# Adafruit TinyUSB Library for Arduino

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This library is a Arduino-friendly version of [TinyUSB](https://github.com/hathach/tinyusb) stack.
It is designed with structure and APIs that are easily integrated to an Arduino Core.

## Features

### Device Stack

Supported device class drivers are:

- Communication (CDC): which is used to implement `Serial` monitor
- Human Interface Device (HID): Generic (In & Out), Keyboard, Mouse, Gamepad etc ...
- Mass Storage Class (MSC): with multiple LUNs
- Musical Instrument Digital Interface (MIDI)
- WebUSB with vendor specific class

### Host Stack

Host support is still work-in-progress but currently available with rp2040 core thanks to [Pico-PIO-USB](https://github.com/sekigon-gonnoc/Pico-PIO-USB). Supported class driver are:

- Communication (CDC)
- MassStorage class

## Supported Cores

There are 2 type of supported cores: with and without built-in support for TinyUSB. Built-in support provide seamless integration but requires extra code added to core's source code. Unfortunately it is not always easy or possible to make those modification.

### Cores with built-in support

Following core has TinyUSB as either the primary usb stack or selectable via menu `Tools->USB Stack`. You only need to include `<Adafruit_TinyUSB.h>` in your sketch to use.

- [adafruit/Adafruit_nRF52_Arduino](https://github.com/adafruit/Adafruit_nRF52_Arduino)
- [adafruit/ArduinoCore-samd](https://github.com/adafruit/ArduinoCore-samd)
- [earlephilhower/arduino-pico](https://github.com/earlephilhower/arduino-pico)
- [espressif/arduino-esp32](https://github.com/espressif/arduino-esp32)

  ESP32 port relies on Espressif's [esp32-hal-tinyusb.c](https://github.com/espressif/arduino-esp32/blob/master/cores/esp32/esp32-hal-tinyusb.c) for building usb descriptors which requires all descriptors must be specified in usb objects declaration i.e constructors. Therefore all descriptor-related fields must be part of object declaration and descriptor-related API have no effect afterwards for this port. 

### Cores without built-in support

Following is cores without built-in support

- **mbed_rp2040**

It is still possible to use TinyUSB but with some limits such as:

- `TinyUSB_Device_Init()` need to be manually called in setup()
- `TinyUSB_Device_Task()` and/or `TinyUSB_Device_FlushCDC()` may (or not) need to be manually called in loop()
- Use `SerialTinyUSB` name instead of Serial for serial monitor
- And there could be more other issues, using on these cores should be considered as experimental

## Class Driver API

More document to write ... 

## Porting Guide

To integrate TinyUSB library to a Arduino core, you will need to make changes to the core for built-in support and library for porting the mcu/platform.

### Arduino Core Changes

If possible, making changes to core will allow it to have built-in which make it almost transparent to user sketch 

1. Add this repo as submodule (or have local copy) at your ArduioCore/libraries/Adafruit_TinyUSB_Arduino (much like SPI).
2. Since Serial as CDC is considered as part of the core, we need to have `#include "Adafruit_USBD_CDC.h"` within your `Arduino.h`. For this to work, your `platform.txt` include path need to have `"-I{runtime.platform.path}/libraries/Adafruit_TinyUSB_Arduino/src/arduino"`.
3. In your `main.cpp` before setup() invoke the `TinyUSB_Device_Init(rhport)`. This will initialize usb device hardware and tinyusb stack and also include Serial as an instance of CDC class.
4. `TinyUSB_Device_Task()` must be called whenever there is new USB event. Depending on your core and MCU with or without RTOS. There are many ways to run the task. For example:
  - Use USB IRQn to set flag then invoke function later on after exiting IRQ.
  - Just invoke function after the loop(), within yield(), and delay()
5. `TinyUSB_Device_FlushCDC()` should also be called often to send out Serial data as well.
6. Note: For low power platform that make use of WFI()/WFE(), extra care is required before mcu go into low power mode. Check out my PR to circuipython for reference https://github.com/adafruit/circuitpython/pull/2956

### Library Changes

In addition to core changes, library need to be ported to your platform. Don't worry, tinyusb stack has already done most of heavy-lifting. You only need to write a few APIs

1. `TinyUSB_Port_InitDevice()` hardware specific (clock, phy) to enable usb hardware then call tud_init(). This API is called as part of TinyUSB_Device_Init() invocation.
2. `TinyUSB_Port_EnterDFU()` which is called when device need to enter DFU mode, usually by touch1200 feature
3. `TinyUSB_Port_GetSerialNumber()` which is called to get unique MCU Serial ID to used as Serial string descriptor.