mirror of https://github.com/hsoft/collapseos.git
62 lines
1.6 KiB
Markdown
62 lines
1.6 KiB
Markdown
# zasm and ed from ROM
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SMS' RAM is much tighter than in the RC2014, which makes the idea of loading
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apps like zasm and ed in memory before using it a bit wasteful. In this recipe,
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we'll include zasm and ed code directly in the kernel and expose them as shell
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commands.
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Moreover, we'll carve ourselves a little 1K memory map to put a filesystem in
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there. This will give us a nice little system that can edit small source files
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compile them and run them.
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## Gathering parts
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* A SMS that can run Collapse OS.
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* A [PS/2 keyboard adapter](../kbd/README.md)
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## Build
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There's nothing special with building this recipe. Like the base recipe, run
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`make` then copy `os.sms` to your destination medium.
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If you look at the makefile, however, you'll see that we use a new trick here:
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we embed "apps" binaries directly in our ROM so that we don't have to load them
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in memory.
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## Usage
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Alright, here's what we'll do: we'll author a source file, assemble it and run
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it, *all* on your SMS! Commands:
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Collapse OS
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> fnew 1 src
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> ed src
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: 1i
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.org 0xc200
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: 1a
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ld hl, sFoo
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: 2a
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call 0x3f
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: 3a
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xor a
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: 4a
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ret
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: 5a
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sFoo: .db "foo", 0
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: w
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> fnew 1 dest
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> fopn 0 src
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> fopn 1 dest
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> zasm 1 2
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First pass
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Second pass
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> dest
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foo>
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Awesome right? Some precisions:
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* Our glue code specifies a `USER_RAMSTART` of `0xc200`. This is where
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`dest` is loaded by the `pgm` shell hook.
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* `0x3f` is the offset of `printstr` in the jump table of our glue code.
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* `xor a` is for the command to report as successful to the shell.
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