Example of usage with STM32

[snorkman88]

Describe the solution you'd like
A clear and concise description of what you want to happen.

I am in the process of building my own control surface and would like to use this crate an an STM32F4 Blackpill.
Do you have an example that I can use as a starting point?

[sourcebox]

Which HAL are you using for the STM32F4?

[snorkman88]

Hi there, I am using v1.0.0 for all my projects.

[sourcebox]

I think you mean the embedded-hal crate, but that's not what I was asking. There are several options for HAL implementations targeting an STM32F4 like:

• stm32f4xx-hal
• stm32-hal
• embassy-stm32

Each of these HALs have their own way to setup things and also contain example code how to use USB in general. The first two options can be used with this crate, embassy however has it's own implementation of a MIDI device class.

[snorkman88]

Oh my bad, sorry!.
I am using stm32f4xx-hal.

[sourcebox]

Here's some code based on the README using a modification of the serial example.

You have to activate the features stm32f411, otg-fs and usb_fs for the stm32f4xx-hal crate, of course and also adapt the clock configuration.

//! USB MIDI example using polling in a busy loop.
//! Target board: any STM32F4 with a OTG FS peripheral and a 25MHz HSE crystal
#![no_std]
#![no_main]

use panic_halt as _;

use cortex_m_rt::entry;
use stm32f4xx_hal::otg_fs::{UsbBus, USB};
use stm32f4xx_hal::{pac, prelude::*};
use usb_device::prelude::*;
use usbd_midi::{
    data::{
        midi::{channel::Channel, message::Message, notes::Note},
        usb_midi::midi_packet_reader::MidiPacketBufferReader,
    },
    midi_device::MidiClass,
};

static mut EP_MEMORY: [u32; 1024] = [0; 1024];

#[entry]
fn main() -> ! {
    let dp = pac::Peripherals::take().unwrap();

    let rcc = dp.RCC.constrain();

    let clocks = rcc
        .cfgr
        .use_hse(25.MHz())
        .sysclk(48.MHz())
        .require_pll48clk()
        .freeze();

    let gpioa = dp.GPIOA.split();

    let usb = USB::new(
        (dp.OTG_FS_GLOBAL, dp.OTG_FS_DEVICE, dp.OTG_FS_PWRCLK),
        (gpioa.pa11, gpioa.pa12),
        &clocks,
    );

    let usb_bus = UsbBus::new(usb, unsafe { &mut EP_MEMORY });

    // Create a MIDI class with 1 input and 1 output jack.
    let mut midi = MidiClass::new(&usb_bus, 1, 1).unwrap();

    let mut usb_dev = UsbDeviceBuilder::new(&usb_bus, UsbVidPid(0x16c0, 0x5e4))
        .device_class(0)
        .device_sub_class(0)
        .strings(&[StringDescriptors::default()
            .manufacturer("Fake Company")
            .product("Product")
            .serial_number("TEST")])
        .unwrap()
        .build();

    loop {
        if !usb_dev.poll(&mut [&mut midi]) {
            continue;
        }

        let mut buffer = [0; 64];

        if let Ok(size) = midi.read(&mut buffer) {
            let buffer_reader = MidiPacketBufferReader::new(&buffer, size);
            for packet in buffer_reader.into_iter() {
                if let Ok(packet) = packet {
                    match packet.message {
                        Message::NoteOn(Channel::Channel1, Note::C2, ..) => {
                            // Do something.
                        }
                        Message::NoteOff(Channel::Channel1, Note::C2, ..) => {
                            // Do something.
                        }
                        _ => {}
                    }
                }
            }
        }
    }
}

[snorkman88]

@sourcebox Thanks a lot!!!

