preparation for using DMAgic in the screen editor

src/kernal/board_m65/mega65_dmagic.s

@@ -0,0 +1,63 @@
+// #LAYOUT# M65 KERNAL_0 #TAKE
+// #LAYOUT# *   *        #IGNORE
+
+// Helper routines for DMAgic usage
+
+// See:
+// - https://c65gs.blogspot.com/2019/03/auto-detecting-required-revision-of.html
+// - https://c65gs.blogspot.com/2018/01/improving-dmagic-controller-interface.html
+
+
+// XXX: finish the implementation, use in screen editor
+
+
+m65_dmagic_oper_copy:
+
+	// To configure parameters, use:
+	// - M65_DMAJOB_SIZE_*
+	// - M65_DMAJOB_SRC_*
+	// - M65_DMAJOB_DST_*	
+
+	lda #$00
+	sta M65_DMAGIC_LIST+6              // operation: copy
+
+	jmp_8 m65_dmagic_common
+
+m65_dmagic_oper_fill:
+
+	// XXX provide implementation
+
+	// FALLTROUGH
+
+m65_dmagic_common:
+
+	lda #$0A
+	sta M65_DMAGIC_LIST+0              // <- $0A = use F018A list format (it is shorter by 1 byte)
+	lda #$80
+	sta M65_DMAGIC_LIST+1              // <- $80 = next byte is highest 8 bits of source address
+	inc_a
+	sta M65_DMAGIC_LIST+3              // <- $80 = next byte is highest 8 bits of destination address
+
+	lda #$00
+	sta M65_DMAGIC_LIST+5              // <- end of options
+
+	sta M65_DMAGIC_LIST+15             // <- set modulo to 0
+	sta M65_DMAGIC_LIST+16
+
+	// FALLTROUGH
+
+m65_dmagic_launch:
+
+	// Launch the DMA list
+
+	lda #$00
+	sta DMA_ADDRBANK                   // $D702
+	sta DMA_ADDRMB                     // $D704
+
+	lda #>M65_DMAGIC_LIST
+	sta DMA_ADDRMSB                    // $D701
+
+	lda #<M65_DMAGIC_LIST
+	sta DMA_ETRIG                      // $D705
+
+	rts