0.21.0

0.21.0

June 29, 2026

General

New MCUs and Boards

• Add HPMicro HPM6xxx support with HPM6750EVK2 board
• Add NXP RW61x (RW612, ChipIdea high-speed) support
• Add Artery AT32F45x series support
• Add STM32C5 series support
• Add Espressif ESP32-S31 (high-speed) support
• Add WCH CH582/CH583 (USBFS) support
• Add CH32V103 USB device support (combined-control USBFS) with CH32V103C8T6 Bluepill board
• Add FreeRTOS support for RP2040/RP2350
• New boards: nRF54LM20-DK, WeAct STM32H743, EK-TM4C1294XL, STM32H747-DISCO, NUCLEO-H533RE
• Migrate i.MX RT to the new mcux-devices-rt SDK package

Code Quality and Build

• Major refactor of dedicated hardware-FIFO (HWFIFO) handling: omit per-endpoint RAM buffers on ports with a dedicated hardware FIFO, add stride-aware FIFO access, and store raw bytes in tusb_fifo
• Reduce code size via control/descriptor and stream refactors, and remove snprintf usage
• Remove IAR toolchain support from the Make build; add IAR warning flags and resolve warnings in CMake
• Fix Zephyr build with nrfx v4, C++/-Werror=extra builds, and various -Wconversion warnings
• Update FatFS to R0.16
• Fix the fuzzing harness
• Various BSP fixes (STM32H5 UID read with ICACHE, STM32F411 Black Pill HSE, RT1011 data cache, Teensy)

Documentation

• Add a README for every example and build-doc tooling
• Add Sponsors section and FUNDING configuration
• Various README/doc fixes (FTDI host, STM32C071 Nucleo URL, Supported CPUs table)

API Changes

• Add is_isr parameter to dcd_edpt_xfer, dcd_edpt_xfer_fifo, usbd_edpt_xfer and usbd_edpt_xfer_fifo
• Remove the no-FIFO mode from the endpoint stream API
• Add tud_vendor_write_clear() to forcefully clear the TX buffer
• Add tud_midi_n_demux_stream_read() cable-aware MIDI stream read
• Add CFG_TUH_HID_SET_PROTOCOL_ON_ENUM host HID option
• Add CFG_TUSB_DEBUG_BREAKPOINT hook for TU_BREAKPOINT
• Add ThreadX OSAL support
• tud_task_ext() / tuh_task_ext() now limit the number of events processed per call
• Replace CFG_TUD_NET_ENDPOINT_SIZE with the descriptor-based endpoint size

Device Stack

USBD Core

• Refactor and validate device descriptor handling; move control transfer handling into usbd.c
• Use the EP0 buffer directly when large enough; clamp EP0 OUT data copy to the control buffer
• Fix stream write logic/racing without FIFO; fix zero wLength control request
• Fix ISO OUT endpoint failure on alt-setting MPS change

Audio

• Fix audiod_open with MIDI interfaces
• Fix big-endian bitfield guards for audio structs and endian-safe wValue/wIndex extraction in UAC2 examples

CDC

• Remove tud_cdc_configure
• Fix CDC echo test issue on i.MX RT and fast MCUs

HID

• Bound item size to remaining length in the report-descriptor parser
• Remove host enumeration assumption; add CFG_TUH_HID_SET_PROTOCOL_ON_ENUM

MIDI

• Add USB-MIDI 2.0 device and host class drivers
• Add cable-aware stream read tud_midi_n_demux_stream_read()
• Fix MIDI host issue

MSC

• Skip the command stage if the OUT endpoint is stalled
• Cap tud_msc_scsi_cb buffer size to the endpoint buffer size

MTP

• Fix transfer completion detection for exact-length packets; queue ZLP when needed
• Fix premature phase change after a short OUT transfer; fixes in add_string

Network (NCM)

• Fix NCM state on restart
• Support SetEthernetPacketFilter and SetNtbInputSize requests
• Add a weak callback for the initial link state

Video (UVC)

• Fix VC interface parsing when bNumEndpoints != 0
• Assert the usbd_edpt_iso_activate() result

DFU

• Fix the DFU functional descriptor version (1.0.1 → 1.1.0)

