Instead of directly stalling an endpoint, handlers should enable the
halt condition on an usbus endpoint to signal error condition.
This can then be cleared via a CLEAR FEATURE request from the host.
This commit adds support for URBs (USB Request/Response Blocks). These
allow for submitting multi-transfer sized buffers with USBUS handling
the individual usbdev xmits. Multiple URBs can be queued at once for a
single endpoint and USBUS will handle them in the order of submission.
OUT endpoint URBs must always consist of a whole number of full-sized
transfers (N x MaxEndpointSize). They will automatically finish after
the endpoint received a transfer less than the endpoint size.
IN endpoints can be arbitrary-sized and do not have to consist of a
whole number of full-sized transmissions. They support a flag to
indicate that the last transfer in the sequence must be less than a full
sized transfer (USBUS_URB_FLAG_AUTO_ZLP) and this adds a zero length
transfer at the end of the transmissions if the last transfer was equal
to the maximum transfer size.
URBs can be cancelled, but if the URB is already being processed it will
be cancelled after the current transmission within the URB is finished.
If it is still in the queue it will immediately be removed from the
queue.
This commit changes the name of the requests over the control endpoints
to control requests instead of setup requests. This is a terminology fix
to follow the USB specification more closely as technically only the
first stage of a control request is named setup which contains a setup
packet. The whole transfer is a control transfer.
