<sect1>Function keys<p>
-These are defined to be Atari + number key.
+Function keys are mapped to Atari + number key.
<sect1>Reserving a memory area inside a program<label id="memhole"><p>
The Atari 130XE maps its additional memory into CPU memory in 16K
chunks at address $4000 to $7FFF. One might want to
prevent this memory area from being used by cc65. Other reasons to
-prevent the use of some memory area could be the buffers for display
-lists and screen memory.
+prevent the use of some memory area could be to reserve space for the
+buffers for display lists and screen memory.
<p>
The Atari executable format allows holes inside a program, e.g. one
part loads into $2E00 to $3FFF, going below the reserved
$BC1F.
<p>
Each load chunk of the executable starts with a 4 byte header which
-defines its load address and size.
+defines its load address and size. In the following linker scripts
+these headers are named HEADER and SECHDR (for the MEMORY layout), and
+accordingly NEXEHDR and CHKHDR (for the SEGMENTS layout).
<p>
<sect2>Low code and high data example<p>
Goal: Create an executable with 2 load chunks which doesn't use the
<p>
The main problem is that the EXE header generated by the cc65 runtime
lib is wrong. It defines a single load chunk with the sizes/addresses
-of the LOWCODE, INIT, CODE, RODATA, and DATA segments (the whole user
+of the STARTUP, LOWCODE, INIT, CODE, RODATA, and DATA segments (the whole user
program).
<p>
The contents of the EXE header come from the EXEHDR segment, which is
-defined in crt0.s. This cannot be changed w/o modifying and
+defined in crt0.s. This cannot be changed without modifying and
recompiling the cc65 atari runtime lib. Therefore the original EXE
header must be discarded. It will be replaced by a user created
-one.
+one. The discarding is done by assigning the EXEHDR segment to the
+BANK memory area. The BANK memory area is discarded in the new linker
+script (written to file "").
<p>
The user needs to create a customized linker config file which adds
new memory areas and segments to hold the new EXE header and the
and the second load chunk header.
<p>
<p>
-This is a modified cc65 Atari linker configuration file (split.cfg):
+This is an example of a modified cc65 Atari linker configuration file
+(split.cfg):
<tscreen><verb>
+SYMBOLS {
+ __STACKSIZE__ = $800; # 2K stack
+ __RESERVED_MEMORY__: value = $0000, weak = yes;
+}
+FEATURES {
+ STARTADDRESS: default = $2E00;
+}
MEMORY {
ZP: start = $82, size = $7E, type = rw, define = yes;
HEADER: start = $0000, size = $6, file = %O; # first load chunk
- RAMLO: start = $2E00, size = $1200, file = %O;
+ RAMLO: start = %S, size = $4000 - %S, file = %O;
BANK: start = $4000, size = $4000, file = "";
SECHDR: start = $0000, size = $4, file = %O; # second load chunk
RAM: start = $8000, size = $3C20, file = %O; # $3C20: matches upper bound $BC1F
- TRAILER: start = $0000, size = $0006, file = %O;
}
SEGMENTS {
EXEHDR: load = BANK, type = ro;
NEXEHDR: load = HEADER, type = ro; # first load chunk
+ STARTUP: load = RAMLO, type = ro, define = yes;
LOWCODE: load = RAMLO, type = ro, define = yes, optional = yes;
INIT: load = RAMLO, type = ro, optional = yes;
CODE: load = RAMLO, type = ro, define = yes;
RODATA: load = RAM, type = ro, define = yes;
DATA: load = RAM, type = rw, define = yes;
BSS: load = RAM, type = bss, define = yes;
+ ZPSAVE: load = RAM, type = bss, define = yes;
ZEROPAGE: load = ZP, type = zp;
- AUTOSTRT: load = TRAILER, type = ro; # defines program entry point
+ AUTOSTRT: load = RAM, type = ro; # defines program entry point
}
FEATURES {
CONDES: segment = RODATA,
label = __DESTRUCTOR_TABLE__,
count = __DESTRUCTOR_COUNT__;
}
-SYMBOLS {
- __STACKSIZE__ = $800; # 2K stack
- __RESERVED_MEMORY__: value = $0, weak = yes;
-}
</verb></tscreen>
<p>
memory area isn't written to the output file. This way the contents of
the EXEHDR segment get discarded.
<p>
-The added NEXEHDR segment defines the correct EXE header. It puts only
-the CODE segment into load chunk #1 (RAMLO memory area).
+The newly added NEXEHDR segment defines the correct EXE header. It
+puts the STARTUP, LOWCODE, INIT, and CODE segments, which are the
+segments containing only code, into load chunk #1 (RAMLO memory area).
<p>
The header for the second load chunk comes from the new CHKHDR
-segment. It puts the RODATA and DATA segments into load chunk #2 (RAM
-memory area).
