Protocol Design on Michael-F-Bryan

Wiring Up Communication

Thu, 10 Oct 2019 22:58:00 +0800

As we mentioned in the last AiMC post , the next task is to wire up communications between the simulator’s backend and frontend.

As a general rule, our frontend will have two communication regimes:

When something happens (e.g. a button is pressed or a job starts sending), the frontend will send a batch of messages to the backend and interpret the response
The frontend will continually poll the backend’s state in the background (e.g. at 10Hz)

As it is, the Browser in our WASM code already provides a method for sending data to the frontend (Browser::send_data() ) and receiving data from the frontend (App::on_data_received() ) so we shouldn’t need to write any Rust code.

The Communications System: Part 2

Sun, 08 Sep 2019 01:20:00 +0800

Now we have a mechanism for transferring bytes from the frontend to the simulator and back again, we need to translate those bytes into higher-level messages. Luckily each [anpp::Packet] contains an ID field that is designed specifically for this purpose.

That lets us do something like this:

// (not real code)

enum Message<'a> {
 Ping,
 StatusCheck,
 ProgramChunk {
 chunk_number: usize,
 body: &'a [u8],
 },
 ...
}

struct UnknownMessageError;

fn parse_packet<'a>(pkt: &'a Packet) -> Result<Message<'a>, UnknownMessageError> {
 match pkt.id() {
 0 => Ok(Message::Ping),
 1 => Ok(Message::StatusCheck),
 2 => Ok(...),
 _ => Err(UnknownMessageError),
 }
}

The top-level App can handle messages by routing them to the appropriate system and invoking a message handler.

The Communications System: Part 1

Fri, 06 Sep 2019 23:00:00 +0800

Prelude Link to heading

The Communications system is arguably one of the most important parts of our simulator. After all, it’s kinda hard to debug a program when you can’t ask it why something isn’t working.

The user will interact with our simulated motion controller via a single Serial Port, which we’ll be modelling as a simple thing which sends and receives bytes. Serial ports are a fairly old technology, and have several drawbacks compared to the Ethernet and TCP protocols that most programmers are familiar with.