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use crate::{Result, UsbError};
use crate::bus::{UsbBus, InterfaceNumber};
use crate::device;
use crate::endpoint::{Endpoint, EndpointDirection};
/// Standard descriptor types
#[allow(missing_docs)]
pub mod descriptor_type {
pub const DEVICE: u8 = 1;
pub const CONFIGURATION: u8 = 2;
pub const STRING: u8 = 3;
pub const INTERFACE: u8 = 4;
pub const ENDPOINT: u8 = 5;
}
/// String descriptor language IDs.
pub mod lang_id {
/// English (US)
///
/// Recommended for use as the first language ID for compatibility.
pub const ENGLISH_US: u16 = 0x0409;
}
/// A writer for USB descriptors.
pub struct DescriptorWriter<'a> {
buf: &'a mut [u8],
position: usize,
num_interfaces_mark: Option<usize>,
num_endpoints_mark: Option<usize>,
}
impl DescriptorWriter<'_> {
pub(crate) fn new(buf: &mut [u8]) -> DescriptorWriter<'_> {
DescriptorWriter {
buf,
position: 0,
num_interfaces_mark: None,
num_endpoints_mark: None,
}
}
/// Gets the current position in the buffer, i.e. the number of bytes written so far.
pub fn position(&self) -> usize {
self.position
}
/// Writes an arbitrary (usually class-specific) descriptor.
pub fn write(&mut self, descriptor_type: u8, descriptor: &[u8]) -> Result<()> {
let length = descriptor.len();
if self.position + 2 + length > self.buf.len() {
return Err(UsbError::BufferOverflow);
}
self.buf[self.position] = (length + 2) as u8;
self.buf[self.position + 1] = descriptor_type;
let start = self.position + 2;
self.buf[start..start + length].copy_from_slice(descriptor);
self.position = start + length;
Ok(())
}
pub(crate) fn device(&mut self, config: &device::Config) -> Result<()> {
self.write(
descriptor_type::DEVICE,
&[
0x00, 0x02, // bcdUSB
config.device_class, // bDeviceClass
config.device_sub_class, // bDeviceSubClass
config.device_protocol, // bDeviceProtocol
config.max_packet_size_0, // bMaxPacketSize0
config.vendor_id as u8, (config.vendor_id >> 8) as u8, // idVendor
config.product_id as u8, (config.product_id >> 8) as u8, // idProduct
config.device_release as u8, (config.device_release >> 8) as u8, // bcdDevice
config.manufacturer.map_or(0, |_| 1), // iManufacturer
config.product.map_or(0, |_| 2), // iProduct
config.serial_number.map_or(0, |_| 3), // iSerialNumber
1, // bNumConfigurations
])
}
pub(crate) fn configuration(&mut self, config: &device::Config) -> Result<()> {
self.num_interfaces_mark = Some(self.position + 4);
self.write(
descriptor_type::CONFIGURATION,
&[
0, 0, // wTotalLength
0, // bNumInterfaces
device::CONFIGURATION_VALUE, // bConfigurationValue
0, // iConfiguration
0x80
| if config.self_powered { 0x40 } else { 0x00 }
| if config.supports_remote_wakeup { 0x20 } else { 0x00 }, // bmAttributes
config.max_power // bMaxPower
])
}
pub(crate) fn end_class(&mut self) {
self.num_endpoints_mark = None;
}
pub(crate) fn end_configuration(&mut self) {
let position = self.position as u16;
self.buf[2..4].copy_from_slice(&position.to_le_bytes());
}
/// Writes a interface descriptor.
///
/// # Arguments
///
/// * `number` - Interface number previously allocated with
/// [`UsbBusAllocator::interface`](crate::bus::UsbBusAllocator::interface).
/// * `interface_class` - Class code assigned by USB.org. Use `0xff` for vendor-specific devices
/// that do not conform to any class.
/// * `interface_sub_class` - Sub-class code. Depends on class.
/// * `interface_protocol` - Protocol code. Depends on class and sub-class.
pub fn interface(&mut self, number: InterfaceNumber,
interface_class: u8, interface_sub_class: u8, interface_protocol: u8) -> Result<()>
{
self.buf[self.num_interfaces_mark.unwrap()] += 1;
self.num_endpoints_mark = Some(self.position + 4);
self.write(
descriptor_type::INTERFACE,
&[
number.into(), // bInterfaceNumber
device::DEFAULT_ALTERNATE_SETTING, // bAlternateSetting (how to even handle these...)
0, // bNumEndpoints
interface_class, // bInterfaceClass
interface_sub_class, // bInterfaceSubClass
interface_protocol, // bInterfaceProtocol
0, // iInterface
])?;
Ok(())
}
/// Writes an endpoint descriptor.
///
/// # Arguments
///
/// * `endpoint` - Endpoint previously allocated with
/// [`UsbBusAllocator`](crate::bus::UsbBusAllocator).
pub fn endpoint<'e, B: UsbBus, D: EndpointDirection>(&mut self, endpoint: &Endpoint<'e, B, D>)
-> Result<()>
{
self.buf[self.num_endpoints_mark.expect("missing interface descriptor")] += 1;
let mps = endpoint.max_packet_size();
self.write(
descriptor_type::ENDPOINT,
&[
endpoint.address().into(), // bEndpointAddress
endpoint.ep_type() as u8, // bmAttributes
mps as u8, (mps >> 8) as u8, // wMaxPacketSize
endpoint.interval(), // bInterval
])?;
Ok(())
}
/// Writes a string descriptor.
pub(crate) fn string(&mut self, string: &str) -> Result<()> {
let mut pos = self.position;
if pos + 2 > self.buf.len() {
return Err(UsbError::BufferOverflow);
}
self.buf[pos] = 0; // length placeholder
self.buf[pos + 1] = descriptor_type::STRING;
pos += 2;
for c in string.encode_utf16() {
if pos >= self.buf.len() {
return Err(UsbError::BufferOverflow);
}
self.buf[pos..pos + 2].copy_from_slice(&c.to_le_bytes());
pos += 2;
}
self.buf[self.position] = (pos - self.position) as u8;
self.position = pos;
Ok(())
}
}