From dab3db05a2dece9d5c0a2d4d06ed015cb6f397a6 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Asbj=C3=B8rn=20Djupdal?= <asbjorn.djupdal@computerwell.com>
Date: Fri, 9 Oct 2026 08:46:57 +0200
Subject: [PATCH] CBM GEOS desk accessory support

This provides support for creating desk accessories for C64/C128 GEOS.
A working sample is provided, demonstrating that this works.
A new target is created: geos-c-da
This implements issue #823.
---
 cfg/geos-c-da.cfg           |  49 +++++++++
 doc/grc65.sgml              |  14 ++-
 include/geos/gsys.h         |   1 +
 libsrc/Makefile             |  11 +-
 libsrc/geos-c-da/crt0.s     |  76 +++++++++++++
 samples/geos/Makefile       |   6 ++
 samples/geos/deskacc.c      | 210 ++++++++++++++++++++++++++++++++++++
 samples/geos/deskaccres.grc |  24 +++++
 src/ca65/main.c             |   1 +
 src/cc65/main.c             |   1 +
 src/common/target.c         |   2 +
 src/common/target.h         |   1 +
 src/grc65/main.c            |  98 ++++++++++++-----
 13 files changed, 461 insertions(+), 33 deletions(-)
 create mode 100644 cfg/geos-c-da.cfg
 create mode 100644 libsrc/geos-c-da/crt0.s
 create mode 100644 samples/geos/deskacc.c
 create mode 100644 samples/geos/deskaccres.grc

diff --git a/cfg/geos-c-da.cfg b/cfg/geos-c-da.cfg
new file mode 100644
index 000000000..a11b637a7
--- /dev/null
+++ b/cfg/geos-c-da.cfg
@@ -0,0 +1,49 @@
+FEATURES {
+    STARTADDRESS: default = $1000;
+}
+SYMBOLS {
+    __BACKBUFSIZE__:    type = weak, value = $2000;
+    __STACKSIZE__:      type = weak, value = $0400; # 1k stack
+    __STACKADDR__:      type = weak, value = __VLIR0_LAST__;
+    __SAVEDZPADDR__:    type = weak, value = __STACKADDR__ + __STACKSIZE__;
+    __HIMEM__:          type = weak, value = __SAVEDZPADDR__ + __ZP_SIZE__;
+    __VLIR0_BLOCKS__:   type = export, value = ((__VLIR0_LAST__ - __VLIR0_START__ - __BSS_SIZE__) + 253) / 254;
+}
+MEMORY {
+    CVT:      file   = %O,  start = $0,               size = $40000;
+    ZP:       define = yes, start = $58,               size = $1A + $06;
+
+    VLIR0:    define = yes, start = %S,                size = ($6000 - %S) - __STACKSIZE__ - __ZP_SIZE__;
+    SAVEDZP:  define = yes, start = __SAVEDZPADDR__,   size = __ZP_SIZE__;
+}
+SEGMENTS {
+    ZEROPAGE:  type = zp,  load = ZP;
+    EXTZP:     type = zp,  load = ZP,                                   optional = yes;
+    DIRENTRY:  type = ro,                 load = CVT, align      = $FE;
+    FILEINFO:  type = ro,                 load = CVT, align      = $FE;
+    RECORDS:   type = ro,                 load = CVT, align      = $FE, optional = yes;
+    STARTUP:   type = ro,  run  = VLIR0,  load = CVT, align_load = $FE, define   = yes;
+    LOWCODE:   type = ro,  run  = VLIR0,  load = CVT,                   optional = yes;
+    ONCE:      type = ro,  run  = VLIR0,  load = CVT,                   optional = yes;
+    CODE:      type = ro,  run  = VLIR0,  load = CVT;
+    RODATA:    type = ro,  run  = VLIR0,  load = CVT;
+    DATA:      type = rw,  run  = VLIR0,  load = CVT;
+    INIT:      type = bss, load = VLIR0,                                optional = yes;
+    BSS:       type = bss, load = VLIR0,                                define   = yes;
+    SAVEDZP:   type = bss, load = SAVEDZP;
+}
+FEATURES {
+    CONDES: type    = constructor,
+            label   = __CONSTRUCTOR_TABLE__,
+            count   = __CONSTRUCTOR_COUNT__,
+            segment = ONCE;
+    CONDES: type    = destructor,
+            label   = __DESTRUCTOR_TABLE__,
+            count   = __DESTRUCTOR_COUNT__,
+            segment = RODATA;
+    CONDES: type    = interruptor,
+            label   = __INTERRUPTOR_TABLE__,
+            count   = __INTERRUPTOR_COUNT__,
+            segment = RODATA,
+            import  = __CALLIRQ__;
+}
diff --git a/doc/grc65.sgml b/doc/grc65.sgml
index d256c31e6..2ab88f7f5 100644
--- a/doc/grc65.sgml
+++ b/doc/grc65.sgml
@@ -24,8 +24,9 @@ Optional resources might be menu definitions, other headers (e.g., for data
 files of an app.), dialog definitions, etc.  Without an application's header,
 GEOS is unable to load and start it.
 
