Texas Instruments TMS320DM36X manual Transmit and Receive Descriptor Queues

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Architecture

2.6.2Transmit and Receive Descriptor Queues

The EMAC module processes descriptors in linked list chains as discussed in Section 2.6.1. 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 “next descriptor” 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.

SPRUFI5B –March 2009 –Revised December 2010 Ethernet Media Access Controller (EMAC)/Management Data Input/Output 21

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© 2009–2010, Texas Instruments Incorporated

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Contents Users Guide Submit Documentation Feedback Mdio Registers Mdio Version Register Version Mdio Control Register Control Appendix B Appendix aList of Figures Transmit Interrupt Mask Set Register Txintmaskset List of Tables MAC Control Register Maccontrol Field Descriptions Read This First Related Documentation From Texas Instruments Related Documentation From Texas Instruments Purpose of the Peripheral FeaturesEmac and Mdio Block Diagram Functional Block DiagramIndustry Standards Compliance Statement Clock ControlMII Clocking Signal Descriptions Memory MapMedia Independent Interface MII Connections Emac and Mdio Signals for MII Interface Signal Type DescriptionPin Multiplexing Ethernet Frame Format Ethernet Protocol OverviewEthernet Frame Description Field Bytes DescriptionProgramming Interface Ethernet’s Multiple Access ProtocolPacket Buffer Descriptors WordField Field Description Basic Descriptor DescriptionTransmit and Receive Descriptor Queues Transmit and Receive Emac Interrupts Example 1. Transmit Buffer Descriptor in C Structure Format Transmit Buffer Descriptor FormatBuffer Pointer Next Descriptor PointerBuffer Offset Buffer LengthOwnership Owner Flag End of Packet EOP FlagEnd of Queue EOQ Flag Teardown Complete Tdowncmplt FlagReceive Buffer Descriptor Format Receive Buffer Descriptor FormatExample 2. Receive Buffer Descriptor in C Structure Format Buffer Length Alignment Error Alignerror Flag Code Error Codeerror FlagCRC Error Crcerror Flag Jabber FlagInternal Memory Emac Control ModuleBus Arbiter CPUInterrupt Control Transmit Pulse InterruptReceive Pulse Interrupt Receive Threshold Pulse Interrupt Miscellaneous Pulse InterruptInterrupt Pacing Mdio Module Components Mdio ModuleMdio Clock Generator Global PHY Detection and Link State MonitoringPHY Register User Access Active PHY MonitoringMdio Module Operational Overview Initializing the Mdio Module Writing Data To a PHY RegisterReading Data From a PHY Register Example 3. Mdio Register Access Macros Example of Mdio Register Access CodeEmac Module Components Emac ModuleReceive DMA Engine Receive FifoMAC Receiver Clock and Reset LogicReceive Address Transmit DMA EngineEmac Module Operational Overview Data Reception Media Independent Interface MIIReceive Control Receive Inter-Frame IntervalIeee 802.3x-Based Receive Buffer Flow Control Collision-Based Receive Buffer Flow ControlCRC Insertion Transmit ControlAdaptive Performance Optimization APO Interpacket-Gap IPG EnforcementSpeed, Duplex, and Pause Frame Support Transmit Flow ControlReceive DMA Host Configuration Packet Receive OperationReceive Channel Enabling Hardware Receive QOS Support Receive Address MatchingHost Free Buffer Tracking Receive Channel TeardownReceive Frame Classification Promiscuous Receive Mode Receive Frame Treatment SummaryReceive Frame Treatment Receive Overrun Middle of Frame Overrun TreatmentMiddle of Frame Overrun Treatment Packet Transmit Operation Transmit DMA Host ConfigurationReceive and Transmit Latency Transmit Channel TeardownReset Considerations Software Reset ConsiderationsTransfer Node Priority Initialization Hardware Reset ConsiderationsEnabling the EMAC/MDIO Peripheral Emac Control Module InitializationExample 4. Emac Control Module Initialization Code Example 5. Mdio Module Initialization Code Mdio Module InitializationEmac Module Initialization Emac Module Interrupt Events and Requests Interrupt SupportReceive Threshold Interrupts Transmit Packet Completion InterruptsReceive Packet Completion Interrupts Statistics Interrupt Host Error InterruptMdio Module Interrupt Events and Requests User Access Completion InterruptLink Change Interrupt Proper Interrupt ProcessingEmulation Considerations Power ManagementEmulation Control Soft Free DescriptionSlave Vbus Emac Control Module RegistersAcronym Register Description Bit Field Value DescriptionSoftreset Emac Control Module Software Reset Register CmsoftresetEmac Control Module Emulation Control Register Cmemcontrol Soft FreeEmac