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collapseos/recipes/sms/romasm/README.md
2019-07-25 14:24:18 -04:00

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