collapseos/recipes/sms/romasm/README.md

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

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.