Texas Instruments TMS320DM643X DMP manual Transmit and Receive Descriptor Queues

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Peripheral Architecture

2.5.2Transmit and Receive Descriptor Queues

The EMAC module processes descriptors in linked list chains as discussed in Section 2.5.1. The lists controlled by the EMAC are maintained by the application software through the use of the head descriptor pointer registers (HDP). Since the EMAC supports eight channels for both transmit and receive, there are eight head descriptor pointer registers for both. They are:

∙TXnHDP - Transmit Channel n DMA Head Descriptor Pointer Register

∙RXnHDP - Receive Channel n DMA Head Descriptor Pointer Register

After an EMAC reset and before enabling the EMAC for send or receive, all 16 head descriptor pointer registers must be initialized to 0.

The EMAC uses a simple system to determine if a descriptor is currently owned by the EMAC or by the application software. There is a flag in the buffer descriptor flags called OWNER. When this flag is set, the packet that is referenced by the descriptor is considered to be owned by the EMAC. Note that ownership is done on a packet based granularity, not on descriptor granularity, so only SOP descriptors make use of the OWNER flag. As packets are processed, the EMAC patches the SOP descriptor of the corresponding packet and clears the OWNER flag. This is an indication that the EMAC has finished processing all descriptors up to and including the first with the EOP flag set, indicating the end of the packet (note this may only be one descriptor with both the SOP and EOP flags set).

To add a descriptor or a linked list of descriptors to an EMAC descriptor queue for the first time, the software application simply writes the pointer to the descriptor or first descriptor of a list to the corresponding HDP register. Note that the last descriptor in the list must have its “next”pointer cleared to

0.This is the only way the EMAC has of detecting the end of the list. So in the case where only a single descriptor is added, its “nextdescriptor” pointer must be initialized to 0.

The HDP must never be written to a second time while a previous list is active. To add additional descriptors to a descriptor list already owned by the EMAC, the NULL “next”pointer of the last descriptor of the previous list is patched with a pointer to the first descriptor in the new list. The list of new descriptors to be appended to the existing list must itself be NULL terminated before the pointer patch is performed.

There is a potential race condition where the EMAC may read the “next”pointer of a descriptor as NULL in the instant before an application appends additional descriptors to the list by patching the pointer. This case is handled by the software application always examining the buffer descriptor flags of all EOP packets, looking for a special flag called end of queue (EOQ). The EOQ flag is set by the EMAC on the last descriptor of a packet when the descriptor’s “next”pointer is NULL. This is the way the EMAC indicates to the software application that it believes it has reached the end of the list. When the software application sees the EOQ flag set, and there are more descriptors to process, the application may at that time submit the new list, or the portion of the appended list that was missed, by writing the new list pointer to the same HDP that started the process.

This process applies when adding packets to a transmit list, and empty buffers to a receive list.

18 Ethernet Media Access Controller (EMAC)/SPRU941A –April 2007

Management Data Input/Output (MDIO)

