NXP Semiconductors LPC43 Series User Manual

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NXP Semiconductors LPC43 Series User Manual Manual pdf 576 page image

UM10503 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2012. All rights reserved.User manual Rev. 1.3 — 6 July 2012 576 of 1269NXP Semiconductors UM10503Chapter 23: LPC43xx USB0 Host/Device/OTG controller• Write the Active bit in the status field to “0”.• Write the Halt bit in the status field to “0”.Remark: The DCD must only modify dQH if the associated endpoint is not primed andthere are no outstanding dTD’s.23.10.10.2 Operational model for setup transfersAs discussed in section Control Endpoint Operational Model (Section 23.10.8), a setuptransfer requires special treatment by the DCD. A setup transfer does not use a dTD butinstead stores the incoming data from a setup packet in an 8-byte buffer within the dQH.Upon receiving notification of the setup packet, the DCD should handle the setup transferas demonstrated here:1. Copy the setup buffer contents from dQH - RX to software buffer.2. Acknowledge setup backup by writing a “1” to the corresponding bit inENDPTSETUPSTAT.Remark: The acknowledge must occur before continuing to process the setup packet.Remark: After the acknowledge has occurred, the DCD must not attempt to accessthe setup buffer in the dQH – RX. Only the local software copy should be examined.3. Check for pending data or status dTD’s from previous control transfers and flush if anyexist as discussed in section Flushing/De-priming an Endpoint.Remark: It is possible for the device controller to receive setup packets beforeprevious control transfers complete. Existing control packets in progress must beflushed and the new control packet completed.4. Decode setup packet and prepare data phase [optional] and status phase transfer asrequire by the USB Specification Chapter 9 or application specific protocol.23.10.11 Managing transfers with transfer descriptors23.10.11.1 Software link pointersIt is necessary for the DCD software to maintain head and tail pointers to the linked list ofdTDs for each respective queue head. This is necessary because the dQH only maintainspointers to the current working dTD and the next dTD to be executed. The operationsdescribed in following sections for managing dTD will assume the DCD can reference thehead and tail of the dTD linked list.Remark: To conserve memory, the reserved fields at the end of the dQH can be used tostore the Head & Tail pointers but it still remains the responsibility of the DCD to maintainthe pointers.