Universal Serial Bus InterfaceMCF5253 Reference Manual, Rev. 1Freescale Semiconductor 24-13324.11.3.1.1 StallingThere are two occasions where the USB_DR may need to return to the host a STALL.The first occasion is the functional stall, which is a condition set by the DCD as described in the USB 2.0Specification, Chapter 9, Device Framework. A functional stall is only used on non-control endpoints andcan be enabled in the device controller by setting the endpoint stall bit in the ENDPTCTRLn registerassociated with the given endpoint and the given direction. In a functional stall condition, the devicecontroller will continue to return STALL responses to all transactions occurring on the respective endpointand direction until the endpoint stall bit is cleared by the DCD.A protocol stall, unlike a function stall, is used on control endpoints is automatically cleared by the devicecontroller at the start of a new control transaction (setup phase). When enabling a protocol stall, the DCDshould enable the stall bits (both directions) as a pair. A single write to the ENDPTCTRLn register canensure that both stall bits are set at the same instant.NOTEAny write to the ENDPTCTRLn register during operational mode mustpreserve the endpoint type field (that is, perform a read-modify-write).24.11.3.2 Data ToggleData toggle is a mechanism to maintain data coherency between host and device for any given data pipe.For more information on data toggle, refer to the USB 2.0 specification.24.11.3.2.1 Data Toggle ResetThe DCD may reset the data toggle state bit and cause the data toggle sequence to reset in the devicecontroller by writing a '1' to the data toggle reset bit in the ENDPTCTRLn register. This should only benecessary when configuring/initializing an endpoint or returning from a STALL condition.Endpoint Type 00 Control01 Isochronous10 Bulk11 InterruptEndpoint Stall 0Table 24-82. Device Controller Stall Response MatrixUSB Packet EndpointStall BitEffect onSTALL Bit USB ResponseSETUP packet received by a non-control endpoint. N/A None STALLIN/OUT/PING packet received by a non-control endpoint. 1 None STALLIN/OUT/PING packet received by a non-control endpoint. 0 None ACK/NAK/NYETSETUP packet received by a control endpoint. N/A Cleared ACKIN/OUT/PING packet received by a control endpoint 1 None STALLIN/OUT/PING packet received by a control endpoint. 0 None ACK/NAK/NYETTable 24-81. Device Controller Endpoint Initialization (continued)Field Value
