A framework to build fast and reliable Modbus-powered applications.
Cargo crate: https://crates.io/crates/rmodbus
rmodbus is not a yet another Modbus server. rmodbus is a set of tools to quickly build Modbus-powered applications.
rmodbus is transport and protocol independent
rmodbus is platform independent (no_std is fully supported!)
can be easily used in blocking and async (non-blocking) applications
tuned for speed and reliability
provides a set of tools to easily work with Modbus context
supports server frame processing for Modbus TCP/UDP and RTU
server context can be easily, managed, imported and exported
Yes, there's no server included. You build the server by your own. You choose protocol, technology and everything else. rmodbus just process frames and works with Modbus context.
Here's an example of a simple TCP blocking server:
```rust use std::io::{Read, Write}; use std::net::TcpListener; use std::thread;
use rmodbus::server::{ModbusFrame, ModbusProto, process_frame};
pub fn tcpserver(unit: u8, listen: &str) { let listener = TcpListener::bind(listen).unwrap(); println!("listening started, ready to accept"); for stream in listener.incoming() { thread::spawn(move || { println!("client connected"); let mut stream = stream.unwrap(); loop { let mut buf: ModbusFrame = [0; 256]; let mut response = Vec::new(); // for nostd use FixedVec with alloc [u8;256] if stream.read(&mut buf).unwrapor(0) == 0 { return; } if processframe(unit, &buf, ModbusProto::TcpUdp, &mut response).iserr() { println!("server error"); return; } println!("{:x?}", response.asslice()); if !response.isempty() { if stream.write(response.asslice()).is_err() { return; } } } }); } } ```
There are also examples for Serial-RTU and UDP in examples folder (if you're reading this text somewhere else, visit rmodbus project repository.
The rule is simple: one standard Modbus context per application. 10k+10k 16-bit registers and 10k+10k coils are usually more than enough. This takes about 43Kbytes of RAM, but if you need to reduce context size, download library source and change CONTEXT_SIZE constant in "context.rs".
rmodbus server context is thread-safe, easy to use and has a lot of functions.
The context is created automatically, as soon as the library is imported. No additional action is required.
Every time Modbus context is accessed, a context mutex must be locked. This slows down a performance, but guarantees that the context always has valid data after bulk-sets or after 32-bit data types were written. So make sure your application locks context only when required and only for a short period time.
There are two groups of context functions:
High-level API: simple functions like coil_get automatically lock the context but do this every time when called. Use this for testing or if the speed is not important.
Advanced way is to use low-level API, lock the context manually and then call proper functions, like set, set_f32 etc.
Take a look at simple PLC example:
```rust use rmodbus::server::context; use std::fs::File; use std::io::prelude::*;
fn looping() { loop { // READ WORK MODES ETC let mut ctx = context::CONTEXT.lock().unwrap(); let param1 = context::get(1000, &ctx.holdings).unwrap(); let _param2 = context::getf32(1100, &ctx.holdings).unwrap(); // ieee754 f32 let param3 = context::getu32(1200, &ctx.holdings).unwrap(); // u32 let cmd = context::get(1500, &ctx.holdings).unwrap(); context::set(1500, 0, &mut ctx.holdings).unwrap(); if cmd != 0 { println!("got command code {}", cmd); match cmd { 1 => { println!("saving memory context"); //let _ = savelocked("/tmp/plc1.dat", &ctx).maperr(|| { //eprintln!("unable to save context!"); //}); } _ => println!("command not implemented"), } } drop(ctx); // ============================================== // DO SOME JOB // .......... // WRITE RESULTS let mut ctx = context::CONTEXT.lock().unwrap(); context::set(0, true, &mut ctx.coils).unwrap(); context::setbulk(10, &(vec![10, 20]), &mut ctx.holdings).unwrap(); context::set_f32(20, 935.77, &mut ctx.inputs).unwrap(); } } ```
To let the above program communicate with outer world, Modbus server must be up and running in the separate thread, asynchronously or whatever is preferred.
rmodbus supports working in no_std mode. Most of the library code is written the way to support both std and no_std.
I found no way to publish 2 libraries from the single crate with cargo. To switch to no_std:
clone https://github.com/alttch/rmodbus
execute "make switch-nostd"
put the local path to rmodbus library in your Cargo.toml
When switched, library loads traits for different types, so if something's wrong, the project will just fail to build.
To perform context bulk gets and obtain responses from Modbus frame processing, use FixedVec instead of std::vec::Vec
In the no_std mode, rmodbus context is protected with spin Mutex instead of std::sync::mutex. Note that spin MutexGuard doesn't require unwrap() after locking.
Single-threaded applications can gain up to +60-100% speed boost by removing Modbus context mutex. This can be performed by running "make switch-nostd-single" and replacing mutex with a fake one. For the compatibility, the context still need to be "unlocked", however the fake mutex does this instantly and without any CPU overhead.
Planned.