PC to USB Device comms example

Cargo.toml

[package]
name = "pedalrs_gui"
version = "0.1.0"
authors = ["Will Hart <hart.wl@gmail.com>"]
edition = "2021"
rust-version = "1.56"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[lib]
crate-type = ["cdylib", "rlib"]

[dependencies]
rusb = "0.9.0"

[profile.release]
opt-level = 2 # fast and small wasm

main.rs

use crate::usb_device;

static VID: u16 = 0x16c0;
static PID: u16 = 0x27dd;

pub fn main() {
  usb_device::send_message(VID, PID, 0x08).ok();
}

usb_device.rs

use std::time::Duration;

use rusb::{
    Context, Device, DeviceDescriptor, DeviceHandle, Direction, Result, TransferType, UsbContext,
};

#[derive(Debug)]
struct Endpoint {
    config: u8,
    iface: u8,
    setting: u8,
    address: u8,
}

pub fn send_message(vid: u16, pid: u16, command: u8) -> Result<bool> {
    match Context::new() {
        Ok(mut context) => match open_device(&mut context, vid, pid) {
            Some((mut device, device_desc, mut handle)) => {
                write_device(&mut device, &device_desc, &mut handle, command)
            }
            None => {
                println!("could not find device {:04x}:{:04x}", vid, pid);
                Ok(false)
            }
        },
        Err(e) => panic!("could not initialize libusb: {}", e),
    }
}

fn open_device<T: UsbContext>(
    context: &mut T,
    vid: u16,
    pid: u16,
) -> Option<(Device<T>, DeviceDescriptor, DeviceHandle<T>)> {
    let devices = match context.devices() {
        Ok(d) => d,
        Err(_) => return None,
    };

    for device in devices.iter() {
        let device_desc = match device.device_descriptor() {
            Ok(d) => d,
            Err(_) => continue,
        };

        if device_desc.vendor_id() == vid && device_desc.product_id() == pid {
            match device.open() {
                Ok(handle) => return Some((device, device_desc, handle)),
                Err(_) => continue,
            }
        }
    }

    None
}

fn write_device<T: UsbContext>(
    device: &mut Device<T>,
    device_desc: &DeviceDescriptor,
    handle: &mut DeviceHandle<T>,
    command: u8,
) -> Result<bool> {
    handle.reset()?;

    let timeout = Duration::from_secs(1);
    let languages = handle.read_languages(timeout)?;

    println!("Active configuration: {}", handle.active_configuration()?);
    println!("Languages: {:?}", languages);

    if languages.len() > 0 {
        let language = languages[0];

        println!(
            "Manufacturer: {:?}",
            handle
                .read_manufacturer_string(language, device_desc, timeout)
                .ok()
        );
        println!(
            "Product: {:?}",
            handle
                .read_product_string(language, device_desc, timeout)
                .ok()
        );
        println!(
            "Serial Number: {:?}",
            handle
                .read_serial_number_string(language, device_desc, timeout)
                .ok()
        );
    }

    match find_writable_endpoint(device, device_desc, TransferType::Interrupt) {
        Some(endpoint) => {
            println!(" - Found interrupt mode on endpoint");
            write_endpoint(handle, endpoint, TransferType::Interrupt, command);
            return Ok(true);
        }
        None => println!(" - No interrupt mode on endpoint"),
    }

    match find_writable_endpoint(device, device_desc, TransferType::Bulk) {
        Some(endpoint) => {
            println!(" - Found bulk mode on endpoint");
            write_endpoint(handle, endpoint, TransferType::Bulk, command);
            return Ok(true);
        }
        None => println!(" - No bulk mode on endpoint"),
    }

    Ok(false)
}

fn find_writable_endpoint<T: UsbContext>(
    device: &mut Device<T>,
    device_desc: &DeviceDescriptor,
    transfer_type: TransferType,
) -> Option<Endpoint> {
    for n in 0..device_desc.num_configurations() {
        let config_desc = match device.config_descriptor(n) {
            Ok(c) => c,
            Err(_) => continue,
        };

        for (interface_number, interface) in config_desc.interfaces().enumerate() {
            for interface_desc in interface.descriptors() {
                for (endpoint_number, endpoint_desc) in
                    interface_desc.endpoint_descriptors().enumerate()
                {
                    if endpoint_desc.direction() == Direction::Out
                        && endpoint_desc.transfer_type() == transfer_type
                    {
                        println!(
                            "Found writable endpoint {}:{} at address {} for device {}",
                            interface_number,
                            endpoint_number,
                            endpoint_desc.address(),
                            device.address()
                        );
                        return Some(Endpoint {
                            config: config_desc.number(),
                            iface: interface_desc.interface_number(),
                            setting: interface_desc.setting_number(),
                            address: endpoint_desc.address(),
                        });
                    }
                }
            }
        }
    }

    None
}

fn write_endpoint<T: UsbContext>(
    handle: &mut DeviceHandle<T>,
    endpoint: Endpoint,
    transfer_type: TransferType,
    command: u8,
) {
    println!("Writing to endpoint: {:?}", endpoint);

    let has_kernel_driver = match handle.kernel_driver_active(endpoint.iface) {
        Ok(true) => {
            handle.detach_kernel_driver(endpoint.iface).ok();
            true
        }
        _ => false,
    };

    println!(" - kernel driver? {}", has_kernel_driver);

    match configure_endpoint(handle, &endpoint) {
        Ok(_) => {
            let timeout = Duration::from_secs(1);
            println!("Handle state {:?}", handle);

            match transfer_type {
                TransferType::Interrupt => {
                    match handle.write_interrupt(endpoint.address, &mut [0x00; 4], timeout) {
                        Ok(len) => {
                            println!(" - wrote: {} bytes", len);
                        }
                        Err(err) => {
                            println!("could not write to endpoint: {}", err);
                        }
                    }
                }
                TransferType::Bulk => {
                    match handle.write_bulk(endpoint.address, &mut [0x01, command], timeout) {
                        Ok(len) => {
                            println!(" - wrote {:?} bytes", len);
                        }
                        Err(err) => println!("could not write to endpoint: {}", err),
                    }
                }
                _ => (),
            }
        }
        Err(err) => println!("could not configure endpoint: {}", err),
    }

    if has_kernel_driver {
        handle.attach_kernel_driver(endpoint.iface).ok();
    }
}

fn configure_endpoint<T: UsbContext>(
    handle: &mut DeviceHandle<T>,
    endpoint: &Endpoint,
) -> Result<()> {
    println!(
        "Configuring for sending, and claiming the interface. {:?}",
        endpoint
    );
    handle.set_active_configuration(endpoint.config)?;
    handle.claim_interface(endpoint.iface)?;
    handle.set_alternate_setting(endpoint.iface, endpoint.setting)?;
    Ok(())
}