USB (Arduino and Adafruit_TinyUSB)

Two USB stacks are present in the core. Users can choose the simpler Pico-SDK version or the more powerful Adafruit TinyUSB library. Use the Tools->USB Stack menu to select between the two.

Pico SDK USB Support

This is the default mode and automatically includes a USB-based serial port, Serial as well as supporting automatic reset-to-upload from the IDE.

The Arduino-Pico core includes ported versions of the basic Arduino Keyboard, Mouse and Joystick libraries. These libraries allow you to emulate a keyboard, a gamepad or mouse (or all together) with the Pico in your sketches.

See the examples and Arduino Reference at and

Adafruit TinyUSB Arduino Support

Examples are provided in the Adafruit_TinyUSB_Arduino for the more advanced USB stack.

To use Serial with TinyUSB, you must include the TinyUSB header in your sketch to avoid a compile error.

#include <Adafruit_TinyUSB.h>

If you need to be compatible with the other USB stack, you can use an ifdef:

#include <Adafruit_TinyUSB.h>

Also, this stack requires sketches to manually call Serial.begin(115200) to enable the USB serial port and automatic sketch upload from the IDE. If a sketch is run without this command in setup(), the user will need to use the standard “hold BOOTSEL and plug in USB” method to enter program upload mode.

Adafruit TinyUSB Configuration and Quirks

The Adafruit TinyUSB’s configuration header for RP2040 devices is stored in libraries/Adafruit_TinyUSB_Arduino/src/arduino/ports/rp2040/tusb_config_rp2040.h (here).

In some cases it is important to know what TinyUSB is configured with. For example, by having set

#define CFG_TUD_CDC 1
#define CFG_TUD_MSC 1
#define CFG_TUD_HID 1
#define CFG_TUD_MIDI 1
#define CFG_TUD_VENDOR 1

this configuration file defines the maximum number of USB CDC (serial) devices as 1. Hence, the example sketch cdc_multi.ino that is delivered with the library will not work, it will only create one USB CDC device instead of two. It will however work when the above CFG_TUD_CDC macro is defined to 2 instead of 1.

To do such a modification when using the Arduino IDE, the file can be locally modified in the Arduino core’s package files. The base path can be found per this article, then navigate further to the packages/rp2040/hardware/rp2040/<core version>/libraries/Adafruit_TinyUSB_Arduino folder to find the Adafruit TinyUSB library.

When using PlatformIO, one can also make use of the feature that TinyUSB allows redirecting the configuration file to another one if a certain macro is set.

    #include "tusb_config.h"

And as such, in the platformio.ini of the project, one can add

build_flags =

and further add create the file include/custom_tusb_config.h as a copy of the original tusb_config_rp2040.h but with the needed modifications.

Note: Some configuration file changes have no effect because upper levels of the library don’t properly support them. In particular, even though the maximum number of HID devices can be set to 2, and two Adafruit_USBD_HID can be created, it will not cause two HID devices to actually show up, because of code limitations.