Gateware Endpoint Interfaces¶
The LUNA architecture separates gateware into two distinct groups: the core device, responsible for the low-level communications common to all devices, and endpoint interfaces, which perform high-level communications, and which are often responsible for tailoring each device for its intended application:
Every useful LUNA device features at least one endpoint interface capable of at least handling enumeration. Many devices will provide multiple endpoint interfaces – often one for each endpoint – but this is not a requirement. Incoming token, data, and handshake packets are routed to all endpoint interfaces; it is up to each endpoint interface to decide which packets to respond to.
Note: terms like “interface” are overloaded: the single term “interface” can refer both to hardware interfaces and to the USB concept of an Interface. The “interface” in “endpoint interface” is an instance of the former; they are conceptually distinct from USB interfaces. To reduce conflation, we’ll use the full phrase “endpoint interface” in this document.
As a single endpoint interface may handle packets for multiple endpoints; it is entirely possible to have a device that talks on multiple endpoints, but which uses only one endpoint interface.
USBDevice performs no arbitration – if two endpoint interfaces attempt to transmit at the same time, the
result is undefined; and often will result in undesirable output. Accordingly, it’s important to ensure a “clear
delineation of responsibility” across endpoint interfaces. This is often accomplished by ensuring only one endpoint
interface handles a given endpoint or request type.
Provided Endpoint Interfaces¶
The LUNA library ships with a few provided endpoint interfaces. These include:
USBControlEndpoint, which provides gateware that facilitates handling USB control requests. To handle requests via this endpoint, the user attaches one or more request handlers interfaces; which are documented in their own section.
FIFOInterfaceclasses, which implement simple, FIFO-based software interfaces. These lightweight interfaces are meant to allow simple CPU control over one or more endpoints. These are based off of the ValentyUSB
eptriinterface; and will eventually be binary-compatible with existing