[snorkman88]

@sourcebox I have tried this code with a minor change to punt DP and DM pins into altenate mode (AF10). The code looks like this:

        // Configure the button pin as input and obtain handle
        // On the Blackpill STM32F411CEU6 there is a button connected to pin PA0
        // 6) Promote the GPIOA PAC struct
        let gpioa: gpio::gpioa::Parts = dp.GPIOA.split();

        // Configure USB pins to be of type alternate function 10 (AF10)
        let usb_dm: gpio::Pin<'A', 11, gpio::Alternate<10>>  = gpioa.pa11.into_alternate();
        let usb_dp: gpio::Pin<'A', 12, gpio::Alternate<10>> = gpioa.pa12.into_alternate();

        // 7) Configure USB peripheral
        let usb = USB::new(
            (dp.OTG_FS_GLOBAL, dp.OTG_FS_DEVICE, dp.OTG_FS_PWRCLK),
            (usb_dm, usb_dp),
            &clocks,
        );
        let usb_bus = UsbBus::new(usb, unsafe { &mut EP_MEMORY });

        // Create a MIDI class with 1 input and 1 output jack.
        let mut midi = MidiClass::new(&usb_bus, 1, 1).unwrap();
        let mut usb_dev = UsbDeviceBuilder::new(&usb_bus, UsbVidPid(0x16c0, 0x5e4))
            .device_class(0)
            .device_sub_class(0)
            .strings(&[StringDescriptors::default()
                .manufacturer("Fake Company")
                .product("Product")
                .serial_number("TEST")])
            .unwrap()
            .build();

        defmt::info!("Before entering loop");
        loop {
            if !usb_dev.poll(&mut [&mut midi]) {
                continue;
            }
            defmt::info!("Left USB Poll");
            let mut buffer = [0; 64];
            let payload = UsbMidiEventPacket::from_midi(
                CableNumber::Cable0,
                Message::NoteOn(
                    Channel::Channel1,                            // Channel
                    Note::C3,                                     // Note
                    U7::from(Note::try_from(127 as u8).unwrap()), // Velocity
                ),
            );
            let result = midi.send_message(payload);
            delay.delay_ms(1000_u32);
        }

this code compiles fine but it hangs when UsbDeviceBuilder::new(...) is invoked. Did I miss anything?
Thanks in advance for any help.

[sourcebox]

Unfortunately, I don't have the appropriate hardware to run this. Did you activate the control-buffer-256 feature on the usb-device crate? Because not doing so can lead to crashes when the config descriptor gets too large and with USB MIDI, that can happen quite easily.

[snorkman88]

Unfortunately, I don't have the appropriate hardware to run this. Did you activate the control-buffer-256 feature on the usb-device crate? Because not doing so can lead to crashes when the config descriptor gets too large and with USB MIDI, that can happen quite easily.

I have just re-tried enabling control-buffer-256 and the behaviour is the same. Any other suggestion?

[sourcebox]

I have just re-tried enabling control-buffer-256 and the behaviour is the same. Any other suggestion?

If the code stalls inside UsbDeviceBuilder::new(), there's a good chance that the problem is not related to this crate but usb-device in general.

Some suggestions:

• Try to use the current git version of usb-device via [patch.crates-io]. You need some changes in your code because of different control buffer management.
• Try to run another USB example from the HAL like the {serial-example](https://github.com/stm32-rs/stm32f4xx-hal/blob/master/examples/usb-serial-poll.rs) and check if it also crashes.
• There's a room on Matrix where the maintainers of usb-device are also present and maybe someone has a compatible board to run your code.
• There's also Discord-Server where someone else can help.

Overall, this is the kind of issue that has to be checked on the target hardware with a JTAG debug probe connected. Using that, you can single step the code up to the point where it hangs or crashes.

[snorkman88]

Thanks again for the suggestions, I will keep you posted if I make it work.

[snorkman88]

• Try to run another USB example from the HAL like the {serial-example](https://github.com/stm32-rs/stm32f4xx-hal/blob/master/examples/usb-serial-poll.rs) and check if it also crashes.

I have jsut tested and I can confirm this works.

[sourcebox]

I have jsut tested and I can confirm this works.

Ok, good to know. But the serial device has a much simpler descriptor, so it's not sure whether usbd-midi is doing something wrong internally.

[sourcebox]

There was some issue with STM32F4 devices mentioned on the tracker a while ago, but this can be unrelated:

rust-embedded-community/usb-device#112 (comment)

[snorkman88]

Aghh!! I have just noticed I missed sth very basic: I forgot to enable the PLL!
It lists for a short period of time now :-) but with the following line, afterwards it disappears.

I suspect this is due to me running macOS.