Intervene in USB Controller I/O Streams with an MCU Interposer

Series: alt.ctrl activities; builds on Game controllers

Many modern MCUs have a USB device connector and can also support an additional USB host port, sometimes referred to as an OTG (on-the-go) port.

Materials

MCUs with USB host ports, and the cables sometimes required to plug common game controllers into them
Item	Amazon	Adafruit	SparkFun	Waveshare	Mouser	Digi-Key
Photo: Liz Clark, Adafruit (source), CC BY-SA 3.0 Adafruit Feather RP2040 with USB Type A Host		5723			485-5723
ESP32-S3 boards with two USB-C ports (here an N16R8: 16 MB flash, 8 MB PSRAM), in the style of Espressif's ESP32-S3-DevKitC-1: one port is the ESP32-S3's native USB OTG, the other a USB-to-UART bridge	B0GBT212KM
Waveshare RP2350A USB Mini (RP2350-USB-A): USB-C for programming, and a USB-A host port driven by the RP2350's PIO	B0DW8Z2K7C			30274
Teensy 4.1: a USB host port on a 5-pin header			DEV-16771			1568-16771-ND
USB Host Cable for Teensy 4.1: the 5-pin host header to a USB-A socket			CAB-28389			1568-CAB-28389-ND
Teensy 4.0: USB host on two pads on the underside, data only; the board does not power the USB device			DEV-15583		474-DEV-15583
USB-A socket to micro-USB plug OTG adapters, 2 pack: for host ports with a micro-USB socket, such as the USB Host BFF's	B0BX9FSCFH	2910
Other cables for common game controllers: to be supplied.

Affordable USB host adapters based on the Maxim MAX3421E
Item	Amazon	Adafruit	SparkFun	M5Stack	Mouser
Photo: Liz Clark, Adafruit (source), CC BY-SA 3.0 Adafruit USB Host FeatherWing with MAX3421E		5858			485-5858
Photo: Liz Clark, Adafruit (source), a still from the original animation, CC BY-SA 3.0 Adafruit USB Host BFF for QT Py or Xiao with MAX3421E, with a micro-B OTG port		5956			485-5956
M5Stack Module USB v1.2 (MAX3421E), for the Basic, Core2 and CoreS3 controllers				M020-V12	170-M020-V12
Photo: SparkFun Electronics, CC BY-NC-SA 3.0 (SparkFun, 2011) SparkFun USB-C Host Shield with MAX3421E, an Arduino shield: the MAX3421E on the hardware SPI pins (D10–D13), and a USB-C socket that supplies 5 V to the device			DEV-21247		474-DEV-21247
Mini USB Host Shield 2.0, SPI, sized for the Arduino Pro Mini. Amazon's listing does not name its chip; other sellers' listings of this board give the MAX3421E, 3.3 V and a USB-A socket	B0DC9MFKJR

Tools

Tools not yet listed.

Skills

Programming an MCU with a USB host library

Instructions

With the controller attached, identify the closest existing device that the host library already supports.
Test that, then expand it with the special features the particular device exposes.
Identify a USB profile similar to the device's, and create a pass-through that attempts to provide everything the controller does.
Once this is tested, you can write your own remappings.

Variations

Variations not yet written.

Related resources

Libraries: USB Host Shield Library 2.0, the Arduino library for MAX3421E host adapters, with drivers for HID devices and for Xbox, PS3, PS4, PS5, Switch Pro and Wii controllers
Adafruit TinyUSB for Arduino: USB host through a MAX3421E, or on the RP2040 through Pico-PIO-USB
Pico-PIO-USB: USB host through the PIO of the RP2040 and RP2350
USBHost_t36, PJRC's USB host library for the Teensy, with a joystick driver
Adafruit: DIY Turbo Button Controller - HID Remapper, a Feather RP2040 USB Host that passes a gamepad through and adds a turbo button
Adafruit guides: Feather RP2040 with USB Type A Host, USB Host FeatherWing with MAX3421E, USB Host BFF and Using a Keyboard with USB Host
PJRC forum: T3.6 USB Host - Joysticks, on extending USBHost_t36's game controller support (PS3, PS4, Xbox)

Coding Prompt Build Block

A prompt to give a coding assistant, to start the code for this activity. Copy the box, answer its questions about your board and pins, and test what comes back on the bench before you rely on it.

I am building "Intervene in USB Controller I/O Streams with an MCU Interposer", the activity at https://adrianfreed.com/usb-controller-mcu-interposer.html.

Write a program for a microcontroller with a USB host port that sits between a USB game controller and a computer. First, list the controller's descriptors and print its reports as they arrive, so that we can see what each control sends.

Then find the closest device that the host library already supports, and test that. Then make a pass-through: the microcontroller appears to the computer as a USB device of a similar kind, and passes on everything the controller does. Then add remappings, each in its own small function: swapping buttons, scaling an axis, adding a turbo button.

If the board cannot be a USB host and a USB device at once (on an ESP32-S3, the USB host takes the peripheral that the USB device stack would use), send the data to the computer another way, such as serial over the board's other port.

Libraries to explore:

Adafruit TinyUSB for Arduino: USB device and host: host through a MAX3421E, or on the RP2040 through Pico-PIO-USB; its DualRole examples are both at once: hid_device_report prints a device's reports, and hid_remapper passes a keyboard's reports on to the computer, changed (https://github.com/adafruit/Adafruit_TinyUSB_Arduino)
Pico-PIO-USB: USB host or device through the PIO of the RP2040 and RP2350 (https://github.com/sekigon-gonnoc/Pico-PIO-USB)
USBHost_t36: PJRC's USB host library for the Teensy, with a joystick driver (https://github.com/PaulStoffregen/USBHost_t36)
USB Host Shield Library 2.0: the Arduino library for MAX3421E host adapters, with drivers for HID devices and for Xbox, PS3, PS4, PS5, Switch Pro and Wii controllers (https://github.com/felis/USB_Host_Shield_2.0)
M5-Max3421E-USBShield: M5Stack's library and examples for its USB modules (MAX3421E), built on Adafruit TinyUSB (https://github.com/m5stack/M5-Max3421E-USBShield)
Arduino-ESP32 USB Host API: USB host for HID devices, including gamepads, and for serial adapters and storage, on the ESP32-S2, ESP32-S3 and ESP32-P4; the host needs the USB peripheral that the board's USB device stack would otherwise hold (https://docs.espressif.com/projects/arduino-esp32/en/latest/api/usb_host.html)

Before writing anything, ask me what I am using: the board and its pins, or the software (such as Max, Pd or Python), and check its documentation for what this needs. Put the pin numbers, ranges and other settings in one block at the top, each with a comment. Say which of the libraries above you use, and why. Start with a test that shows the raw readings, so that I can check the wiring and the ranges before the rest.

This activity by Adrian Freed is licensed under Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0): you may share and adapt it with attribution, for non-commercial purposes such as personal projects and teaching, and you must share adaptations under the same licence. Product names and links belong to their suppliers.