several features are now optional, added legacy BASIC memory model

c64/aliases/,aliases_hardware.s

@@ -10,6 +10,8 @@
 
 	// VIC-II registers
 
+	.label VIC_BASE     = $D000  // base address of the chip
+
 	.label VIC_SP0X     = $D000
 	.label VIC_SP0Y     = $D001
 	.label VIC_SP1X     = $D002
@@ -62,6 +64,8 @@
 	
 	// SID registers
 
+	.label SID_BASE     = $D400  // base address of the chip
+
 	.label SID_FRELO1   = $D400
 	.label SID_FREHI1   = $D401
 	.label SID_PWLO1    = $D402
@@ -97,6 +101,8 @@
 
 	// CIA #1 registers
 
+	.label CIA1_BASE    = $DC00  // base address of the chip
+
 	.label CIA1_PRA     = $DC00
 	.label CIA1_PRB     = $DC01
 	.label CIA1_DDRA    = $DC02
@@ -119,6 +125,8 @@
 
 	// CIA #2 registers
 
+	.label CIA2_BASE    = $DD00  // base address of the chip
+
 	.label CIA2_PRA     = $DD00  // VIC bank switching and IEC port
 	.label CIA2_PRB     = $DD01
 	.label CIA2_DDRA    = $DD02