-Currently, <bf/grc65/ supports only menus and the required header definition,
-along with support for building applications with VLIR-structured overlays.
+Currently, <bf/grc65/ supports menus, the required header definition,
+driver/accessory headers (desk accessories), and building applications with
+VLIR-structured overlays.
 
 <bf/grc65/ generates output in two formats: C header and <bf/ca65/ source (.s).
 That is because the application header data must be in assembly format, while
@@ -115,7 +116,8 @@ HEADER <GEOS_TYPE> "dosname" "classname" "version" {
 }</verb></tscreen>
 The header definition describes the GEOS header sector which is unique to
 each file.  The definition starts with the keyword <tt/HEADER/, then goes the
-GEOS file-type.  You can use only <tt/APPLICATION/ here at the moment.  Then,
+GEOS file-type.  It can be <tt/APPLICATION/, <tt/AUTO_EXEC/, or <tt/DESK_ACC/.
+Then,
 there are (each one in quotes) the DOS file-name (up to 16 characters), the GEOS
 Class name (up to 12 characters), and the version info (up to 4 characters).
 The version should be written as &dquot;<tt/V/x.y&dquot;, where <em/x/ is the
@@ -266,6 +268,12 @@ required for the correct process of GEOS sequential application building.
 
 
 
+<sect>Building desk accessories<label id="building-da">
+<p>Desk accessories (<tt/DESK_ACC/) must be built using the following target: <tt/geos-c-da/
+
+See <tt>samples/geos</tt> for a working example.
+
+
 <sect>Building a GEOS VLIR overlay application<label id="building-vlir">
 <p>Large GEOS applications typically don't fit in one piece in their designated
 memory area.  They are therefore split into overlays which are loaded into memory
diff --git a/include/geos/gsys.h b/include/geos/gsys.h
index 1753492e5..796f274b5 100644
--- a/include/geos/gsys.h
+++ b/include/geos/gsys.h
@@ -12,6 +12,7 @@ void InitForIO(void);
 void DoneWithIO(void);
 void MainLoop(void);
 void EnterDeskTop(void);
+void RstrAppl(void);
 void ToBASIC(void);
 void Panic(void);
 
diff --git a/libsrc/Makefile b/libsrc/Makefile
index ee63f2c80..228773ed1 100644
--- a/libsrc/Makefile
+++ b/libsrc/Makefile
@@ -31,7 +31,8 @@ CBMS = c128   \
        vic20
 
 GEOS = geos-apple \
-       geos-cbm
+       geos-cbm   \
+       geos-c-da
 
 TARGETS = agat         \
           apple2       \
@@ -191,18 +192,24 @@ else ifeq ($(TARGET),atarixl)
   DRVPFX = atrx
 else ifeq ($(TARGET),sim65c02)
   SRCDIR = sim6502
+else ifeq ($(TARGET),geos-c-da)
+  SRCDIR = geos-cbm
 else
   SRCDIR = $(TARGET)
 endif
 
 SRCDIRS = $(SRCDIR)
 