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Contents Users Guide Submit Documentation Feedback Contents MAC Hash Address Register 1 MACHASH1 Appendix a Appendix BList of Figures Transmit Pacing Algorithm Test Register Tpacetest List of Tables Fifo Control Register Fifocontrol Field Descriptions Read This First Features Purpose of the PeripheralFunctional Block Diagram Emac and Mdio Block DiagramClock Control Signal DescriptionsIndustry Standards Compliance Statement Memory MapEmac and Mdio Signals Signal Type DescriptionEthernet Frame Description Ethernet Protocol OverviewEthernet Frame Format Field Bytes DescriptionEthernet’s Multiple Access Protocol Programming InterfacePacket Buffer Descriptors Basic Descriptor Description Typical Descriptor Linked ListTransmit and Receive Descriptor Queues Transmit and Receive Emac Interrupts Transmit Buffer Descriptor Format Example 1. Transmit Buffer Descriptor in C Structure FormatBuffer Offset Next Descriptor PointerBuffer Pointer Buffer LengthEnd of Queue EOQ Flag End of Packet EOP FlagOwnership Owner Flag Teardown Complete Tdowncmplt FlagReceive Buffer Descriptor Format Receive Buffer Descriptor FormatExample 2. Receive Buffer Descriptor in C Structure Format #define EmacdscflagjabberBuffer Length CRC Error Crcerror Flag Code Error Codeerror FlagAlignment Error Alignerror Flag Jabber FlagInternal Memory Emac Control ModuleNo Match Nomatch Flag Bus ArbiterMdio Module Interrupt ControlMdio Module Components Global PHY Detection and Link State Monitoring PHY Register User AccessMdio Clock Generator Active PHY MonitoringMdio Module Operational Overview Initializing the Mdio Module Writing Data To a PHY RegisterReading Data From a PHY Register Example of Mdio Register Access Code Example 3. Mdio Register Access MacrosReceive DMA Engine Emac ModuleEmac Module Components Receive FifoTransmit Fifo Clock and Reset LogicTransmit DMA Engine MAC TransmitterReceive Control Media Independent Interface MIIData Reception Receive Inter-Frame IntervalCollision-Based Receive Buffer Flow Control Ieee 802.3x-Based Receive Buffer Flow ControlAdaptive Performance Optimization APO Transmit ControlCRC Insertion Interpacket-Gap IPG EnforcementTransmit Flow Control Speed, Duplex, and Pause Frame SupportReceive Channel Enabling Receive DMA Host ConfigurationPacket Receive Operation Receive Address MatchingHardware Receive QOS Support Host Free Buffer TrackingReceive Channel Teardown Promiscuous Receive Mode Receive Frame ClassificationReceive Frame Treatment Summary Receive Frame TreatmentReceive Overrun Middle of Frame Overrun TreatmentMiddle of Frame Overrun Treatment Receive and Transmit Latency Transmit DMA Host ConfigurationPacket Transmit Operation Transmit Channel TeardownReset Considerations Software Reset ConsiderationsTransfer Node Priority Enabling the EMAC/MDIO Peripheral Hardware Reset ConsiderationsInitialization Emac Control Module InitializationExample 4. Emac Control Module Initialization Code Mdio Module InitializationExample 5. Mdio Module Initialization Code Emac Module Initialization Transmit Packet Completion Interrupts Interrupt SupportEmac Module Interrupt Events and Requests Receive Packet Completion InterruptsHost Error Interrupt Statistics InterruptLink Change Interrupt User Access Completion InterruptMdio Module Interrupt Events and Requests Proper Interrupt ProcessingPower Management Emulation ConsiderationsEmulation Control Acronym Register Description Emac Control Module Interrupt Control Register EwctlEmac Control Module Registers Bit FieldEmac Control Module Interrupt Timer Count Register Ewinttcnt Mdio Version Register Version Management Data Input/Output Mdio RegistersMdio Version Register Version Field Descriptions Mdio Control Register Control Mdio Control Register Control Field DescriptionsPHY Acknowledge Status Register Alive Field Descriptions PHY Acknowledge Status Register AlivePHY Link Status Register Link PHY Link Status Register Link Field DescriptionsNo Mdio link change event Will clear the event and writing a 0 has no effect No Mdio user command complete event USERINTMASKED0 and USERINTMASKED1 correspond to USERACCESS0 WS-0 Userintmaskclear Mdio User Access Register 0 USERACCESS0 Mdio User Access Register 0 USERACCESS0 Field DescriptionsPhyadrmon Mdio User PHY Select Register 0 USERPHYSEL0Linksel Linkintenb Bit Field Value DescriptionMdio User Access Register 1 USERACCESS1 Mdio User Access Register 1 USERACCESS1 Field DescriptionsMdio User PHY Select Register 1 USERPHYSEL1 Mdio User PHY Select Register 1 USERPHYSEL1Ethernet Media Access Controller Emac Registers Ethernet Media Access Controller Emac Registers Offset Acronym Register DescriptionOffset Acronym Register Description Network Statistics RegistersTransmit Identification and Version Register Txidver Transmit Control Register TxcontrolTransmit Control Register Txcontrol Field Descriptions Transmit Teardown Register Txteardown Transmit Teardown Register