From 8633a0cad1d1e66e8f0c00014589b170f197a844 Mon Sep 17 00:00:00 2001
From: alpine9000 <alex.g.brown@gmail.com>
Date: Thu, 17 Mar 2016 08:28:08 +1100
Subject: [PATCH] Updated calling C example

---
 021.calling_c/Makefile    |  2 +-
 021.calling_c/c_code.c    | 33 +++++++++++++++++----------------
 021.calling_c/calling_c.s |  6 +++---
 021.calling_c/init.s      | 25 +++++++++++++++----------
 4 files changed, 36 insertions(+), 30 deletions(-)

diff --git a/021.calling_c/Makefile b/021.calling_c/Makefile
index eb59ecb..8570207 100644
--- a/021.calling_c/Makefile
+++ b/021.calling_c/Makefile
@@ -1,5 +1,5 @@
 SHRINKLER=0
-INTERLACE=0
+INTERLACE=1
 HAM_MODE=1
 
 EXAMPLE_NAME=calling_c
diff --git a/021.calling_c/c_code.c b/021.calling_c/c_code.c
index 365aaff..d034439 100644
--- a/021.calling_c/c_code.c
+++ b/021.calling_c/c_code.c
@@ -6,27 +6,28 @@ typedef union {
   } words;
 } word_extract_t;
 
+typedef struct {
+  unsigned short pad1;
+  unsigned short lo;
+  unsigned short pad2;
+  unsigned short hi;
+} copper_layout_t
+
+
 void 
-PokeBitplanePointers(unsigned short* copper, unsigned char* bitplanes, unsigned offset, unsigned numBitplanes, unsigned screenWidthBytes)
+PokeBitplanePointers(unsigned short* copper, unsigned char* bitplanes, unsigned short interlace, unsigned short numBitplanes, unsigned short screenWidthBytes)
 {
-  int i;
-  copper += offset;
+  char i;
+  word_extract_t extract;
+  copper_layout_t *ptr = copper;
+
+  bitplanes += interlace ? screenWidthBytes*numBitplanes : 0;
 
   for (i = 0; i < numBitplanes; i++) {
-    word_extract_t extract;
     extract.ptr = bitplanes;
-    *(copper+1) = extract.words.lo;
-    *(copper+3) = extract.words.hi;
+    ptr->lo = extract.words.lo;
+    ptr->hi = extract.words.hi;
     bitplanes += screenWidthBytes;
-    copper += 4;
+    ptr++;
   } 
 }
-
-static unsigned short _copperData;
-static unsigned char _bitplaneData;
-
-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 d9a50c2..70c9fdb 100644
--- a/021.calling_c/calling_c.s
+++ b/021.calling_c/calling_c.s
@@ -1,7 +1,7 @@
 	include "includes.i"
 
 	xref	InstallColorPalette
-	;;xref	PokeBitplanePointers
+	xref	PokeBitplanePointers
 	xref	copperList
 	xref 	copperListAlternate
 	xref	bitplanes
@@ -27,12 +27,12 @@ Entry:
 	bra	.mainLoop
 
 ;===========================================================
-	if 0
+	if 1
 PokeBitplanePointers:
 	; d0 = frame offset in bytes;
 	; a0 = BPLP copper list address 
 	movem.l	d0-a6,-(sp)
-	move.l	bitplanes,a1
+	lea	bitplanes,a1
 	add.l	d0,a1 ; Offset for odd/even frames
 	moveq	#SCREEN_BIT_DEPTH-1,d0
 .bitplaneloop:
diff --git a/021.calling_c/init.s b/021.calling_c/init.s
index d697881..b1af005 100644
--- a/021.calling_c/init.s
+++ b/021.calling_c/init.s
@@ -12,22 +12,27 @@ Init:
 	;; set up default palette
 	jsr	InstallColorPalette
 
+	;; Make a call to a C function with the following prototype:
+	;; void PokeBitplanePointers(unsigned short* copper, unsigned char* bitplanes, unsigned short interlace, unsigned short numBitplanes, unsigned short screenWidthBytes)
+	
 	if INTERLACE == 1
 	;; poke the bitplane pointers for the two copper lists.
-	move.l	#SCREEN_WIDTH_BYTES*SCREEN_BIT_DEPTH,d0
-	lea 	copperListAlternate,a0
-	jsr	PokeBitplanePointers
+	move.l 	#SCREEN_WIDTH_BYTES,-(sp) ; arguments are pushed onto the stack...
+	move.l 	#SCREEN_BIT_DEPTH,-(sp)	  ; in reverse order. 16 bit variables are passed as 32 bits.
+	move.l	#1,-(sp)		  ; interlace line.
+	pea	bitplanes                 ; make sure you push the address...
+	pea	copperListAlternate       ; 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.
 	endif
 
-	;; 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
+	move.l 	#SCREEN_BIT_DEPTH,-(sp)	  ; in reverse order.
+	move.l	#0,-(sp)		  ; normal line.
 	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
+	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)