diff --git a/Makefile b/Makefile
index d5a522871..b4882cc31 100644
--- a/Makefile
+++ b/Makefile
@@ -1,4 +1,4 @@
-all mostlyclean clean:
+all mostlyclean clean install:
 	@$(MAKE) -C src    --no-print-directory $@
 	@$(MAKE) -C libsrc --no-print-directory $@
 
@@ -14,6 +14,6 @@ lib:
 %:
 	@$(MAKE) -C libsrc --no-print-directory $@
 
-.PHONY: all mostlyclean clean avail unavail bin lib
+.PHONY: all mostlyclean clean install avail unavail bin lib
 
 .SUFFIXES:
diff --git a/asminc/atari.inc b/asminc/atari.inc
index da926af81..7b647fd0a 100644
--- a/asminc/atari.inc
+++ b/asminc/atari.inc
@@ -318,7 +318,7 @@ APPMHI  = $0E           ;APPLICATIONS MEMORY HI LIMIT
 
 INTZBS  = $10           ;INTERRUPT HANDLER
 
-POKMSK  = $10           ;SYSTEM MASK FOR POKEY IRQ ENABLE
+POKMSK  = $10           ;SYSTEM MASK FOR POKEY IRQ ENABLE (shadow of IRQEN)
 BRKKEY  = $11           ;BREAK KEY FLAG
 RTCLOK  = $12           ;REAL TIME CLOCK (IN 16 MSEC UNITS>
 BUFADR  = $15           ;INDIRECT BUFFER ADDRESS REGISTER
diff --git a/cfg/apple2-asm.cfg b/cfg/apple2-asm.cfg
index e70ed4484..1e187764c 100644
--- a/cfg/apple2-asm.cfg
+++ b/cfg/apple2-asm.cfg
@@ -8,13 +8,15 @@ SYMBOLS {
     __LOADSIZE__: type = weak, value = __BSS_RUN__ - __CODE_RUN__;
 }
 MEMORY {
+    ZP:                start = $0080, size = $001A,      define = yes;
     HEADER: file = %O, start = $0000, size = $0004;
     RAM:    file = %O, start = %S,    size = $C000 - %S;
 }
 SEGMENTS {
-    EXEHDR: load = HEADER, type = ro,  optional = yes;
-    CODE:   load = RAM,    type = rw,  optional = yes, define = yes;
-    RODATA: load = RAM,    type = ro,  optional = yes;
-    DATA:   load = RAM,    type = rw,  optional = yes;
-    BSS:    load = RAM,    type = bss, optional = yes, define = yes;
+    ZEROPAGE: load = ZP,     type = zp,  optional = yes;
+    EXEHDR:   load = HEADER, type = ro,  optional = yes;
+    CODE:     load = RAM,    type = rw,  optional = yes, define = yes;
+    RODATA:   load = RAM,    type = ro,  optional = yes;
+    DATA:     load = RAM,    type = rw,  optional = yes;
+    BSS:      load = RAM,    type = bss, optional = yes, define = yes;
 }
diff --git a/cfg/atari-asm.cfg b/cfg/atari-asm.cfg
index 4e87a8884..4ff7c3173 100644
--- a/cfg/atari-asm.cfg
+++ b/cfg/atari-asm.cfg
@@ -24,6 +24,7 @@ SEGMENTS {
     RODATA:    load = RAM,        type = ro                 optional = yes;
     DATA:      load = RAM,        type = rw                 optional = yes;
     BSS:       load = RAM,        type = bss, define = yes, optional = yes;
-    ZEROPAGE:  load = ZP,         type = zp;
+    ZEROPAGE:  load = ZP,         type = zp,                optional = yes;
+    EXTZP:     load = ZP,         type = zp,                optional = yes; # to enable modules to be able to link to C and assembler programs
     AUTOSTRT:  load = TRAILER,    type = ro,                optional = yes;
 }
diff --git a/cfg/atari-cart.cfg b/cfg/atari-cart.cfg
index 10674dc49..db9486a9f 100644
--- a/cfg/atari-cart.cfg
+++ b/cfg/atari-cart.cfg
@@ -24,7 +24,7 @@ SEGMENTS {
     DATA:      load = ROM, run = RAM, type = rw,  define = yes, optional = yes;
     BSS:       load = RAM,            type = bss, define = yes, optional = yes;
     CARTHDR:   load = CARTID,         type = ro;
-    ZEROPAGE:  load = ZP,             type = zp;
+    ZEROPAGE:  load = ZP,             type = zp,                optional = yes;
     EXTZP:     load = ZP,             type = zp,                optional = yes;
 }
 FEATURES {
diff --git a/cfg/c64-asm.cfg b/cfg/c64-asm.cfg
index 0924cdb56..1ab80be8e 100644
--- a/cfg/c64-asm.cfg
+++ b/cfg/c64-asm.cfg
@@ -5,6 +5,7 @@ SYMBOLS {
     __LOADADDR__: type = import;
 }
 MEMORY {
+    ZP:       file = "", start = $0002,  size = $001A,      define = yes;
     LOADADDR: file = %O, start = %S - 2, size = $0002;
     RAM:      file = %O, start = %S,     size = $D000 - %S;
 }
@@ -15,4 +16,5 @@ SEGMENTS {
     RODATA:   load = RAM,      type = ro,  optional = yes;
     DATA:     load = RAM,      type = rw,  optional = yes;
     BSS:      load = RAM,      type = bss, optional = yes;
+    ZEROPAGE: load = ZP,       type = zp,  optional = yes;
 }
diff --git a/include/atari.h b/include/atari.h
index ff23526ee..82cd07330 100644
--- a/include/atari.h
+++ b/include/atari.h
@@ -169,9 +169,16 @@ extern char *_getdefdev(void);          /* get default floppy device */
 
