USB Composite library for STM32F1

Protocols supported

standard USB HID, with many built-in profiles, and customizable with more
MIDI over USB
XBox360 controller (only controller-to-host is currently supported)
Mass storage

Basic concepts

Start with:

#include <USBComposite.h>

The library defines one central singleton object:

extern USBCompositeDevice USBComposite;

This controls USB device identification as well as registers the plugins that are connected to it.

Plugin classes included in the library:

USBHID
USBMIDI
USBXBox360
USBMassStorage
USBCompositeSerial

To use them, you need to create instances of them. Currently, only one instance of each plugin class can be created.

If you want to make a simple (non-composite) USB device, you can create an instance of the plugin class and call the begin() method, and it will take care of registering itself with USBComposite and starting up USBComposite. If you want to make a composite USB device, however, you need to control the device with USBComposite:

USBComposite.clear(); // clear any plugins previously registered
plugin1.registerComponent(); 
plugin2.registerComponent();
USBComposite.begin();

Of course, you may need to do some further configuring of the plugins or the USBComposite device before the USBComposite.begin() call.

Finally, there are a number of classes that implement particular protocols for the USBHID class plugin. These are:

HIDMouse
HIDKeyboard
HIDJoystick
HIDAbsMouse
HIDConsumer
HIDRaw<txSize,rxSize>

And you can customize with more. Moreover, the USBHID plugin itself allows for compositing multiple HID profiles, e.g., Mouse / Keyboard / three joysticks. Each of these has at least one required parameter, which is an instance of USBHID.

Not all combinations will fit within the constraints of the STM32F1 USB system, and not all combinations will be supported by all operating systems.

I recommend calling USBComposite.setDeviceId(device) with a different device number for each combination of plugins and profiles to prevent problems with cached configurations on the host computer.

Simple USB device configuration

A simple USB device uses a single plugin. You need to create an instance of the plugin class, call any setup methods for the plugin and the begin() method for the plugin. For instance, to inject keyboard data, you should do:

USBHID HID; // create instance of USBHID plugin
HIDKeyboard Keyboard(HID); // create a profile

HID.begin(HID_KEYBOARD);

and then call Keyboard.print("TextToInject") to inject keyboard data. Some plugin configurations may require further initialization code or further code that needs to be called inside the Arduino loop() function.

See the BootKeyboard, midiout and x360 example code for this procedure.

(Additionally, the USBHID plugin has a convenience begin() method that lets you include an instance of a USBCompositeSerial plugin class, and that creates a composite HID-Serial device.)

However, if you want a USB device using more than one plugin, then you will NOT call the plugin's begin() method.

Memory limitations

There are 320 bytes of hardware buffer memory available after endpoint 0 is taken into account. The following are the default buffer memory needs of the current components:

USB Serial: 144 bytes
USB HID: 64 bytes
USB Mass Storage: 128 bytes
USB MIDI: 128 bytes
XBox360 Controller: 64 bytes

This places a limit on what combinations can be used together. For instance, HID+Mass storage+MIDI should be theoretically OK (320 bytes), but Serial+HID+Mass storage (336 bytes) will fail with default settings (and return false from USBComposite.begin()) due to lack of memory.

However, USB Serial, USB HID and USB MIDI allow you to decrease buffer sizes (and allow for more complex composite devices) by calling:

USBHID HID;
USBCompositeSerial CompositeSerial;
USBMIDI MIDI;

CompositeSerial.setRXPacketSize(size);
CompositeSerial.setTXPacketSize(size);
HID.setTXPacketSize(size); 
MIDI.setRXPacketSize(size);
MIDI.setTXPacketSize(size);

The maximum and default packet size is 64. Smaller packet sizes have not been thoroughly tested and may slow things down. In particular, for HID you should make sure your packet size is sufficient for your largest HID report. The CompositeSerial device also has a control channel whose 16 byte packet size is not adjustable.

Note that in the above, RX and TX are from the point of view of the MCU, not the host (i.e., RX corresponds to USB Out and TX to USB In).

Endpoint limitations

There is one bidirectional endpoint 0 that all endpoints share, and the hardware allows for seven more. Here are how many endpoints besides endpoint 0 are needed for each plugin:

USB Serial: 3
USB HID: 1
USB Mass Storage: 2
USB MIDI: 2
XBox360 Controller: 2