid magnification filter");
+#endif
+
+	int arg = min | (mag << 8);
+	sendCommandi(TEX_FILTER, arg);
 }
diff --git a/src/gu/sceGuTexFlush.c b/src/gu/sceGuTexFlush.c
index 51f39796..837de922 100644
--- a/src/gu/sceGuTexFlush.c
+++ b/src/gu/sceGuTexFlush.c
@@ -10,5 +10,10 @@
 
 void sceGuTexFlush(void)
 {
+#ifdef GU_DEBUG
+	printf("sceGuTexFlush();\n");
+	assert(gu_init && "GU not initialized");
+#endif
+
 	sendCommandi(TEX_FLUSH, 0);
 }
diff --git a/src/gu/sceGuTexFunc.c b/src/gu/sceGuTexFunc.c
index 0ffa11b6..cfb12f56 100644
--- a/src/gu/sceGuTexFunc.c
+++ b/src/gu/sceGuTexFunc.c
@@ -10,8 +10,14 @@
 
 void sceGuTexFunc(int tfx, int tcc)
 {
-	GuContext *context = &gu_contexts[gu_curr_context];
-	context->texture_function = (tcc << 8) | tfx;
+#ifdef GU_DEBUG
+	printf("sceGuTexFunc(%d, %d);\n", tfx, tcc);
+	assert(gu_init && "GU not initialized");
+	assert(tfx >= GU_TFX_MODULATE && tfx <= GU_TFX_ADD && "Invalid texture function");
+	assert(tcc >= GU_TCC_RGB && tcc <= GU_TCC_RGBA && "Invalid texture color component");
+#endif
 
-	sendCommandi(TEX_FUNC, ((tcc << 8) | tfx) | context->fragment_2x);
+	GuContext *context = &gu_contexts[gu_curr_context];
+	context->texture_function = tfx | (tcc << 8);
+	sendCommandi(TEX_FUNC, context->texture_function | context->fragment_2x);
 }
diff --git a/src/gu/sceGuTexImage.c b/src/gu/sceGuTexImage.c
index 756bd64e..1dfed07e 100644
--- a/src/gu/sceGuTexImage.c
+++ b/src/gu/sceGuTexImage.c
@@ -15,6 +15,18 @@ static inline int getExp(int val)
 
 void sceGuTexImage(int mipmap, int width, int height, int tbw, const void *tbp)
 {
+#ifdef GU_DEBUG
+	printf("sceGuTexImage(%d, %d, %d, %d, %p);\n", mipmap, width, height, tbw, tbp);
+	assert(gu_init && "GU not initialized");
+	assert(((unsigned int)tbp & 0xF) == 0 && "Texture buffer pointer must be 16-byte aligned");
+	assert(mipmap >= 0 && mipmap <= 7 && "Invalid mipmap level");
+	assert(width >= 1 && width <= 512 && "Invalid texture width");
+	assert(height >= 1 && height <= 512 && "Invalid texture height");
+	assert(tbw >= 1 && tbw <= 1024 && "Invalid texture buffer width");
+	assert((width & (width - 1)) == 0 && "Texture width must be power of 2");
+	assert((height & (height - 1)) == 0 && "Texture height must be power of 2");
+#endif
+
 	GECommand texAddr = (GECommand)(TEX_ADDR0 + mipmap);
 	GECommand texBufWidth = (GECommand)(TEX_BUF_WIDTH0 + mipmap);
 	GECommand texSize = (GECommand)(TEX_SIZE0 + mipmap);
diff --git a/src/gu/sceGuTexLevelMode.c b/src/gu/sceGuTexLevelMode.c
index a2d15d66..0566bfce 100644
--- a/src/gu/sceGuTexLevelMode.c
+++ b/src/gu/sceGuTexLevelMode.c
@@ -12,6 +12,12 @@
 
 void sceGuTexLevelMode(unsigned int mode, float bias)
 {
+#ifdef GU_DEBUG
+	printf("sceGuTexLevelMode(%08X, %f);\n", mode, bias);
+	assert(gu_init && "GU not initialized");
+	assert((mode == GU_TEXTURE_AUTO || mode == GU_TEXTURE_CONST || mode == GU_TEXTURE_SLOPE) && "Invalid texture level mode");
+#endif
+
 	int offset = (int)truncf(bias * 16.0f);
 