Txteardown Field DescriptionsTxtdnch Receive Identification and Version Register Rxidver Receive Control Register RxcontrolReceive Control Register Rxcontrol Field Descriptions Receive Teardown Register Rxteardown Receive Teardown Register Rxteardown Field DescriptionsRxtdnch Transmit Interrupt Status Unmasked Register Txintstatraw TX7PENDTransmit Interrupt Status Masked Register Txintstatmasked Transmit Interrupt Status Masked Register TxintstatmaskedTransmit Interrupt Mask Set Register Txintmaskset TX7MASKTransmit Interrupt Mask Clear Register Txintmaskclear Transmit Interrupt Mask Clear Register TxintmaskclearUserint Linkint MAC Input Vector Register MacinvectorMAC Input Vector Register Macinvector Field Descriptions Hostpend Statpend Rxpend TxpendReceive Interrupt Status Unmasked Register Rxintstatraw RX7PENDReceive Interrupt Status Masked Register Rxintstatmasked Receive Interrupt Status Masked Register RxintstatmaskedReceive Interrupt Mask Set Register Rxintmaskset RX7MASKReceive Interrupt Mask Clear Register Rxintmaskclear Receive Interrupt Mask Clear Register RxintmaskclearMAC Interrupt Status Unmasked Register Macintstatraw MAC Interrupt Status Masked Register MacintstatmaskedHostpend Statpend Hostmask Statmask MAC Interrupt Mask Set Register MacintmasksetMAC Interrupt Mask Clear Register Macintmaskclear HostmaskRxcsfen Rxcefen Rxcafen Rxpasscrc Rxqosen RxnochainRxcmfen RxpromchFrames containing errors are filtered Receive multicast channel select Receive Unicast Enable Set Register Rxunicastset RXCH7ENReceive Unicast Clear Register Rxunicastclear Receive Unicast Clear Register RxunicastclearReceive Maximum Length Register Rxmaxlen Receive Buffer Offset Register RxbufferoffsetReceive Maximum Length Register Rxmaxlen Field Descriptions Rxfilterthresh Reserved RX nFLOWTHRESH FFhReceive Channel 0-7 Free Buffer Count Register RXnFREEBUFFER MAC Control Register Maccontrol MAC Control Register Maccontrol Field DescriptionsSent. Full-duplex mode no outgoing pause frames are sent LoopbackMAC Status Register Macstatus MAC Status Register Macstatus Field DescriptionsMAC Status Register Macstatus Field Descriptions Bit Field Value DescriptionEmulation Control Register Emcontrol Field Descriptions Emulation Control Register EmcontrolFifo Control Register Fifocontrol Fifo Control Register Fifocontrol Field DescriptionsMAC Configuration Register Macconfig Field Descriptions MAC Configuration Register MacconfigSoft Reset Register Softreset Soft Reset Register Softreset Field DescriptionsMAC Source Address Low Bytes Register Macsrcaddrlo MAC Source Address High Bytes Register MacsrcaddrhiMAC Hash Address Register 1 MACHASH1 Field Descriptions MAC Hash Address Register 1 MACHASH1MAC Hash Address Register 2 MACHASH2 MAC Hash Address Register 2 MACHASH2 Field DescriptionsBack Off Test Register Bofftest Transmit Pacing Algorithm Test Register TpacetestBack Off Test Register Bofftest Field Descriptions Receive Pause Timer Register Rxpause Field Descriptions Receive Pause Timer Register RxpauseTransmit Pause Timer Register Txpause Transmit Pause Timer Register Txpause Field DescriptionsMAC Address Low Bytes Register Macaddrlo MAC Address High Bytes Register MacaddrhiMAC Address Low Bytes Register Macaddrlo Field Descriptions MAC Index Register Macindex MAC Index Register Macindex Field DescriptionsMacindex TX nHDP Transmit Channel 0-7 Completion Pointer Register TXnCP Receive Channel 0-7 Completion Pointer Register RXnCPBroadcast Receive Frames Register Rxbcastframes Network Statistics RegistersGood Receive Frames Register Rxgoodframes Multicast Receive Frames Register RxmcastframesPause Receive Frames Register Rxpauseframes Receive CRC Errors Register RxcrcerrorsReceive Alignment/Code Errors Register Rxaligncodeerrors Receive Oversized Frames Register RxoversizedReceive Frame Fragments Register Rxfragments Receive Jabber Frames Register RxjabberReceive Undersized Frames Register Rxundersized Filtered Receive Frames Register RxfilteredReceive QOS Filtered Frames Register Rxqosfiltered Receive Octet Frames Register RxoctetsGood Transmit Frames Register Txgoodframes Pause Transmit Frames Register Txpauseframes Broadcast Transmit Frames Register TxbcastframesMulticast Transmit Frames Register Txmcastframes Deferred Transmit Frames Register TxdeferredTransmit Multiple Collision Frames Register Txmulticoll Transmit Underrun Error Register TxunderrunTransmit Single Collision Frames Register Txsinglecoll Transmit Late Collision Frames Register TxlatecollTransmit Carrier Sense Errors Register Txcarriersense Transmit Octet Frames Register TxoctetsTransmit and Receive 64 Octet Frames Register FRAME64 Network Octet Frames Register Netoctets Receive DMA Overruns Register Rxdmaoverruns Appendix a Glossary Table A-1. Physical Layer Definitions Term DefinitionTable B-1. Document Revision History Reference Additions/Modifications/DeletionsProducts Applications DSP
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