+ifeq ($(TARGET),geos-c-da)
+  SRCDIRS := geos-c-da $(SRCDIRS)
+endif
+
 ifeq ($(TARGET),$(filter $(TARGET),$(CBMS)))
   SRCDIRS += cbm
 endif
 
 ifeq ($(TARGET),$(filter $(TARGET),$(GEOS)))
-  SRCDIRS += $(addprefix $(TARGET)/,  $(GEOSDIRS))
+  SRCDIRS += $(addprefix $(SRCDIR)/,  $(GEOSDIRS))
   SRCDIRS += $(addprefix geos-common/,$(GEOSDIRS))
 endif
 
diff --git a/libsrc/geos-c-da/crt0.s b/libsrc/geos-c-da/crt0.s
new file mode 100644
index 000000000..7ce8193fc
--- /dev/null
+++ b/libsrc/geos-c-da/crt0.s
@@ -0,0 +1,76 @@
+;
+; Startup code for a GEOS desk accessory (DESK_ACC), based on
+; libsrc/geos-common/system/crt0.s
+;
+
+            .export _exit
+            .export __STARTUP__ : absolute = 1          ; Mark as startup
+            .export __GEOS_SAVED_ZP__
+            .export _RstrAppl
+            .import __STACKADDR__, __STACKSIZE__        ; Linker generated
+            .import __ZP_START__, __ZP_SIZE__           ; Linker generated
+            .import initlib, donelib
+            .import callmain
+            .import zerobss
+            .importzp c_sp
+
+            .include "jumptab.inc"
+
+; ------------------------------------------------------------------------
+; Somewhere to save cc65's own runtime zero page block while this
+; accessory is running.
+
+.segment        "SAVEDZP"
+
+__GEOS_SAVED_ZP__:
+
+; ------------------------------------------------------------------------
+; Place the startup code in a special segment.
+
+.segment        "STARTUP"
+
+; Save zero page before anything below gets a chance to use it.
+
+        ldy #<(__ZP_SIZE__ - 1)
+SaveZP: lda __ZP_START__,y
+        sta __GEOS_SAVED_ZP__,y
+        dey
+        bpl SaveZP
+
+; Clear the BSS data.
+
+        jsr zerobss
+
+; Set up the stack.
+
+        lda #<(__STACKADDR__ + __STACKSIZE__)
+        ldx #>(__STACKADDR__ + __STACKSIZE__)
+        sta c_sp
+        stx c_sp+1
+
+; Call the module constructors.
+
+        jsr initlib
+
+; Push the command-line arguments; and, call main().
+
+        jsr callmain
+
+; Call the module destructors, then leave this DA and resume the
+; calling application, restoring cc65's own runtime zero page block
+; first. Whether main() just returned or RstrAppl() was called
+; explicitly, both need to happen the same way, so _exit and _RstrAppl
+; are the same code.
+
+_exit:
+_RstrAppl:
+        jsr donelib
+
+        ldy #<(__ZP_SIZE__ - 1)
+RestoreZP:
+        lda __GEOS_SAVED_ZP__,y
+        sta __ZP_START__,y
+        dey
+        bpl RestoreZP
+
+        jmp RstrAppl
diff --git a/samples/geos/Makefile b/samples/geos/Makefile
index 1443d9709..905f73e19 100644
--- a/samples/geos/Makefile
+++ b/samples/geos/Makefile
@@ -79,6 +79,7 @@ endef # SUBDIR_recipe
 
 EXELIST_geos-cbm = \
 	bitmap-demo.cvt \
+	deskacc.cvt \
 	filesel.cvt \
 	geosver.cvt \
 	getid.cvt \
@@ -172,9 +173,14 @@ yesno.cvt: yesnores.grc yesno.c
 	$(if $(QUIET),echo $(SYS):$@)
 	$(CL) -t $(SYS) -O -o $@ -m yesno.map yesnores.grc yesno.c
 