+segment. It puts the RODATA, DATA, BSS, and ZPSAVE segments into load
+chunk #2 (RAM memory area).
<p>
<p>
The contents of the new NEXEHDR and CHKHDR segments come from this
file (split.s):
<tscreen><verb>
- .import __LOWCODE_LOAD__, __BSS_LOAD__, __CODE_SIZE__
- .import __CODE_LOAD__, __DATA_LOAD__, __RODATA_LOAD__
-
- .segment "NEXEHDR"
- .word $FFFF ; EXE file magic number
- ; 1st load chunk
- .word __LOWCODE_LOAD__
- .word __CODE_LOAD__ + __CODE_SIZE__ - 1
-
- .segment "CHKHDR"
- ; 2nd load chunk (contains with AUTOSTRT in fact a 3rd load chunk)
- .word __RODATA_LOAD__
- .word __BSS_LOAD__ - 1
+ .import __CODE_LOAD__, __BSS_LOAD__, __CODE_SIZE__
+ .import __DATA_LOAD__, __RODATA_LOAD__, __STARTUP_LOAD__
+
+ .segment "NEXEHDR"
+ .word $FFFF
+ .word __STARTUP_LOAD__
+ .word __CODE_LOAD__ + __CODE_SIZE__ - 1
+
+ .segment "CHKHDR"
+ .word __RODATA_LOAD__
+ .word __BSS_LOAD__ - 1
</verb></tscreen>
<p>
Compile with
<sect2>Low data and high code example<p>
-Goal: Put RODATA and DATA into low memory and LOWCODE, INIT, CODE, BSS
-into high memory (split2.cfg):
+Goal: Put RODATA and DATA into low memory and STARTUP, LOWCODE, INIT,
+CODE, BSS, ZPSAVE into high memory (split2.cfg):
<tscreen><verb>
+SYMBOLS {
+ __STACKSIZE__ = $800; # 2K stack
+ __RESERVED_MEMORY__: value = $0000, weak = yes;
+}
+FEATURES {
+ STARTADDRESS: default = $2E00;
+}
MEMORY {
ZP: start = $82, size = $7E, type = rw, define = yes;
HEADER: start = $0000, size = $6, file = %O; # first load chunk
- RAMLO: start = $2E00, size = $1200, file = %O;
+ RAMLO: start = %S, size = $4000 - %S, file = %O;
BANK: start = $4000, size = $4000, file = "";
SECHDR: start = $0000, size = $4, file = %O; # second load chunk
RAM: start = $8000, size = $3C20, file = %O; # $3C20: matches upper bound $BC1F
- TRAILER: start = $0000, size = $0006, file = %O;
}
SEGMENTS {
EXEHDR: load = BANK, type = ro; # discarded old EXE header
DATA: load = RAMLO, type = rw, define = yes;
CHKHDR: load = SECHDR, type = ro; # second load chunk
- LOWCODE: load = RAM, type = ro, define = yes, optional = yes;
+ STARTUP: load = RAM, type = ro, define = yes;
INIT: load = RAM, type = ro, optional = yes;
CODE: load = RAM, type = ro, define = yes;
+ ZPSAVE: load = RAM, type = bss, define = yes;
BSS: load = RAM, type = bss, define = yes;
ZEROPAGE: load = ZP, type = zp;
- AUTOSTRT: load = TRAILER, type = ro; # defines program entry point
+ AUTOSTRT: load = RAM, type = ro; # defines program entry point
}
FEATURES {
CONDES: segment = RODATA,
label = __DESTRUCTOR_TABLE__,
count = __DESTRUCTOR_COUNT__;
}
-SYMBOLS {
- __STACKSIZE__ = $800; # 2K stack
- __RESERVED_MEMORY__: value = $0, weak = yes;
-}
</verb></tscreen>
New contents for NEXEHDR and CHKHDR are needed (split2.s):
<tscreen><verb>
- .import __LOWCODE_LOAD__, __BSS_LOAD__, __DATA_SIZE__
- .import __DATA_LOAD__, __RODATA_LOAD__
+ .import __STARTUP_LOAD__, __ZPSAVE_LOAD__, __DATA_SIZE__
+ .import __DATA_LOAD__, __RODATA_LOAD__
- .segment "NEXEHDR"
- .word $FFFF
- .word __RODATA_LOAD__
- .word __DATA_LOAD__ + __DATA_SIZE__ - 1
+ .segment "NEXEHDR"
+ .word $FFFF
+ .word __RODATA_LOAD__
+ .word __DATA_LOAD__ + __DATA_SIZE__ - 1
- .segment "CHKHDR"
- .word __LOWCODE_LOAD__
- .word __BSS_LOAD__ - 1
+ .segment "CHKHDR"
+ .word __STARTUP_LOAD__
+ .word __ZPSAVE_LOAD__ - 1
</verb></tscreen>
Compile with
projects / cc65 / commitdiff