 /* global variables */
 extern unsigned char _dos_type;         /* the DOS flavour */
+#ifndef __ATARIXL__
 extern void atr130_emd[];
 extern void atrstd_joy[];               /* referred to by joy_static_stddrv[] */
 extern void atrmj8_joy[];
+extern void atrjoy_mou[];
+extern void atrst_mou[];                /* referred to by mouse_static_stddrv[] */
+extern void atrami_mou[];
+extern void atrtrk_mou[];
+extern void atrtt_mou[];
+extern void atrrdev_ser[];
 extern void atr3_tgi[];
 extern void atr4_tgi[];
 extern void atr5_tgi[];
@@ -187,6 +194,32 @@ extern void atr11_tgi[];
 extern void atr14_tgi[];
 extern void atr15_tgi[];
 extern void atr15p2_tgi[];
+#else
+extern void atrx130_emd[];
+extern void atrxstd_joy[];              /* referred to by joy_static_stddrv[] */
+extern void atrxmj8_joy[];
+extern void atrxjoy_mou[];
+extern void atrxst_mou[];               /* referred to by mouse_static_stddrv[] */
+extern void atrxami_mou[];
+extern void atrxtrk_mou[];
+extern void atrxtt_mou[];
+extern void atrxrdev_ser[];
+extern void atrx3_tgi[];
+extern void atrx4_tgi[];
+extern void atrx5_tgi[];
+extern void atrx6_tgi[];
+extern void atrx7_tgi[];
+extern void atrx8_tgi[];                /* referred to by tgi_static_stddrv[] */
+extern void atrx8p2_tgi[];
+extern void atrx9_tgi[];
+extern void atrx9p2_tgi[];
+extern void atrx10_tgi[];
+extern void atrx10p2_tgi[];
+extern void atrx11_tgi[];
+extern void atrx14_tgi[];
+extern void atrx15_tgi[];
+extern void atrx15p2_tgi[];
+#endif
 
 /* provide old names for backwards compatibility */
 #ifdef ATARI_COMPAT_PRE_2_11
diff --git a/libsrc/Makefile b/libsrc/Makefile
index fb716067b..cbc778f11 100644
--- a/libsrc/Makefile
+++ b/libsrc/Makefile
@@ -50,10 +50,18 @@ endif
 
 .SUFFIXES:
 
-.PHONY: all lib $(TARGETS) mostlyclean clean
+.PHONY: all lib $(TARGETS) mostlyclean clean install
 
 ifndef TARGET
 
+datadir = $(prefix)/share/cc65
+
+INSTALLDIRS = ../asminc ../cfg ../include \
+              $(filter-out $(wildcard ../include/*.*),$(wildcard ../include/*)) \
+              ../lib ../targetutil $(addprefix ../,$(DRVTYPES))
+
+INSTALL = install
+
 all lib: $(TARGETS)
 
 $(TARGETS):
@@ -65,6 +73,21 @@ mostlyclean:
 clean:
 	$(call RMDIR,../wrk ../lib ../targetutil $(addprefix ../,$(DRVTYPES)))
 
+install:
+	$(foreach dir,$(INSTALLDIRS),$(INSTALL_recipe))
+
+##########
+
+define INSTALL_recipe
+
+$(if $(prefix),,$(error variable `prefix' must be set))
+$(INSTALL) -d $(subst ..,$(DESTDIR)$(datadir),$(dir))
+$(INSTALL) -m644 $(dir)/* $(subst ..,$(DESTDIR)$(datadir),$(dir))
+
+endef
+
+##########
+
 else # TARGET
 
