The XUD library allows the implementation of both full-speed and high-speed USB 2.0 devices on L-Series, G-series and U-Series devices.

For the L and G series the implementation requires the use of an external ULPI transceiver such as the SMSC USB33XX range. U-Series devices include an integrated USB transceiver. Three libraries, with identical API, are provided - one each for L, G and U-Series devices.

Please note, G-series is not recommended for new designs.

The library performs all the low-level I/O operations required to meet the USB 2.0 specification. This processing goes up to and includes the transaction level. It removes all low-level timing requirements from the application, allowing quick development of all manner of USB devices.

The XUD library runs in a single core with endpoint and application cores communicating with it via a combination of channel communication and shared memory variables.

One channel is required per IN or OUT endpoint. Endpoint 0 (the control endpoint) requires two channels, one for each direction. Please note that throughout this document the USB nomenclature is used: an OUT endpoint is used to transfer data from the host to the device, an IN endpoint is used when the host requests data from the device.

An example task diagram is shown in XUD Overview. Circles represent cores running with arrows depicting communication channels between these cores. In this configuration there is one core that deals with endpoint 0, which has both the input and output channel for endpoint 0. IN endpoint 1 is dealt with by a second core, and OUT endpoint 2 and IN endpoint 5 are dealt with by a third core. Cores must be ready to communicate with the XUD library whenever the host demands its attention. If not, the XUD library will NAK.

It is important to note that, for performance reasons, cores communicate with the XUD library using both XC channels and shared memory communication. Therefore, all cores using the XUD library must be on the same tile as the library itself.