 	// mip map bias?
diff --git a/src/gu/sceGuTexMapMode.c b/src/gu/sceGuTexMapMode.c
index 3f4b5871..227ea550 100644
--- a/src/gu/sceGuTexMapMode.c
+++ b/src/gu/sceGuTexMapMode.c
@@ -10,6 +10,12 @@
 
 void sceGuTexMapMode(int mode, unsigned int lu, unsigned int lv)
 {
+#ifdef GU_DEBUG
+	printf("sceGuTexMapMode(%d, %08X, %08X);\n", mode, lu, lv);
+	assert(gu_init && "GU not initialized");
+	assert((mode == GU_TEXTURE_COORDS || mode == GU_TEXTURE_MATRIX || mode == GU_ENVIRONMENT_MAP) && "Invalid texture map mode");
+#endif
+
 	GuContext *context = &gu_contexts[gu_curr_context];
 
 	context->texture_map_mode = mode & 0x03;
diff --git a/src/gu/sceGuTexMode.c b/src/gu/sceGuTexMode.c
index 8d79e49c..faefe668 100644
--- a/src/gu/sceGuTexMode.c
+++ b/src/gu/sceGuTexMode.c
@@ -10,6 +10,16 @@
 
 void sceGuTexMode(int tpsm, int maxmips, int mc, int swizzle)
 {
+#ifdef GU_DEBUG
+	printf("sceGuTexMode(%d, %d, %d, %d);\n", tpsm, maxmips, mc, swizzle);
+	assert(gu_init && "GU not initialized");
+	assert((tpsm == GU_PSM_5650 || tpsm == GU_PSM_5551 || tpsm == GU_PSM_4444 || 
+		tpsm == GU_PSM_8888 || tpsm == GU_PSM_T4 || tpsm == GU_PSM_T8) && "Invalid texture pixel format");
+	assert(maxmips >= 0 && maxmips <= 7 && "Invalid max mipmaps");
+	assert(mc >= 0 && mc <= 1 && "Invalid multiclut value");
+	assert(swizzle >= 0 && swizzle <= 1 && "Invalid texture swizzle");
+#endif
+
 	GuContext *context = &gu_contexts[gu_curr_context];
 	context->texture_mode = tpsm;
 
diff --git a/src/gu/sceGuTexOffset.c b/src/gu/sceGuTexOffset.c
index 6d75ab4c..357d9181 100644
--- a/src/gu/sceGuTexOffset.c
+++ b/src/gu/sceGuTexOffset.c
@@ -10,6 +10,11 @@
 
 void sceGuTexOffset(float u, float v)
 {
+#ifdef GU_DEBUG
+	printf("sceGuTexOffset(%f, %f);\n", u, v);
+	assert(gu_init && "GU not initialized");
+#endif
+
 	sendCommandf(TEX_OFFSET_U, u);
 	sendCommandf(TEX_OFFSET_V, v);
 }
diff --git a/src/gu/sceGuTexProjMapMode.c b/src/gu/sceGuTexProjMapMode.c
index 7ed0d360..8c11fd3a 100644
--- a/src/gu/sceGuTexProjMapMode.c
+++ b/src/gu/sceGuTexProjMapMode.c
@@ -10,6 +10,12 @@
 
 void sceGuTexProjMapMode(int mode)
 {
+#ifdef GU_DEBUG
+	printf("sceGuTexProjMapMode(%d);\n", mode);
+	assert(gu_init && "GU not initialized");
+	assert((mode == GU_POSITION || mode == GU_UV || mode == GU_NORMALIZED_NORMAL || mode == GU_NORMAL) && "Invalid texture projection map mode");
+#endif
+
 	GuContext *context = &gu_contexts[gu_curr_context];
 
