added ZP shadowing for monitor and Z80 CPU emulator

src/aliases/,aliases_ram_lowmem.s

@@ -153,7 +153,7 @@
 	!addr KEYTAB    = $F5  ; $F5-$F6  pointer to keyboard lookup table
 	!addr RIBUF     = $F7  ; $F7-$F8  -- WIP -- RS-232 receive buffer pointer
 	!addr ROBUF     = $F9  ; $F9-$FA  -- WIP -- RS-232 send buffer pointer
-	;                 $FB     $FB-$FE  -- UNUSED --          free for user software
+	;                 $FB    $FB-$FE  -- UNUSED --          free for user software
 	!addr BASZPT    = $FF  ;          -- NOT IMPLEMENTED --
 
 	;

src/aliases/,aliases_ram_over64K_m65.s

@@ -20,5 +20,12 @@
 	;                (2KB) - color RAM mirror, not useable
 	; $20000-$2FFFF (64KB) - ROM, the essential part
 	; $30000-$4FFFF (64KB) - ROM, additions
-	; $50000-$57FFF (32KB) - reserved for graphics screen
+	; $50000-$57F71 (32KB) - reserved for graphics screen
+	; $57F72-$57FFF        - shadow location for BASIC zeropage
+
+!set MEMCONF_SHADOW_BZP_0 = $72
+!set MEMCONF_SHADOW_BZP_1 = $7F
+!set MEMCONF_SHADOW_BZP_2 = $05
+!set MEMCONF_SHADOW_BZP_3 = $00
+
 	; $58000-...           - extended BASIC variables, RAM disk, etc.

src/kernal/board_m65/4000.mega65_vectable_kernal_1.s

@@ -26,6 +26,7 @@
 	!addr VK1__M65_CLRSCR                = $4000 + 2 * 12
 	!addr VK1__M65_CLRWIN                = $4000 + 2 * 13
 	!addr VK1__m65_screen_upd_txtrow_off = $4000 + 2 * 14
+	!addr VK1__m65_shadow_BZP            = $4000 + 2 * 15
 
 } else {
 
@@ -60,4 +61,5 @@
 	!word M65_CLRSCR	
 	!word M65_CLRWIN
 	!word m65_screen_upd_txtrow_off
+	!word m65_shadow_BZP
 }

src/kernal/board_m65/mega65_monitor.s

@@ -4,7 +4,8 @@
 
 MONITOR:
 
+	jsr m65_shadow_BZP
 	jsr map_MON_1
 	jmp ($4000)
 
-	; Monitor knows, that it should exit via map_NORMAL
+	; Monitor knows, that it should exit via m65_shadow_BZP

src/kernal/board_m65/mega65_shadow_bzp.s

@@ -0,0 +1,80 @@
+;; #LAYOUT# M65 KERNAL_0 #TAKE
+;; #LAYOUT# M65 KERNAL_1 #TAKE
+;; #LAYOUT# *   *        #IGNORE
+
+; Exchanges BASIC part of the zero page with it's shadow location; tries to destroy as little memory as possible
+
+
+m65_shadow_BZP:
+
+!ifdef SEGMENT_M65_KERNAL_0 {
+
+	jsr map_KERNAL_1
+	jsr (VK1__m65_shadow_BZP)
+	jmp map_NORMAL
+
+} else {
+
+
+	; Preserve CPU status and registers
+
+	php
+	phz
+	pha
+	phx
+
+	; We need a 4-byte pointer on the zero page; let's use the ones starting from FNLEN
+
+	ldx #$03
+@1:
+	lda FNLEN,x
+	pha
+	dex
+	bpl @1
+
+	; Store the address of the ZP shadow location
+
+	lda #MEMCONF_SHADOW_BZP_0
+	sta FNLEN+0
+	lda #MEMCONF_SHADOW_BZP_1
+	sta FNLEN+1
+	lda #MEMCONF_SHADOW_BZP_2
+	sta FNLEN+2
+	lda #MEMCONF_SHADOW_BZP_3
+	sta FNLEN+3
+
+	; Exchange the ZP content
+
+	ldz #$00
+	ldx #$00
+@2:
+	lda [FNLEN],z
+	pha
+	lda $02,x
+	sta [FNLEN],z
+	pla
+	sta $02,x
+	inz
+	inx
+	cpx #$8E
+	bne @2
+
+	; Restore FNLEN and further bytes
+
+	ldx #$00
+@3:
+	pla
+	sta FNLEN,x
+	inx
+	cpx #$04
+	bne @3
+
+	; Restore registers and quit
+
+	plx
+	pla
+	plz
+	plp
+
+	rts
+}

src/mon_m65/,imports_monitor.s

@@ -9,6 +9,7 @@
 
 ;; #ALIAS# map_NORMAL        = KERNAL_0.map_NORMAL
 ;; #ALIAS# map_MON_1         = KERNAL_0.map_MON_1
+;; #ALIAS# m65_shadow_BZP    = KERNAL_0.m65_shadow_BZP
 
 ;; #ALIAS# CHRIN             = KERNAL_0.proxy_M1_CHRIN
 ;; #ALIAS# CHROUT            = KERNAL_0.proxy_M1_CHROUT

src/mon_m65/bsmon.s

@@ -60,8 +60,8 @@
 
 !addr MODE_80     = $d7        ; 80 column / 40 volumn flag ; XXX add routine to detect this
 
-!addr Disk_Status     = $40A       ; BCD value of status
+!addr Disk_Status = $40A       ; BCD value of status
-!addr Disk_Msg        = $410       ; 40 bytes, disk status as text message ; XXX get rid of this buffer
+!addr Disk_Msg    = $410       ; 40 bytes, disk status as text message ; XXX get rid of this buffer
 
 
 ; *******
@@ -109,8 +109,8 @@ Mon_Call
 
 ;        set default PC to monitor exit point
 
-         LDA  #<map_NORMAL
+         LDA  #<m65_shadow_BZP
-         LDX  #>map_NORMAL
+         LDX  #>m65_shadow_BZP
          STA  PCL
          STA  MON_XVEC
          STX  PCH