+deskacc.cvt: deskaccres.grc deskacc.c
+	$(if $(QUIET),echo $(SYS):$@)
+	$(CL) -t geos-c-da -O -o $@ -m deskacc.map deskaccres.grc deskacc.c
+
 
 clean:
 	@$(DEL) overlay-demores.h 2>$(NULLDEV)
+	@$(DEL) deskaccres.h 2>$(NULLDEV)
 	@$(DEL) bitmap.c 2>$(NULLDEV)
 	@$(DEL) *.cvt 2>$(NULLDEV)
 	@$(DEL) *.map 2>$(NULLDEV)
diff --git a/samples/geos/deskacc.c b/samples/geos/deskacc.c
new file mode 100644
index 000000000..63f8dfd20
--- /dev/null
+++ b/samples/geos/deskacc.c
@@ -0,0 +1,210 @@
+/*
+** Desk accessory example, replicating the behaviour of the sample desk
+** accessory shipped with GeoProgrammer
+**
+** 2026, Asbjørn Djupdal (asbjoern@djupdal.org)
+*/
+
+#include <stdbool.h>
+#include <geos.h>
+
+#include "deskaccres.h"
+
+/*****************************************************************************/
+/* defines */
+
+/* screen region this accessory uses, in cards */
+#define DA_TOP      8
+#define DA_LEFT     10
+#define DA_HEIGHT   8
+#define DA_WIDTH    20
+
+#define NUM_CARDS   (DA_HEIGHT * DA_WIDTH)
+
+#define COLOR_MATRIX_BASE ((char *) 0x8c00)
+
+#define CARD_ADDR(base, cardRow, cardCol) \
+    ((base) + (unsigned) (cardRow) * (40 * 8) + (unsigned) (cardCol) * 8)
+
+/*****************************************************************************/
+/* variables */
+
+static char recoverFlag;
+static char colorBuf[NUM_CARDS];
+static char foreBuf[NUM_CARDS * 8];
+static char backBuf[NUM_CARDS * 8];
+
+/*****************************************************************************/
+/* icon */
+
+static const unsigned char iconPicture[] = {
+    0x06, 0xFF, 0x81, 0x80, 0x04, 0x00, 0x82, 0x01,
+    0x80, 0x04, 0x00, 0x82, 0x01, 0x80, 0x04, 0x00,
+    0x82, 0x01, 0x80, 0x04, 0x00, 0x82, 0x01, 0x80,
+    0x04, 0x00, 0xBE, 0x01, 0x80, 0x0E, 0x00, 0x00,
+    0x00, 0x01, 0x80, 0x04, 0x00, 0x00, 0x00, 0x01,
+    0x80, 0x04, 0x00, 0x00, 0x00, 0x01, 0x80, 0x04,
+    0x38, 0x63, 0x60, 0x01, 0x80, 0x04, 0x4C, 0x91,
+    0x90, 0x01, 0x80, 0x04, 0x41, 0x09, 0x10, 0x01,
+    0x80, 0x04, 0x41, 0x09, 0x10, 0x01, 0x80, 0x04,
+    0x41, 0x09, 0x10, 0x01, 0x80, 0x04, 0x44, 0x91,
+    0x10, 0x01, 0x80, 0x0E, 0x38, 0x63, 0xB8, 0x01,
+    0x80, 0x04, 0x00, 0x82, 0x01, 0x80, 0x04, 0x00,
+    0x82, 0x01, 0x80, 0x04, 0x00, 0x82, 0x01, 0x80,
+    0x04, 0x00, 0x82, 0x01, 0x80, 0x04, 0x00, 0x82,
+    0x01, 0x80, 0x04, 0x00, 0x81, 0x01, 0x06, 0xFF
+};
+
+void DoIcon1 (void);
+
+static const struct icontab icon = {
+    1,
+    { DA_LEFT * 8, DA_TOP * 8 },
+    {
+        { (char *) iconPicture, DA_LEFT + 3, DA_TOP * 8 + 24, 6, 23,
+          (unsigned) DoIcon1 }
+    }
+};
+
+/*****************************************************************************/
+/* framed box */
+
+static const graphicStr drawBox = {
+    NEWPATTERN (0),                       /* white */
+    MOVEPENTO (DA_LEFT * 8, DA_TOP * 8),
+    RECTANGLETO ((DA_LEFT + DA_WIDTH) * 8 - 1, (DA_TOP + DA_HEIGHT) * 8 - 1),
+    NEWPATTERN (1),                       /* black */
+    FRAME_RECTO (DA_LEFT * 8, DA_TOP * 8),
+    GSTR_END
+};
+
+/*****************************************************************************/
+/* functions */
+
+/* copy this accessory's screen area, one card at a time, between the given
+** screen bitmap and the given RAM buffer.
+*/
+static void CopyBitmap (char *screen, char *buf, bool toBuf)
+{
+    char row, col, i;
+    char *card;
+
