USB DFU 1.1 Library

This crate provides a USB DFU 1.1 class implementation for OpenPRoT.

1. Overview

The USB DFU 1.1 protocol allows for firmware upgrades over USB. This implementation is designed for limited-memory devices and supports multiple alternate settings to address different memory regions (e.g., internal flash, external SPI flash, bootloader).

2. USB Descriptors

2.1 DFU Functional Descriptor

The DFU functional descriptor follows the USB DFU 1.1 specification.

Offset	Field	Size	Value	Description
0	bLength	1	0x09	Size of this descriptor in bytes.
1	bDescriptorType	1	0x21	DFU FUNCTIONAL descriptor type.
2	bmAttributes	1	0x07	bitCanDnload, bitCanUpload, bitManifestationTolerant.
3	wDetachTimeOut	2	0x0000	Time in ms to wait after DFU_DETACH.
5	wTransferSize	2	Configurable	Maximum number of bytes the device can accept per control-write.
7	bcdDFUVersion	2	0x0110	DFU specification release number in BCD.

2.2 Interface Descriptors

Multiple alternate settings are supported. Each altsetting typically represents a different memory partition.

Offset	Field	Size	Value	Description
0	bLength	1	0x09	Size of this descriptor in bytes.
1	bDescriptorType	1	0x04	INTERFACE descriptor type.
2	bInterfaceNumber	1	Variable	Number of this interface.
3	bAlternateSetting	1	Variable	Value used to select this alternate setting.
4	bNumEndpoints	1	0x00	No endpoints used (control only).
5	bInterfaceClass	1	0xFE	Application Specific Class.
6	bInterfaceSubClass	1	0x01	Device Firmware Upgrade.
7	bInterfaceProtocol	1	0x02	DFU Mode.
8	iInterface	1	Variable	Index of string descriptor describing this partition.

3. DFU Requests

The following DFU-specific requests are supported on the control endpoint (0):

Request	Code	Direction	Description
DFU_DETACH	0	Host to Device	Requests the device to leave its current mode and enter DFU mode.
DFU_DNLOAD	1	Host to Device	Data packets sent from the host to the device.
DFU_UPLOAD	2	Device to Host	Data packets sent from the device to the host.
DFU_GETSTATUS	3	Device to Host	Returns the current state and status of the device.
DFU_CLRSTATUS	4	Host to Device	Clears error status and returns to dfuIDLE.
DFU_GETSTATE	5	Device to Host	Returns the current state of the device.
DFU_ABORT	6	Host to Device	Aborts the current operation and returns to dfuIDLE.

4. State Machine

This implementation follows the DFU 1.1 state machine. For simplicity, all operations (flash erase/write) are performed synchronously within the DFU_DNLOAD and DFU_UPLOAD request handling, or immediately transition from SYNC to IDLE.

5. Application Interface (`DfuHandler`)

The application must provide an implementation of the DfuHandler trait.

pub trait DfuHandler {
    /// Handle a DNLOAD block.
    fn dnload(&mut self, alt: u8, block_num: u16, data: &[u8]) -> Result<(), DfuStatus>;
    /// Handle an UPLOAD block.
    fn upload(&mut self, alt: u8, block_num: u16, data: &mut [u8]) -> Result<usize, DfuStatus>;
    /// Perform manifestation.
    fn manifest(&mut self) -> Result<(), DfuStatus>;
    /// Abort current operation.
    fn abort(&mut self);
}