Printer

• Add the USB Printer device class driver

Vendor

• Omit the endpoint buffer for ports with a dedicated hardware FIFO

Host Stack

• Fully asynchronous host code: remove blocking delays from tuh_task_ext(), respect its timeout_ms, and avoid stalling one device while another enumerates
• Add an async control-transfer FIFO so queued control transfers are dispatched instead of dropped
• Hub enumeration reliability improvements; add MTT hub support
• Support full-speed host with a high-speed PHY (DWC2)
• Fix FTDI host multi-channel loop
• CDC host: use a local control buffer; fix cdch_open typo
• Big-endian host support for SETUP packet handling
• Use TUSB_ROLE_HOST in host stack initialization

Controller Driver (DCD & HCD)

DWC2

• Add dcd_configure for FIFO config and DWC2 deinit support
• Support full-speed host operation on a high-speed PHY
• Vbus sensing enhancement; do not modify FS PHY registers on HS PHY (ESP32-P4)
• Fix HCD TX FIFO full check, ISO IN endpoint disabled after incomplete transfer, and EP0 status completion before SETUP
• Submit SETUP on SETUP_DONE and handle v3.10a spurious RX_COMPLETE (STM32L476)
• HCD: correct HFIR for low-speed devices via internal FS PHY; fix split-IN NAK storm and UART starvation (STM32F723)

FSDEV (STM32 / CH32)

• Add FSDEV host (HCD) driver
• Refactor FSDEV; share the PMA errata delay helper between DCD/HCD with overridable timing
• Fix single-buffered isochronous endpoint cases, STM32U0 data stride, and PMA pointer advance on ring-buffer wrap
• Fix CH32V20x enumeration by enabling the D+ pull-up; work around CH32 EP0 premature OUT ACK
• Do not enable the unused USB wakeup EXTI IRQ (F1/F3/G4/L1)

MUSB

• Enhance driver: double packet, EP0 refactor, fix DATAEND race with EP0
• Fix ZLP IN transfer, RXRDY clearing, and defer EP0 SETUP during the DATA_IN/STATUS race

RP2040 / RP2350

• Refactor RP2 driver
• HCD rework: EPX for non-interrupt endpoints and ping-pong double buffering
• Fix RP2350 hard fault in unaligned memcpy to USB DPRAM
• Host: fix OUT-data control transfers sending DATA0 instead of DATA1

CH32 USBFS / USBHS (WCH)

• Fix dropped bulk OUT packets by re-arming the EP_RX_CTRL state (usbfs)
• Fix endpoint stall length index and clear-stall response (usbhs)
• Fix CH32V103 hard fault

RUSB2 / SAMx7x

• Fix RUSB2 FIFO write
• Refresh dcd_samx7x

New host controllers

• Add NXP IP3516 HCD (EHCI-like)
• Add MTT (multi-TT) hub support

nRF5x

• Request HFCLK in USB_EVT_READY to fix the post-SoftDevice deadlock

Testing

• Expand Hardware-in-the-Loop (HIL) coverage (MTP, audio, throughput; nanoch32v203, ch32v103, stm32u083nucleo, tm4c123x) and post pass/fail/skip HIL reports as PR comments
• Add MemBrowse code-size CI integration and size-difference reporting
• Add automated Claude Code PR review and bug-fix CI workflows
• Add hil, code-size, pvs, usbmon and build-doc developer skills

Contributors

Thanks to everyone who contributed to this release: @Alex-Schaefer, @alt-0191, @andrewleech, @armusin, @bdolgov, @BrentK-ADI, @ceedriic, @chenzhihong007, @dangfan, @DavidKorczynski, @dinsfire64, @dxbjavid, @embedded-ideas, @felhub, @gab-k, @gabChouin, @HakanL, @hathach, @HiFiPhile, @igi540, @IntegraSources, @kira-live, @LeZerb, @michael-membrowse, @michaelajax, @mickabrig7, @Milek7, @morse-cedricvandenbergh, @nminaylov, @non-bin, @Phozer, @remiberthoz, @renjieah, @rhgndf, @RobertDaleSmith, @roma-jam, @sauloverissimo, @sgrunza-at-BadgerMeter, @sidcha, @StefanOroel, @Tails86, @thamul, @tore-espressif, @UMRnInside, @ValentiWorkLearning, @verylowfreq, @wjklimek1, @YixingShen, @zhiqiang-ch, @zjzhang-cn.