Intel IXP400 IxUSB Send and Receive Requests, IxUSB Endpoint Stall Feature, Frame Synchronization

Intel® IXP400 Software

Access-Layer Components: USB Access (ixUSB) API

22.4.1.2Frame Synchronization

The SYNCH_FRAME request is used by isochronous endpoints that use implicit-pattern synchronization. The isochronous endpoints may need to track frame numbers in order to maintain synchronization.

Isochronous-endpoint transactions may vary in size, according to a specific repeating pattern. The host and endpoint must agree on which frame begins the repeating pattern. The host uses this request to specify the exact frame on which the repeating pattern begins.

The data stage of the SYNCH_FRAME request contains the frame number in which the pattern begins. Having received the frame number, the device can start monitoring each frame number sent during the SOF. This is recorded in the frame counter and made available through specific driver functions (see ixUSBFrameCounterGet).

22.4.2ixUSB Send and Receive Requests

The USB access layer encodes and decodes data frames sending and receiving buffers to and from the client in the same format as IX_MBUF.

Buffers are sent from the UDC to the host with the ixUSBBufferSubmit API.

Data buffers are received from the host through the callback function registered with the access layer during the ixUSBReceiveCallbackRegister API call.

22.4.3ixUSB Endpoint Stall Feature

A device uses the STALL handshake in one of two distinct occasions.

The first case — known as “functional stall” — is when the Halt feature, associated the endpoint, is set. A special case of the functional stall is the “commanded stall.” Commanded stall occurs when the host explicitly sets the endpoint’s Halt feature using the SET_FEATURE command.

Once a function’s endpoint is halted, the function must continue returning STALL packets until the condition causing the halt has been cleared through host intervention (using SET_FEATURE). This can happen both for IN and OUT endpoints. In the case of IN endpoints, the endpoint sends a STALL handshake immediately after receiving an IN token. For OUT endpoints the STALL handshake is sent as soon as the data packet after the OUT token is received.

Figure 102. STALL on IN Transactions

Host
	Device
IN Token
	STALL
	Bus
Request	Reply
	B2418-01

Programmer’s Guide	IXP400 Software Version 2.0	April 2005
	Document Number: 252539, Revision: 007	305