Add CARTSIZE to cfg file for configuring the a78 header. Add descriptions of usage.

cfg/atari7800.cfg

@@ -1,7 +1,12 @@
 # Atari VCS 7800 linker configuration file for cc65
+# This cfg file adds the a78 header in front of the image
+# If you want just the ROM you can mark the __EXEHDR__ as weak instead of import
+# But for the most common use we add the a78 automatically as it
+# contains info about what kind of cart the build supports
 
 SYMBOLS {
-    __STACKSIZE__:        type = weak, value = $0010; # 16 bytes stack
+    __STACKSIZE__:        type = weak, value = $0600; # C stack
+    __CARTSIZE__:         type = weak, value = $c000;
     __EXEHDR__:           type = import;
     __VEC_BOTTOM__:       value = $fffa, type = export;
     __VEC_SIZE__:         value = $6, type = export;
@@ -37,7 +42,7 @@ MEMORY {
 
 SEGMENTS {
     ZEROPAGE:   load = ZP,              type = zp;
-    EXEHDR:     load = HEADER,          type = ro,  define = yes;
+    EXEHDR:     load = HEADER,          type = ro;
     STARTUP:    load = ROMS,             type = ro,  define = yes;
     ONCE:       load = ROMS,             type = ro,  define = yes;
     CODE:       load = ROM,             type = ro,  define = yes;

doc/atari7800.sgml

@@ -24,7 +24,29 @@ comes with the cc65 C compiler. It describes the memory layout, Atari
 <sect>Binary format<p>
 
 The default binary output format generated by the linker for the Atari
-7800 target is a 32K cartridge image.
+7800 target is a 48K cartridge image.
+
+<sect>A78 header<p>
+
+There is lots of different cart hardware available for the atari7800.
+Some carts have ROM, RAM, sound hardware, non-volatile high score chips.
+In order to know what kind of hardware the cart build requires there is
+a header file of 128 bytes in front of the binary.
+
+The default build creates a cart file for a 48K rom cart without any
+extra features like the pokey audio chip or extra RAM.
+
+In order to make cc65 more user friendly the build will add the a78
+header automatically. This allows you to run the binary on emulators
+and flash carts on the real console.
+
+<sect>Encryption<p>
+
+In order to boot the game in a mode that supports atari7800 functions
+the cart must be encrypted after the linking phase.
+There is a program called sign7800 that can be used to sign the cart.
+The encryption is not required for running the cart on emulators.
+You can also run atari2600 games without encryption.
 
 <sect>Memory layout<p>
 
@@ -104,12 +126,6 @@ There are no drivers for the Atari 7800.
 TBD
 
 
-<sect>Encryption<p>
-
-In order to boot the game in a mode that supports atari7800 functions
-the cart must be encrypted after the linking phase.
-There is a program called sign7800 that can be used to sign the cart.
-
 <sect>Other hints<p>
 
 One may write a custom linker configuration file to tune the memory

libsrc/atari7800/exehdr.s

@@ -4,7 +4,7 @@
 ; This header contains data for emulators
 ;
         .export         __EXEHDR__: absolute = 1
-
+        .import		__CARTSIZE__
 ; ------------------------------------------------------------------------
 ; EXE header
 	.segment "EXEHDR"
@@ -12,7 +12,7 @@
 	.byte	'A','T','A','R','I','7','8','0','0',' ',' ',' ',' ',' ',' ',' '
 	.byte	'G','a','m','e',' ','n','a','m','e',0,0,0,0,0,0,0
 	.byte	0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
-	.byte	0,0,$80,0					; Size
+	.byte	0,0,>__CARTSIZE__,0			; Set the cart size in the cfg file
     ;    bit  0 - pokey at 4000
     ;    bit  1 - supergame bank switched
     ;    bit  2 - supergame ram at $4000