diff --git a/021.calling_c/c_code.c b/021.calling_c/c_code.c
index bbbae09..79657c0 100644
--- a/021.calling_c/c_code.c
+++ b/021.calling_c/c_code.c
@@ -14,7 +14,8 @@ PokeBitplanePointers(unsigned short* copper, unsigned char* bitplanes, unsigned
 
 static unsigned short _copperData;
 static unsigned char _bitplaneData;
-static void
+
+void
 TestCall()
 {
   PokeBitplanePointers(&_copperData, &_bitplaneData, 3, 4, 5);
diff --git a/021.calling_c/calling_c.s b/021.calling_c/calling_c.s
index 772ecec..d9a50c2 100644
--- a/021.calling_c/calling_c.s
+++ b/021.calling_c/calling_c.s
@@ -28,7 +28,9 @@ Entry:
 
 ;===========================================================
 	if 0
-PokeBitplanePointers: 		; d0 = frame offset in bytes, a0 = BPLP copper list address
+PokeBitplanePointers:
+	; d0 = frame offset in bytes;
+	; a0 = BPLP copper list address 
 	movem.l	d0-a6,-(sp)
 	move.l	bitplanes,a1
 	add.l	d0,a1 ; Offset for odd/even frames
diff --git a/021.calling_c/init.s b/021.calling_c/init.s
index b54d055..d697881 100644
--- a/021.calling_c/init.s
+++ b/021.calling_c/init.s
@@ -19,14 +19,15 @@ Init:
 	jsr	PokeBitplanePointers
 	endif
 
-	;; 	void PokeBitplanePointers(unsigned short* copper, unsigned char* bitplanes, unsigned offset, unsigned numBitplanes, unsigned screenWidthBytes)
-	move.l 	#SCREEN_WIDTH_BYTES,-(sp)
-	move.l 	#SCREEN_BIT_DEPTH,-(sp)
-	move.l	#0,-(sp)
-	pea	bitplanes
-	pea	copperList
-	jsr	_PokeBitplanePointers	
-	add.l   #20,sp
+	;; Make a call to a C function with the following prototype:
+	;; void PokeBitplanePointers(unsigned short* copper, unsigned char* bitplanes, unsigned offset, unsigned numBitplanes, unsigned screenWidthBytes)
+	move.l 	#SCREEN_WIDTH_BYTES,-(sp) ; arguments are pushed onto the stack...
+	move.l 	#SCREEN_BIT_DEPTH,-(sp)	  ; in reverse order
+	move.l	#0,-(sp)		  ; offset == 0
+	pea	bitplanes                 ; make sure you push the address...
+	pea	copperList                ; of variables, not the value
+	jsr	_PokeBitplanePointers	  ; C adds an _ to all global symbols
+	add.l   #20,sp          	  ; Need to pop the arguments from the stack
 	
 	;; set up playfield
 	move.w  #(RASTER_Y_START<<8)|RASTER_X_START,DIWSTRT(a6)
diff --git a/shared/base.mk b/shared/base.mk
index 3a4398d..972a1d3 100644
--- a/shared/base.mk
+++ b/shared/base.mk
@@ -93,6 +93,7 @@ out/%.o: %.s
 out/%.o: %.c
 	vc -O3 -c $< -o $@
 	-@vc -O3 -S $< -o out/$*.s > /dev/null 2> /dev/null
+	-@vc -O0 -S $< -o out/$*-noopt.s > /dev/null 2> /dev/null
 
 out/main.bin: out/main.o $(OBJS)
 	@#-T ../link.script