+    for (row = 0; row < DA_HEIGHT; ++row) {
+        for (col = 0; col < DA_WIDTH; ++col) {
+            card = CARD_ADDR (screen, DA_TOP + row, DA_LEFT + col);
+            for (i = 0; i < 8; ++i) {
+                if (toBuf) {
+                    *buf++ = card[i];
+                } else {
+                    card[i] = *buf++;
+                }
+            }
+        }
+    }
+}
+
+/* save screen buffers */
+static void SaveScreen (void)
+{
+    CopyBitmap (BACK_SCR_BASE, backBuf, true);
+
+    if (recoverFlag & 0x80) {
+        CopyBitmap (SCREEN_BASE, foreBuf, true);
+    }
+}
+
+/* restore screen buffers */
+static void RestoreScreen (void)
+{
+    CopyBitmap (BACK_SCR_BASE, backBuf, false);
+
+    if (recoverFlag & 0x80) {
+        CopyBitmap (SCREEN_BASE, foreBuf, false);
+    }
+}
+
+/* save color values */
+static void SaveColors (void)
+{
+    char row, col, fillColor;
+
+    fillColor = COLOR_MATRIX_BASE[39];
+
+    for (row = 0; row < DA_HEIGHT; ++row) {
+        for (col = 0; col < DA_WIDTH; ++col) {
+            if (recoverFlag & 0x40) {
+                colorBuf[row * DA_WIDTH + col] =
+                    COLOR_MATRIX_BASE[(DA_TOP + row) * 40 + DA_LEFT + col];
+            }
+            COLOR_MATRIX_BASE[(DA_TOP + row) * 40 + DA_LEFT + col] = fillColor;
+        }
+    }
+}
+
+/* restore color values */
+static void RestoreColors (void)
+{
+    char row, col;
+
+    for (row = 0; row < DA_HEIGHT; ++row) {
+        for (col = 0; col < DA_WIDTH; ++col) {
+            COLOR_MATRIX_BASE[(DA_TOP + row) * 40 + DA_LEFT + col] =
+                colorBuf[row * DA_WIDTH + col];
+        }
+    }
+}
+
+/*****************************************************************************/
+/* handlers */
+
+void DoClose (void)
+{
+    GotoFirstMenu ();
+}
+
+void DoCut (void)
+{
+    GotoFirstMenu ();
+}
+
+void DoCopy (void)
+{
+    GotoFirstMenu ();
+}
+
+void DoPaste (void)
+{
+    GotoFirstMenu ();
+}
+
+void DoIcon1 (void)
+{
+}
+
+void DoQuit (void)
+{
+    GotoFirstMenu ();
+    if (recoverFlag & 0x40) {
+        RestoreColors ();
+    }
+    RestoreScreen ();
+    RstrAppl ();
+}
+
+/*****************************************************************************/
+
+void main (void)
+{
+    recoverFlag = r10L;
+
+    SaveScreen ();
+    SaveColors ();
+
+    dispBufferOn = ST_WR_FORE | ST_WR_BACK;
+
+    GraphicsString (&drawBox);
+    DoMenu ((struct menu *) &mainMenu);
+    DoIcons ((struct icontab *) &icon);
+
+    MainLoop ();
+}
diff --git a/samples/geos/deskaccres.grc b/samples/geos/deskaccres.grc
new file mode 100644
index 000000000..2f06df06e
--- /dev/null
+++ b/samples/geos/deskaccres.grc
@@ -0,0 +1,24 @@
+MENU fileSubMenu 80,79 VERTICAL
+{
+    "close" MENU_ACTION DoClose
+    "quit" MENU_ACTION DoQuit
+}
+
+MENU editSubMenu 100,79 VERTICAL
+{
+    "cut" MENU_ACTION DoCut
+    "copy" MENU_ACTION DoCopy
+    "paste" MENU_ACTION DoPaste
+}
+
+MENU mainMenu 80,64 HORIZONTAL
+{
+    "file" SUB_MENU fileSubMenu
+    "edit" SUB_MENU editSubMenu
+}
+
+HEADER DESK_ACC "deskacc" "DeskAcc Demo" "V1.0" {
+    dostype USR
+    info "Sample desk accessory"
+    mode 40only
+}
diff --git a/src/ca65/main.c b/src/ca65/main.c
index 8dd5c2aa5..bb8b7f4cf 100644
--- a/src/ca65/main.c
+++ b/src/ca65/main.c
@@ -333,6 +333,7 @@ static void SetSys (const char* Sys)
             NewSymbol ("__GAMATE__", 1);
             break;
 