 CA65FLAGS =
diff --git a/libsrc/apple2/crt0.s b/libsrc/apple2/crt0.s
index 27c44f016..a140a7249 100644
--- a/libsrc/apple2/crt0.s
+++ b/libsrc/apple2/crt0.s
@@ -107,7 +107,7 @@ exit:   ldx     #$02
         txs                     ; Re-init stack pointer
 
         ; We're done
-        jmp     (done)
+        jmp     done
 
         .segment        "INIT"
 
@@ -148,8 +148,8 @@ init:   ldx     #zpspace-1
         ; No BASIC.SYSTEM so quit to ProDOS dispatcher instead
         lda     #<quit
         ldx     #>quit
-        sta     done
-        stx     done+1
+        sta     done+1
+        stx     done+2
         
         ; No BASIC.SYSTEM so use addr of ProDOS system global page
         lda     #<$BF00
@@ -202,8 +202,8 @@ q_param:.byte   $04             ; param_count
 
         .data
 
-        ; Location to jump to when we're done
-done:   .addr   DOSWARM
+        ; Final jump when we're done
+done:   jmp     DOSWARM         ; Potentially patched at runtime
 
         .segment        "ZPSAVE"
 
diff --git a/libsrc/apple2/exec.s b/libsrc/apple2/exec.s
index 914e10c50..c486306bb 100644
--- a/libsrc/apple2/exec.s
+++ b/libsrc/apple2/exec.s
@@ -161,8 +161,8 @@ setbuf: lda     #$00            ; Low byte
         ; Call loader stub after C libary shutdown
         lda     #<target
         ldx     #>target
-        sta     done
-        stx     done+1
+        sta     done+1
+        stx     done+2
 
         ; Initiate C libary shutdown
         jmp     _exit
diff --git a/libsrc/apple2/reboot.s b/libsrc/apple2/reboot.s
index 89c34bdf0..8ee1ba067 100644
--- a/libsrc/apple2/reboot.s
+++ b/libsrc/apple2/reboot.s
@@ -16,6 +16,6 @@ initreboot:
         ; Quit to PWRUP
         lda     #<$FAA6
         ldx     #>$FAA6
-        sta     done
-        stx     done+1
+        sta     done+1
+        stx     done+2
         rts
diff --git a/libsrc/atari/joy_stat_stddrv.s b/libsrc/atari/joy_stat_stddrv.s
index cbaf344d0..4528aa20d 100644
--- a/libsrc/atari/joy_stat_stddrv.s
+++ b/libsrc/atari/joy_stat_stddrv.s
@@ -7,8 +7,16 @@
 ;
 
         .export _joy_static_stddrv
+        .ifdef  __ATARIXL__
+        .import _atrxstd_joy
+        .else
         .import _atrstd_joy
+        .endif
 
 .rodata
 
+        .ifdef  __ATARIXL__
+_joy_static_stddrv := _atrxstd_joy
+        .else
 _joy_static_stddrv := _atrstd_joy
+        .endif
diff --git a/libsrc/atari/joy_stddrv.s b/libsrc/atari/joy_stddrv.s
index f3ab74e7b..e82dadb73 100644
--- a/libsrc/atari/joy_stddrv.s
+++ b/libsrc/atari/joy_stddrv.s
@@ -10,4 +10,9 @@
 
 .rodata
 
-_joy_stddrv:    .asciiz "atrstd.joy"
+_joy_stddrv:
+        .ifdef  __ATARIXL__
+                .asciiz "atrxstd.joy"
+        .else
+                .asciiz "atrstd.joy"
+        .endif
diff --git a/libsrc/atari/mou/atrst.s b/libsrc/atari/mou/atrst.s
index 116cecee2..773e171e1 100644
--- a/libsrc/atari/mou/atrst.s
+++ b/libsrc/atari/mou/atrst.s
@@ -446,6 +446,14 @@ IOCTL:  lda     #<MOUSE_ERR_INV_IOCTL     ; We don't support ioclts for now
 
 IRQ:
 
+; Turn mouse polling IRQ back on in case it disabled itself due to CRITIC
+; flag being set.
+
+        lda     POKMSK
+        ora     #%00000001              ; timer 1 enable
+        sta     POKMSK
+        sta     IRQEN
+
 ; Check for a pressed button and place the result into Buttons
 
         ldx     #0
@@ -514,7 +522,12 @@ IRQ:
 ; T1Han: Local IRQ routine to poll mouse
 ;
 
