1 files changed, 91 insertions, 0 deletions
diff --git a/memory.s b/memory.s
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+|| -*- gas -*-
+
+|| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
+||  _ __ ___   ___ _ __ ___   ___  _ __ _   _   |||||||||||||||||||||||||||
+|| | '_ ` _ \ / _ \ '_ ` _ \ / _ \| '__| | | |  \\\\\\\\\\\\\\\\\\\\\\\\\\\
+|| | | | | | |  __/ | | | | | (_) | |  | |_| |  |||||||||||||||||||||||||||
+|| |_| |_| |_|\___|_| |_| |_|\___/|_|   \__, |  ///////////////////////////
+|| of the virtual type                  |___/   |||||||||||||||||||||||||||
+|| =============================================JJJJJJJJJJJJJJJJJJJJJJJJJJJ
+
+	|| Take a virtual address in d1 and dereference it.  Returns the
+	|| host address in a0.  Destroys a0, d0.
+deref:	| 76 cycles + 18 cycles for bsr
+	| 20 bytes to inline, saves 34 cycles per call
+	move.w	d1,d0
+	andi.w	#0x3FFF,d0
+	movea.w	d0,a0
+	move.w	d1,d0
+	andi.w	#0xC000,d0	| Can cut this out by pre-masking the table.
+	rol.w	#4,d0
+	adda.l	deref_table(pc,d0.w),a0	| TODO gas doesn't like this
+	rts
+
+.even
+.bss
+deref_table:
+mem_page_0:	.long	0		| bank 0 / 0x0000
+mem_page_1:	.long	0		| bank 1 / 0x4000
+mem_page_2:	.long	0		| bank 2 / 0x8000
+mem_page_3:	.long	0		| bank 3 / 0xc000
+
+.xdef	mem_page_0
+.xdef	mem_page_1
+.xdef	mem_page_2
+.xdef	mem_page_3
+
+mem_page_loc_0:	.byte	0
+mem_page_loc_1:	.byte	0
+mem_page_loc_2:	.byte	0
+mem_page_loc_3:	.byte	0
+
+.xdef	mem_page_loc_0
+.xdef	mem_page_loc_1
+.xdef	mem_page_loc_2
+.xdef	mem_page_loc_3
+
+pages:	.long	0
+
+.xdef pages
+
+.text
+
+	|| Take a physical address in a0 and turn it into a virtual
+	|| address in d0
+	|| Destroys d0, a1
+| XXX AFAICS, a1 is currently a scratch address register, so you can load deref_table in it, and then save some space:
+| But you may wish to use it for other purposes in the future, so you needn't integrate that immediately.
+
+	|| Guessing this is 300 cycles.
+underef:
+	move.l	d2,-(a7)
+	lea	deref_table(pc),a1
+	move.l	a0,d0
+	clr.w	d2
+	sub.l	(a1)+,d0
+	bmi.s	underef_not0
+	cmpi.l	#0x4000,d0
+	bmi.s	underef_thatsit
+underef_not0:
+	move.l	a0,d0
+	move.w	#0x4000,d2
+	sub.l	(a1)+,d0
+	bmi.s	underef_not1
+	cmpi.l	#0x4000,d0
+	bmi.s	underef_thatsit
+underef_not1:
+	move.l	a0,d0
+	move.w	#0x8000,d2
+	sub.l	(a1)+,d0
+	bmi.s	underef_not2
+	cmpi.l	#0x4000,d0
+	bmi.s	underef_thatsit
+underef_not2:
+	move.w	#0xc000,d2
+	suba.l	(a1)+,a0
+	|| if that fails too, well shit man!
+	moveq	#0,d0
+underef_thatsit:
+	add.w	d2,d0
+	move.l	(a7)+,d2
+	rts