+        case TGT_GEOS_CBM_DA:
         case TGT_GEOS_CBM:
             /* Do not handle as a CBM system */
             NewSymbol ("__GEOS__", 1);
diff --git a/src/cc65/main.c b/src/cc65/main.c
index c12aa1bbe..a631b8cc1 100644
--- a/src/cc65/main.c
+++ b/src/cc65/main.c
@@ -243,6 +243,7 @@ static void SetSys (const char* Sys)
             DefineNumericMacro ("__GAMATE__", 1);
             break;
 
+        case TGT_GEOS_CBM_DA:
         case TGT_GEOS_CBM:
             /* Do not handle as a CBM system */
             DefineNumericMacro ("__GEOS__", 1);
diff --git a/src/common/target.c b/src/common/target.c
index 64b2d3d85..4ca5ac4e2 100644
--- a/src/common/target.c
+++ b/src/common/target.c
@@ -185,6 +185,7 @@ static const TargetEntry TargetMap[] = {
     {   "gamate",       TGT_GAMATE       },
     {   "geos",         TGT_GEOS_CBM     },
     {   "geos-apple",   TGT_GEOS_APPLE   },
+    {   "geos-c-da",    TGT_GEOS_CBM_DA  },
     {   "geos-cbm",     TGT_GEOS_CBM     },
     {   "kim1",         TGT_KIM1         },
     {   "lunix",        TGT_LUNIX        },
@@ -251,6 +252,7 @@ static const TargetProperties PropertyTable[TGT_COUNT] = {
     { "kim1",           CPU_6502,       BINFMT_BINARY,      CTNone  },
     { "rp6502",         CPU_W65C02,     BINFMT_BINARY,      CTNone  },
     { "agat",           CPU_6502,       BINFMT_BINARY,      CTAgat  },
+    { "geos-c-da",      CPU_6502,       BINFMT_BINARY,      CTNone  },
 };
 
 /* Target system */
diff --git a/src/common/target.h b/src/common/target.h
index 86c3132ff..37b224285 100644
--- a/src/common/target.h
+++ b/src/common/target.h
@@ -93,6 +93,7 @@ typedef enum {
     TGT_KIM1,
     TGT_RP6502,
     TGT_AGAT,
+    TGT_GEOS_CBM_DA,
     TGT_COUNT                   /* Number of target systems */
 } target_t;
 
diff --git a/src/grc65/main.c b/src/grc65/main.c
index 9dce48c28..fb0ea1b5f 100644
--- a/src/grc65/main.c
+++ b/src/grc65/main.c
@@ -148,6 +148,7 @@ static void OptTarget (const char* Opt attribute ((unused)), const char* Arg)
 {
     switch (FindTarget (Arg)) {
 
