code.rs

#[derive(Copy, Clone, Debug, Default, Deserialize, Serialize)]
#[repr(C, packed)]
pub struct USBDeviceDescriptor {
    pub b_length: u8,
    pub b_descriptor_type: USBDescriptor,
    pub bcd_usb: u16,
    pub b_device_class: u8,
    pub b_device_sub_class: u8,
    pub b_device_protocol: u8,
    pub b_max_packet_size: u8,
    pub id_vendor: u16,
    pub id_product: u16,
    pub bcd_device: u16,
    pub i_manufacturer: u8,
    pub i_product: u8,
    pub i_serial_number: u8,
    pub b_num_configurations: u8,
}

        // addr: 0x20007774
        let tmp: USBDeviceDescriptor = Default::default();
        // addr: 0x20007788
        let vol_descr = ::vcell::VolatileCell::new(tmp);
        self.control_req(
            0,
            0,
            BMRequestType::get_descr(),
            USBRequest::GetDescriptor,
            WValue::from((0, USBDescriptor::Device as u8)),
            0,
            Some(DataBuf::from(&vol_descr)),
        )?;

        let desc = vol_descr.get();
        info!(
            " -- len: {}, ver: {:04x}, bMaxPacketSize: {}, bNumConfigurations: {}",
            desc.b_length, desc.bcd_usb, desc.b_max_packet_size, desc.b_num_configurations
        );

error

warning: borrow of packed field is unsafe and requires unsafe function or block (error E0133)
   --> src/lib.rs:418:28
    |
418 |             desc.b_length, desc.bcd_usb, desc.b_max_packet_size, desc.b_num_configurations
    |                            ^^^^^^^^^^^^
    |
    = note: #[warn(safe_packed_borrows)] on by default
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #46043 <https://github.com/rust-lang/rust/issues/46043>
    = note: fields of packed structs might be misaligned: dereferencing a misaligned pointer or even just creating a misaligned reference is undefined behavior