mirror of
https://github.com/hsoft/collapseos.git
synced 2024-09-07 14:48:46 +10:00
128 lines
3.9 KiB
Markdown
128 lines
3.9 KiB
Markdown
# Load code in RAM and run it
|
|
|
|
Collapse OS likely runs from ROM code. If you need to fiddle with your machine
|
|
more deeply, you will want to send arbitrary code to it and run it. You can do
|
|
so with the shell's `poke` and `usr` commands.
|
|
|
|
For example, let's say that you want to run this simple code that you have
|
|
sitting on your "modern" machine and want to execute on your running Collapse OS
|
|
machine:
|
|
|
|
ld a, (0xa100)
|
|
inc a
|
|
ld (0xa100), a
|
|
ret
|
|
|
|
(we must always return at the end of code that we call with `usr`). This will
|
|
increase a number at memory address `0xa100`. First, compile it:
|
|
|
|
zasm < tosend.asm > tosend.bin
|
|
|
|
Now, we'll send that code to address `0xa000`:
|
|
|
|
> m=0xa000
|
|
> while m<0xa008 getc:poke m a:m=m+1
|
|
(resulting binary is 8 bytes long)
|
|
|
|
Now, at this point, it's a bit delicate. To pipe your binary to your serial
|
|
connection, you have to close `screen` with CTRL+A then `:quit` to free your
|
|
tty device. Then, you can run:
|
|
|
|
cat tosend.bin > /dev/ttyUSB0 (or whatever is your device)
|
|
|
|
You can then re-open your connection with screen. You'll have a blank screen,
|
|
but if the number of characters sent corresponds to what you gave `poke`, then
|
|
Collapse OS will be waiting for a new command. Go ahead, verify that the
|
|
transfer was successful with:
|
|
|
|
> peek 0a000
|
|
> puth a
|
|
3A
|
|
> peek 0a007
|
|
> puth a
|
|
C9
|
|
|
|
Good! Now, we can try to run it. Before we run it, let's peek at the value at
|
|
`0xa100` (being RAM, it's random):
|
|
|
|
> peek 0xa100
|
|
> puth a
|
|
61
|
|
|
|
So, we'll expect this to become `62` after we run the code. Let's go:
|
|
|
|
> usr 0xa100
|
|
> peek 0xa100
|
|
> puth a
|
|
62
|
|
|
|
Success!
|
|
|
|
## The upload tool
|
|
|
|
The serial connection is not always 100% reliable and a bad byte can slip in
|
|
when you push your code and that's not fun when you try to debug your code (is
|
|
this bad behavior caused by my logic or by a bad serial upload?). Moreover,
|
|
sending contents manually can be a hassle.
|
|
|
|
To this end, there is a `upload` file in `tools/` (run `make` to build it) that
|
|
takes care of loading the file and verify the contents. So, instead of doing
|
|
`getc` followed by `poke` followed by your `cat` above, you would have done:
|
|
|
|
./upload /dev/ttyUSB0 a000 tosend.bin
|
|
|
|
This clears your basic listing and then types in a basic algorithm to receive
|
|
and echo and pre-defined number of bytes. The `upload` tool then sends and read
|
|
each byte, verifying that they're the same. Very handy.
|
|
|
|
## Labels in RAM code
|
|
|
|
If your code contains any label, make sure that you add a `.org` directive at
|
|
the beginning of your code with the address you're planning on uploading your
|
|
code to. Otherwise, those labels are going to point to wrong addresses.
|
|
|
|
## Calling ROM code
|
|
|
|
The ROM you run Collapse OS on already has quite a bit of code in it, some of
|
|
it could be useful to programs you run from RAM.
|
|
|
|
If you know exactly where a routine lives in the ROM, you can `call` the address
|
|
directly, no problem. However, getting this information is tedious work and is
|
|
likely to change whenever you change the kernel code.
|
|
|
|
A good approach is to define yourself a jump table that you put in your glue
|
|
code. A good place for this is in the `0x03` to `0x37` range, which is empty
|
|
anyways (unless you set yourself up with some `rst` jumps) and is needed to
|
|
have a proper interrupt hook at `0x38`. For example, your glue code could look
|
|
like (important fact: `jp <addr>` uses 3 bytes):
|
|
|
|
jp init
|
|
; JUMP TABLE
|
|
jp printstr
|
|
jp aciaPutC
|
|
|
|
.fill 0x38-$
|
|
jp aciaInt
|
|
|
|
init:
|
|
[...]
|
|
|
|
It then becomes easy to build yourself a predictable and stable jump header,
|
|
something you could call `jumptable.inc`:
|
|
|
|
.equ JUMP_PRINTSTR 0x03
|
|
.equ JUMP_ACIAPUTC 0x06
|
|
|
|
You can then include that file in your "user" code, like this:
|
|
|
|
#include "jumptable.inc"
|
|
.org 0xa000
|
|
ld hl, label
|
|
call JUMP_PRINTSTR
|
|
ret
|
|
|
|
label: .db "Hello World!", 0
|
|
|
|
If you load that code at `0xa000` and call it, it will print "Hello World!" by
|
|
using the `printstr` routine from `core.asm`.
|