+        case TGT_GEOS_CBM_DA:
         case TGT_GEOS_CBM:
             apple = 0;
             break;
@@ -462,6 +463,7 @@ static void DoHeader (void)
     char *token;
     char i1[9], i2[9], i3[9];
     int i;
+    int isDeskAcc = 0;
 
     openSFile ();
 
@@ -471,20 +473,28 @@ static void DoHeader (void)
 
     if (apple == 1) {
         switch (i) {
-            case 0:
+            case 0: /* APPLICATION */
                 myHead.geostype = 0x82;
                 break;
+            case 2: /* DESK_ACC */
+                myHead.geostype = 0x81;
+                isDeskAcc = 1;
+                break;
             default:
                 AbEnd ("Filetype '%s' is not supported yet", token);
         }
     } else {
         switch (i) {
-            case 0:
+            case 0: /* APPLICATION */
                 myHead.geostype = 6;
                 break;
-            case 1:
+            case 1: /* AUTO_EXEC */
                 myHead.geostype = 14;
                 break;
+            case 2: /* DESK_ACC */
+                myHead.geostype = 5;
+                isDeskAcc = 1;
+                break;
             default:
                 AbEnd ("Filetype '%s' is not supported yet", token);
         }
@@ -597,31 +607,46 @@ static void DoHeader (void)
 
     /* OK, all information is gathered, do flushout */
 
+    if (isDeskAcc) {
+        /* The end address for a desk accessory must cover the whole memory
+        ** range GEOS has to save and restore.  __HIMEM__ is used for this
+        */
+        fprintf (outputSFile,
+            "    .import __HIMEM__\n");
+    }
+
     fprintf (outputSFile,
         "    .import __BSS_SIZE__, __STARTUP_RUN__\n"
         "    .import __VLIR0_START__, __VLIR0_LAST__\n"
         "    .import __VLIR0_BLOCKS__\n"
-        "    .import __VLIR1_BLOCKS__\n"
-        "    .import __VLIR2_BLOCKS__\n"
-        "    .import __VLIR3_BLOCKS__\n"
-        "    .import __VLIR4_BLOCKS__\n"
-        "    .import __VLIR5_BLOCKS__\n"
-        "    .import __VLIR6_BLOCKS__\n"
-        "    .import __VLIR7_BLOCKS__\n"
-        "    .import __VLIR8_BLOCKS__\n"
-        "    .import __VLIR9_BLOCKS__\n"
-        "    .import __VLIR10_BLOCKS__\n"
-        "    .import __VLIR11_BLOCKS__\n"
-        "    .import __VLIR12_BLOCKS__\n"
-        "    .import __VLIR13_BLOCKS__\n"
-        "    .import __VLIR14_BLOCKS__\n"
-        "    .import __VLIR15_BLOCKS__\n"
-        "    .import __VLIR16_BLOCKS__\n"
-        "    .import __VLIR17_BLOCKS__\n"
-        "    .import __VLIR18_BLOCKS__\n"
-        "    .import __VLIR19_BLOCKS__\n\n"
     );
 
+    if (myHead.structure == APPHEADER_STRUCTURE_VLIR) {
+        fprintf (outputSFile,
+            "    .import __VLIR1_BLOCKS__\n"
+            "    .import __VLIR2_BLOCKS__\n"
+            "    .import __VLIR3_BLOCKS__\n"
+            "    .import __VLIR4_BLOCKS__\n"
+            "    .import __VLIR5_BLOCKS__\n"
+            "    .import __VLIR6_BLOCKS__\n"
+            "    .import __VLIR7_BLOCKS__\n"
+            "    .import __VLIR8_BLOCKS__\n"
+            "    .import __VLIR9_BLOCKS__\n"
+            "    .import __VLIR10_BLOCKS__\n"
+            "    .import __VLIR11_BLOCKS__\n"
+            "    .import __VLIR12_BLOCKS__\n"
+            "    .import __VLIR13_BLOCKS__\n"
+            "    .import __VLIR14_BLOCKS__\n"
+            "    .import __VLIR15_BLOCKS__\n"
+            "    .import __VLIR16_BLOCKS__\n"
+            "    .import __VLIR17_BLOCKS__\n"
+            "    .import __VLIR18_BLOCKS__\n"
+            "    .import __VLIR19_BLOCKS__\n"
+        );
+    }
+
+    fprintf (outputSFile, "\n");
+
     fprintf (outputSFile,
         "    .segment \"DIRENTRY\"\n\n");
 