 	context->texture_proj_map_mode = ((mode & 0x03) << 8);
diff --git a/src/gu/sceGuTexScale.c b/src/gu/sceGuTexScale.c
index 032b63a2..f804acf3 100644
--- a/src/gu/sceGuTexScale.c
+++ b/src/gu/sceGuTexScale.c
@@ -10,6 +10,11 @@
 
 void sceGuTexScale(float u, float v)
 {
+#ifdef GU_DEBUG
+	printf("sceGuTexScale(%f, %f);\n", u, v);
+	assert(gu_init && "GU not initialized");
+#endif
+
 	sendCommandf(TEX_SCALE_U, u);
 	sendCommandf(TEX_SCALE_V, v);
 }
diff --git a/src/gu/sceGuTexSlope.c b/src/gu/sceGuTexSlope.c
index d12299c8..51557fe2 100644
--- a/src/gu/sceGuTexSlope.c
+++ b/src/gu/sceGuTexSlope.c
@@ -10,5 +10,10 @@
 
 void sceGuTexSlope(float slope)
 {
+#ifdef GU_DEBUG
+	printf("sceGuTexSlope(%f);\n", slope);
+	assert(gu_init && "GU not initialized");
+#endif
+
 	sendCommandf(TEX_LOD_SLOPE, slope);
 }
diff --git a/src/gu/sceGuTexSync.c b/src/gu/sceGuTexSync.c
index b93d84d0..c211a94f 100644
--- a/src/gu/sceGuTexSync.c
+++ b/src/gu/sceGuTexSync.c
@@ -10,5 +10,10 @@
 
 void sceGuTexSync()
 {
+#ifdef GU_DEBUG
+	printf("sceGuTexSync();\n");
+	assert(gu_init && "GU not initialized");
+#endif
+
 	sendCommandi(TEX_SYNC, 0);
 }
diff --git a/src/gu/sceGuTexWrap.c b/src/gu/sceGuTexWrap.c
index b375b233..f3ec7b26 100644
--- a/src/gu/sceGuTexWrap.c
+++ b/src/gu/sceGuTexWrap.c
@@ -10,5 +10,13 @@
 
 void sceGuTexWrap(int u, int v)
 {
-	sendCommandi(TEX_WRAP, (v << 8) | (u));
+#ifdef GU_DEBUG
+	printf("sceGuTexWrap(%d, %d);\n", u, v);
+	assert(gu_init && "GU not initialized");
+	assert((u == GU_CLAMP || u == GU_REPEAT) && "Invalid U wrap mode");
+	assert((v == GU_CLAMP || v == GU_REPEAT) && "Invalid V wrap mode");
+#endif
+
+	int arg = u | (v << 8);
+	sendCommandi(TEX_WRAP, arg);
 }
diff --git a/src/gu/sceGuViewport.c b/src/gu/sceGuViewport.c
index bb582929..1eb00669 100644
--- a/src/gu/sceGuViewport.c
+++ b/src/gu/sceGuViewport.c
@@ -10,6 +10,15 @@
 
 void sceGuViewport(int cx, int cy, int width, int height)
 {
+#ifdef GU_DEBUG
+	printf("sceGuViewport(%d, %d, %d, %d);\n", cx, cy, width, height);
+	assert(gu_init && "GU not initialized");
+	assert(width > 0 && height > 0 && "Invalid viewport dimensions");
+	assert(width <= 4096 && height <= 4096 && "Viewport dimensions too large");
+	assert(cx >= 0 && cx <= 4095 && "Invalid viewport X coordinate");
+	assert(cy >= 0 && cy <= 4095 && "Invalid viewport Y coordinate");
+#endif
+
 	float sx, sy, tx, ty;
   	sx = (float)(width)  *  0.5f;
 	sy = (float)(height) * -0.5f;