85 lines
3.4 KiB
Text
85 lines
3.4 KiB
Text
Apple][ ProDOS 8 system program for loading binary programs (Oliver Schmidt)
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============================================================================
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Background
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----------
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The ordinary way to run a binary program using ProDOS 8 is to load BASIC.SYSTEM
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first and enter then from the BASIC prompt 'BRUN MYPROGRAM' or '- MYPROGRAM'.
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Using LOADER.SYSTEM instead to run a binary program has four advantages:
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1. The binary program can be selected directly from the ProDOS 8 dispatcher.
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2. The size of BASIC.SYSTEM is 21 blocks while the size of LOADER.SYSTEM is
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only 1 block. The benefits are:
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- Running a binary program with LOADER.SYSTEM is faster.
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- If the only use of BASIC.SYSTEM is to run binary programs it can be removed
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altogether thus freeing up precious floppy disk space.
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3. BASIC.SYSTEM can load binary programs into the range $0800-$9600 (35,5 kB)
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while LOADER.SYSTEM can load much larger binary programs into the range
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$0800-$BB00 (44,75 kB).
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4. If a binary program needs to reclaim the memory used by BASIC.SYSTEM it has
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to update the system bit map after being loaded and on exit it must call the
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ProDOS 8 dispatcher itself. But when run by LOADER.SYSTEM the binary program
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automatically has access to the range $0800-$BF00 (45,75 kB) just by checking
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HIMEM. On exit the binary program simply jumps to DOSWARM or DOSCOLD as usual
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which are set up by LOADER.SYSTEM to call the ProDOS 8 dispatcher (or reboot
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the computer - see below).
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Usage
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-----
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Obviously LOADER.SYSTEM has to be told which binary program to run. As the
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ProDOS 8 dispatcher has no notion of system program parameters the ordinary
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approach would have been to make LOADER.SYSTEM bring up yet another menu to
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select the binary program to run.
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But to allow to select the binary program directly from the ProDOS 8 dispatcher
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anyway LOADER.SYSTEM detects the path to the binary program from its own path
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by just removing the '.SYSTEM' from its name. So if you want to run the binary
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program MYPROGRAM you'll need a copy of LOADER.SYSTEM in the same directory
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being renamed to MYPROGRAM.SYSTEM.
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This means you'll end up with a copy of LOADER.SYSTEM for every binary program
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you intend to run it. But as LOADER.SYSTEM is a seedling file using up only a
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single block in the ProDOS 8 file system this should be no issue.
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Build
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-----
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In case you want to build 'loader.system' from the source code yourself you can
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do so using the following commands:
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ca65 loader.s
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ld65 -C loader.cfg -o loader.system loader.o
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If you want LOADER.SYSTEM to reboot the computer on exit of the binary program
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instead of calling the ProDOS 8 dispatcher then use the following commands:
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ca65 -D REBOOT loader.s
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ld65 -C loader.cfg -o loader.system loader.o
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Installation
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------------
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The file 'loader.system' as generated by the cc65 linker does NOT have a 4-byte
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address/length header as it is generated for ordinary Apple][ binaries. This is
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because the start address for ProDOS 8 system programs is fixed to $2000.
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The recommended way to transfer 'loader.system' from your native file system to
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a ProDOS 8 file system disk image is to use AppleCommander which is available at
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http://applecommander.sourceforge.net/
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If you want to put the file 'loader.system' onto a disk image 'mydisk.dsk' as
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system program MYPROGRAM.SYSTEM you can do so using the following command:
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java -jar ac.jar -p mydisk.dsk MYPROGRAM.SYSTEM sys < loader.system
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