@@ -674,12 +699,22 @@ static void DoHeader (void)
              * add size of each VLIR segment, plus 1 block for the info block (icon),
              * plus another block for the VLIR RECORDS table (VLIR structure only)
              */
-            "    .word %d + __VLIR0_BLOCKS__ + __VLIR1_BLOCKS__ + __VLIR2_BLOCKS__ + __VLIR3_BLOCKS__ + __VLIR4_BLOCKS__ + __VLIR5_BLOCKS__ + __VLIR6_BLOCKS__ + __VLIR7_BLOCKS__ + __VLIR8_BLOCKS__ + __VLIR9_BLOCKS__ + __VLIR10_BLOCKS__ + __VLIR11_BLOCKS__ + __VLIR12_BLOCKS__ + __VLIR13_BLOCKS__ + __VLIR14_BLOCKS__ + __VLIR15_BLOCKS__ + __VLIR16_BLOCKS__ + __VLIR17_BLOCKS__ + __VLIR18_BLOCKS__ + __VLIR19_BLOCKS__\n"
-            /* PRG formatted or SEQ formatted */
-            "    .byte \"%s formatted GEOS file V1.0\"\n\n",
+            "    .word %d + __VLIR0_BLOCKS__",
             myHead.structure, myHead.geostype,
             myHead.year, myHead.month, myHead.day, myHead.hour, myHead.min,
-            (myHead.structure == APPHEADER_STRUCTURE_SEQ) ? 1 : 2,
+            (myHead.structure == APPHEADER_STRUCTURE_SEQ) ? 1 : 2
+        );
+
+        if (myHead.structure == APPHEADER_STRUCTURE_VLIR) {
+            fprintf (outputSFile,
+                " + __VLIR1_BLOCKS__ + __VLIR2_BLOCKS__ + __VLIR3_BLOCKS__ + __VLIR4_BLOCKS__ + __VLIR5_BLOCKS__ + __VLIR6_BLOCKS__ + __VLIR7_BLOCKS__ + __VLIR8_BLOCKS__ + __VLIR9_BLOCKS__ + __VLIR10_BLOCKS__ + __VLIR11_BLOCKS__ + __VLIR12_BLOCKS__ + __VLIR13_BLOCKS__ + __VLIR14_BLOCKS__ + __VLIR15_BLOCKS__ + __VLIR16_BLOCKS__ + __VLIR17_BLOCKS__ + __VLIR18_BLOCKS__ + __VLIR19_BLOCKS__"
+            );
+        }
+
+        fprintf (outputSFile,
+            "\n"
+            /* PRG formatted or SEQ formatted */
+            "    .byte \"%s formatted GEOS file V1.0\"\n\n",
             (myHead.structure == APPHEADER_STRUCTURE_SEQ) ? "SEQ" : "PRG"
         );
     }
@@ -702,8 +737,15 @@ static void DoHeader (void)
 
     fprintf (outputSFile,
         "    .byte %i, %i, %i\n"
-        "    .word __VLIR0_START__, __VLIR0_START__ - 1, __STARTUP_RUN__\n\n",
-        myHead.dostype, myHead.geostype, myHead.structure);
+        "    .word __VLIR0_START__, %s, __STARTUP_RUN__\n\n",
+        myHead.dostype, myHead.geostype, myHead.structure,
+        /* For desk accessories, GEOS computes the memory range to back up
+        ** and restore as (end address - start address), i.e. end address
+        ** is exclusive. Every other file type uses the documented
+        ** "start address - 1" dummy convention instead (this field isn't
+        ** meaningful for them).
+        */
+        isDeskAcc ? "__HIMEM__" : "__VLIR0_START__ - 1");
 
     fillOut (myHead.classname, 12, "$20");