From 104ed3f6f12e80e38df5c939ba9817068cefaa54 Mon Sep 17 00:00:00 2001
From: alpine9000 <alex.g.brown@gmail.com>
Date: Wed, 23 Mar 2016 13:59:12 +1100
Subject: [PATCH] Cleaning up

---
 023.slideshow/blitter.s | 68 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 68 insertions(+)
 create mode 100644 023.slideshow/blitter.s

diff --git a/023.slideshow/blitter.s b/023.slideshow/blitter.s
new file mode 100644
index 0000000..d618026
--- /dev/null
+++ b/023.slideshow/blitter.s
@@ -0,0 +1,68 @@
+	include "exec/types.i"
+	include "hardware/custom.i"
+	include "hardware/dmabits.i"
+	include "hardware/blit.i"
+	include "../include/registers.i"
+
+	xdef	ClearMemory
+	xdef	WaitBlitter
+
+WaitBlitter:
+	        btst.b  #DMAB_BLTDONE-8,DMACONR(a1)
+.wait:
+	        btst.b  #DMAB_BLTDONE-8,DMACONR(a1)
+	        bne     .wait
+	        rts
+	
+	;;
+	;;    This routine uses a side effect in the blitter.  When each
+	;;    of the blits is finished, the pointer in the blitter is pointing
+	;;    to the next word to be blitted.
+	;;
+	;;    When this routine returns, the last blit is started and might
+	;;    not be finished, so be sure to call waitblit above before
+	;;    assuming the data is clear.
+	;;
+	;;    a0 = pointer to first word to clear
+	;;    d0 = number of bytes to clear (must be even)
+	;;
+
+ClearMemory:
+	        move.l  CUSTOM,a1     ; Get pointer to chip registers
+	        bsr     WaitBlitter   ; Make sure previous blit is done
+	        move.l  a0,BLTDPT(a1) ; Set up the D pointer to the region to clear
+	        clr.w   BLTDMOD(a1)   ; Clear the D modulo (don't skip no bytes)
+	        asr.l   #1,d0	      ; Get number of words from number of bytes
+	        clr.w   BLTCON1(a1)   ; No special modes
+	        move.w  #DEST,BLTCON0(a1) ; only enable destination
+	;;
+	;;    First we deal with the smaller blits
+	;;
+	        moveq   #$3f,d1	; Mask out mod 64 words
+	        and.w   d0,d1
+	        beq     dorest	; none?  good, do one blit
+	        sub.l   d1,d0	; otherwise remove remainder
+	        or.l    #$40,d1	; set the height to 1, width to n
+	        move.w  d1,BLTSIZE(a1) ; trigger the blit
+	;;
+	;;    Here we do the rest of the words, as chunks of 128k
+	;;
+dorest:
+	        move.w  #$ffc0,d1 	; look at some more upper bits
+	        and.w   d0,d1	  	; extract 10 more bits
+	        beq     dorest2	  	; any to do?
+	        sub.l   d1,d0	  	; pull of the ones we're doing here
+	        bsr     WaitBlitter 	; wait for prev blit to complete
+	        move.w  d0,BLTSIZE(a1) 	; do another blit
+dorest2:
+	        swap    d0	; more?
+	        beq     done	; nope.
+	        clr.w   d1	; do a 1024x64 word blit (128K)
+keepon:
+	        bsr     WaitBlitter 	; finish up this blit
+	        move.w  d1,BLTSIZE(a1) 	; and again, blit
+	        subq.w  #1,d0	       	; still more?
+	        bne     keepon	       	; keep on going.
+done:
+	        rts			; finished.  Blit still in progress.
+	        end	
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