-T1Han:  tya
+T1Han:  lda     CRITIC                  ; if CRITIC flag is set, disable the
+        bne     disable_me              ; high frequency polling IRQ, in order
+                                        ; not to interfere with SIO I/O (e.g.
+                                        ; floppy access)
+
+        tya
         pha
         txa
         pha
@@ -695,3 +708,22 @@ mmexit: sty     oldval
         pla
         rti
 .endif
+
+
+; Disable the interrupt source which caused us to be called.
+; The interrupt will be enabled again by the "IRQ" routine.
+; The "IRQ" routine, despite its name, is called from the
+; vertical blank NMI interrupt *only* if the CRITIC flag has
+; been cleared.
+
+disable_me:
+        lda     POKMSK
+        and     #%11111110              ; timer 1 disable
+        sta     IRQEN
+        sta     POKMSK
+.ifdef  __ATARIXL__
+        rts
+.else
+        pla
+        rti
+.endif
diff --git a/libsrc/atari/tgi_stat_stddrv.s b/libsrc/atari/tgi_stat_stddrv.s
index 5f1be70f8..dc3b7cc71 100644
--- a/libsrc/atari/tgi_stat_stddrv.s
+++ b/libsrc/atari/tgi_stat_stddrv.s
@@ -7,8 +7,16 @@
 ;
 
         .export _tgi_static_stddrv
+        .ifdef  __ATARIXL__
+        .import _atrx8_tgi
+        .else
         .import _atr8_tgi
+        .endif
 
 .rodata
 
+        .ifdef  __ATARIXL__
+_tgi_static_stddrv := _atrx8_tgi
+        .else
 _tgi_static_stddrv := _atr8_tgi
+        .endif
diff --git a/libsrc/atari/tgi_stddrv.s b/libsrc/atari/tgi_stddrv.s
index bec030511..e2f68a50e 100644
--- a/libsrc/atari/tgi_stddrv.s
+++ b/libsrc/atari/tgi_stddrv.s
@@ -10,4 +10,9 @@
 
 .rodata
 
-_tgi_stddrv:    .asciiz "atr8.tgi"
+_tgi_stddrv:
+        .ifdef  __ATARIXL__
+                .asciiz "atrx8.tgi"
+        .else
+                .asciiz "atr8.tgi"
+        .endif
diff --git a/src/Makefile b/src/Makefile
index 7e6964579..051c7eb1f 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -12,19 +12,14 @@ PROGS = ar65  \
         sim65 \
         sp65
 
-ifdef prefix
-  CA65_INC = $(prefix)/lib/cc65/asminc
-  CC65_INC = $(prefix)/lib/cc65/include
-  LD65_LIB = $(prefix)/lib/cc65/lib
-  LD65_OBJ = $(prefix)/lib/cc65/lib
-  LD65_CFG = $(prefix)/lib/cc65/cfg
-else
-  CA65_INC := $(abspath ../asminc)
-  CC65_INC := $(abspath ../include)
-  LD65_LIB := $(abspath ../lib)
-  LD65_OBJ := $(abspath ../lib)
-  LD65_CFG := $(abspath ../cfg)
-endif
+bindir  := $(prefix)/bin
+datadir := $(if $(prefix),$(prefix)/share/cc65,$(abspath ..))
+
+CA65_INC = $(datadir)/asminc
+CC65_INC = $(datadir)/include
+LD65_LIB = $(datadir)/lib
+LD65_OBJ = $(datadir)/lib
+LD65_CFG = $(datadir)/cfg
 
 CFLAGS += -MMD -MP -O -std=c89 -I common \
           -Wall -Wextra -Wno-char-subscripts -Werror $(USER_CFLAGS) \
@@ -33,9 +28,11 @@ CFLAGS += -MMD -MP -O -std=c89 -I common \
 
 LDLIBS += -lm
 
+INSTALL = install
+
 .SUFFIXES:
 
-.PHONY: all bin $(PROGS) mostlyclean clean avail unavail
+.PHONY: all bin $(PROGS) mostlyclean clean install avail unavail
 
 all bin: $(PROGS)
 
@@ -45,6 +42,11 @@ mostlyclean:
 clean:
 	$(RM) -r ../wrk ../bin
 
+install:
+	$(if $(prefix),,$(error variable `prefix' must be set))
+	$(INSTALL) -d $(DESTDIR)$(bindir)
+	$(INSTALL) ../bin/* $(DESTDIR)$(bindir)
+
 avail:
 	$(foreach prog,$(PROGS),$(AVAIL_recipe))