imxrtnsy

Bare-metal USB proxy firmware for the Teensy 4.1 (NXP i.MX RT1062).

Plugs in between a USB device and a host PC. Captures the device's descriptors on the USB2 host port, then presents itself to the PC on USB1 as that same device, forwarding HID interrupt reports in both directions.

Hardware

• Teensy 4.1
• USB host cable on the USB2 port (the one with pads on the bottom of the board)
• USB device cable to the PC on the normal USB1 port

The VBUS power switch is on GPIO_EMC_40 (GPIO8 bit 26).

Display Wiring

An optional TFT display can show live status. Two drivers are supported, selectable at build time with TFT_DRIVER=1 (ST7735, default) or TFT_DRIVER=3 (ILI9341).

Both displays share the same SPI bus (LPSPI4) and control pins:

Signal	Teensy Pin	Notes
SCK	13	SPI clock
MOSI	11	SPI data
CS	10	Chip select (active low)
DC	9	Data/command select
RST	6	Reset (active low)
BL	—	Backlight (GPIO7 bit 17)

Optional: FT6206 Touch (ILI9341 only)

If using an ILI9341 with a capacitive touch panel, enable with TOUCH=1:

Signal	Teensy Pin	Notes
SDA	18	I2C data
SCL	19	I2C clock

Build examples

make TFT=1 -j4                          # ST7735, no touch (default)
make TFT=1 TFT_DRIVER=3 TOUCH=1 -j4    # ILI9341 with touch
make TFT=0 -j4                          # no display

Building

Requires the ARM GCC toolchain. The Makefile expects it at the PlatformIO default path — edit TOOLCHAIN in the Makefile if yours is elsewhere.

make -j4

To enable UART debug output on Serial1 (pin 1 TX, 115200 baud):

make UART=1 -j4

Flash with the Teensy Loader or teensy_loader_cli.

What it does

1. Initializes the USB2 EHCI host controller and waits for a device
2. Resets the port and runs full enumeration — device, config, HID report, and string descriptors
3. Sends SET_CONFIGURATION, SET_IDLE, and SET_PROTOCOL to the device
4. Starts the USB1 device controller, replaying the captured descriptors to the PC
5. Enters a proxy loop: polls interrupt IN endpoints on the host side and forwards reports to the PC via the device side

Supports composite devices with multiple HID interfaces (tested with a Razer Basilisk V3).

Status

Work in progress. Device enumeration and descriptor replay are working. Interrupt report forwarding is under active development.

Files

• core/ — startup code, linker script, boot data
• src/main.c — main proxy flow and LED state machine
• src/usb_host.c — EHCI USB2 host driver (control + interrupt transfers)
• src/usb_device.c — USB1 device controller (descriptor replay + report forwarding)
• src/desc_capture.c — full device enumeration and descriptor capture
• src/uart.c — LPUART6 debug output
• include/imxrt.h — i.MX RT1062 register definitions