mirror of
https://github.com/cc65/cc65.git
synced 2024-12-25 02:29:52 +00:00
81 lines
3.3 KiB
Plaintext
81 lines
3.3 KiB
Plaintext
LOADER.SYSTEM - an Apple][ ProDOS 8 loader for cc65 programs (Oliver Schmidt)
|
|
=============================================================================
|
|
|
|
|
|
Background
|
|
----------
|
|
|
|
Apple][ ProDOS 8 system programs (filetype SYS) are always loaded into memory
|
|
starting at location $2000. This poses the problem of how to make efficient
|
|
use of the memory in the range $0800-$2000. The usual approach of relocation
|
|
has two downsides:
|
|
- Relocating e.g. 30 kB from $2000-$9800 to $0800-$8000 takes a considerable
|
|
amount of time.
|
|
- Really large programs just don't fit into memory when loaded starting at
|
|
location $2000.
|
|
|
|
The relocation can be eliminated by loading the major part(s) of the program
|
|
from disk right to the final location by a rather small system program.
|
|
|
|
LOADER.SYSTEM is such a small program. In fact it's so small that it fits into
|
|
a single block in the ProDOS 8 file system making it a so-called seedling file,
|
|
which are loaded really fast. LOADER.SYSTEM can load cc65 programs into memory
|
|
anywhere in the range $0800-$BB00 (44,75 kB).
|
|
|
|
|
|
Usage
|
|
-----
|
|
|
|
Link the cc65 program to the start address $0803 (or any other address) and
|
|
store it as binary program (filetype BIN). This is in fact no different from
|
|
a binary program to be run by BASIC.SYSTEM's BRUN command in the usual way.
|
|
|
|
If however the cc65 program isn't run by BASIC.SYSTEM but is rather run by
|
|
LOADER.SYSTEM then it behaves like a system program which means:
|
|
- It uses memory up to the ProDOS 8 system global page located at $BF00.
|
|
- It supports the ProDOS 8 startup file mechanism (mapped to argv[1]).
|
|
- It quits to the ProDOS 8 dispatcher.
|
|
|
|
Obviously LOADER.SYSTEM has to be told which cc65 program to run. Unfortunately
|
|
the ProDOS 8 dispatcher has no notion of system program parameters so the usual
|
|
approach would have been to make LOADER.SYSTEM bring up yet another menu to
|
|
select the cc65 program to run.
|
|
|
|
But to allow to select the cc65 program directly from the ProDOS 8 dispatcher
|
|
anyway LOADER.SYSTEM detects the path to the cc65 program from its own path by
|
|
just removing the '.SYSTEM' from its name. So if you want to run the cc65
|
|
program MYPROGRAM you'll need a copy of LOADER.SYSTEM in the same directory
|
|
being renamed to MYPROGRAM.SYSTEM.
|
|
|
|
This means you will end up with a copy of LOADER.SYSTEM for every cc65 program
|
|
to be run by it. But as LOADER.SYSTEM is a ProDOS 8 seedling file using up only
|
|
a single block in the ProDOS 8 file system this should be no issue.
|
|
|
|
|
|
Build
|
|
-----
|
|
|
|
In case you want to build 'loader.system' from the source code yourself you can
|
|
do so using the following commands:
|
|
|
|
ca65 loader.s
|
|
ld65 -C loader.cfg -o loader.system loader.o
|
|
|
|
|
|
Installation
|
|
------------
|
|
|
|
The file 'loader.system' as generated by the cc65 linker with the command above
|
|
does NOT include the 4-byte address/length header that is generated for Apple][
|
|
programs by default. This is because ProDOS 8 system programs are always loaded
|
|
into memory starting at location $2000.
|
|
|
|
The recommended way to transfer 'loader.system' from your native file system to
|
|
a ProDOS 8 file system disk image is to use AppleCommander which is available at
|
|
http://applecommander.sourceforge.net/
|
|
|
|
If you want to put the file 'loader.system' onto a disk image 'mydisk.dsk' as
|
|
system program MYPROGRAM.SYSTEM you can do so using the following command:
|
|
|
|
java -jar ac.jar -p mydisk.dsk MYPROGRAM.SYSTEM sys < loader.system
|