Control Module Interrupt Control Register Cmintctrl IntpaceenIntprescale Rxpulseen RxthreshenTxpulseen Statpendinten Hostpendinten Linkinten Userinten Bit FieldStatpendinten Rxpulseinttstat Rxthreshinttstat31-8 Reserved TXPULSEINTTSTATn TxpulseinttstatStatpendintstat Statpendintstat Hostpendintstat Linkintstat UserintstatTximax RximaxMdio Version Register Version Management Data Input/Output Mdio RegistersMdio Version Register Version Field Descriptions Mdio Control Register Control Field Descriptions Mdio Control Register ControlPHY Link Status Register Link PHY Acknowledge Status Register AlivePHY Acknowledge Status Register Alive Field Descriptions PHY Link Status Register Link Field Descriptions31-2 Reserved Will clear the event and writing a 0 has no effect No Mdio user command complete event USERINTMASKED0 and USERINTMASKED1 correspond to USERACCESS0 W1S-0 Mdio User Command Complete Interrupt Mask Clear Register Mdio User Command Complete Interrupt Mask Clear RegisterMdio User Access Register 0 USERACCESS0 Field Descriptions Mdio User Access Register 0 USERACCESS0Linksel Linkintenb Mdio User PHY Select Register 0 USERPHYSEL0Phyadrmon LinkselMdio User Access Register 1 USERACCESS1 Field Descriptions Mdio User Access Register 1 USERACCESS1Mdio User PHY Select Register 1 USERPHYSEL1 Mdio User PHY Select Register 1 USERPHYSEL1Ethernet Media Access Controller Emac Registers Offset Acronym Register Description Network Statistics Registers Transmit Identification and Version Register Txidver Transmit Control Register TxcontrolTransmit Control Register Txcontrol Field Descriptions Transmit Teardown Register Txteardown Transmit Teardown Register Txteardown Field DescriptionsTxtdnch Rxident Receive Identification and Version Register RxidverRxmajorver Rxminorver RxmajorverReceive Teardown Register Rxteardown Receive Control Register RxcontrolReceive Control Register Rxcontrol Field Descriptions Receive Teardown Register Rxteardown Field DescriptionsTX7PEND Transmit Interrupt Status Unmasked Register TxintstatrawTransmit Interrupt Status Masked Register Txintstatmasked Transmit Interrupt Status Masked Register TxintstatmaskedTX7MASK Transmit Interrupt Mask Set Register TxintmasksetTransmit Interrupt Mask Clear Register Txintmaskclear Transmit Interrupt Mask Clear Register TxintmaskclearMAC End Of Interrupt Vector Register Maceoivector MAC Input Vector Register MacinvectorMAC Input Vector Register Macinvector Field Descriptions StatpendRX7PEND Receive Interrupt Status Unmasked Register RxintstatrawReceive Interrupt Status Masked Register Rxintstatmasked Receive Interrupt Status Masked Register RxintstatmaskedRX7MASK Receive Interrupt Mask Set Register RxintmasksetReceive Interrupt Mask Clear Register Rxintmaskclear Receive Interrupt Mask Clear Register RxintmaskclearMAC Interrupt Status Unmasked Register Macintstatraw MAC Interrupt Status Masked Register MacintstatmaskedHostpend Statpend MAC Interrupt Mask Clear Register Macintmaskclear MAC Interrupt Mask Set Register MacintmasksetHostmask Statmask HostmaskRxcmfen Rxpasscrc Rxqosen RxnochainRxcsfen Rxcefen Rxcafen RxpromchFrames containing errors are filtered Receive multicast channel select RXCH7EN Receive Unicast Enable Set Register RxunicastsetReceive 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 Receive Channel 0-7 Free Buffer Count Register RXnFREEBUFFER MAC Control Register Maccontrol Field Descriptions MAC Control Register MaccontrolRxbufferflowen TxflowenLoopback FullduplexMAC Status Register Macstatus Field Descriptions MAC Status Register MacstatusRxqosact Fifo Control Register Fifocontrol Emulation Control Register EmcontrolEmulation Control Register Emcontrol Field Descriptions Fifo Control Register Fifocontrol Field DescriptionsSoft Reset Register Softreset MAC Configuration Register MacconfigMAC Configuration Register Macconfig Field Descriptions Soft Reset Register Softreset Field DescriptionsMAC Source Address High Bytes Register Macsrcaddrhi MAC Source Address Low Bytes Register MacsrcaddrloMAC Hash Address Register 2 MACHASH2 MAC Hash Address Register 1 MACHASH1MAC Hash Address Register 1 MACHASH1 Field Descriptions MAC Hash Address Register 2 MACHASH2 Field DescriptionsBack Off Test Register Bofftest Transmit Pacing Algorithm Test Register TpacetestBack Off Test Register Bofftest Field Descriptions Transmit Pause Timer Register Txpause Receive Pause Timer Register RxpauseReceive Pause Timer Register Rxpause Field Descriptions Transmit Pause Timer Register Txpause Field DescriptionsMAC Address Low Bytes Register Macaddrlo Field Descriptions MAC Address Low Bytes Register MacaddrloValid Matchfilt Channel MACADDR0 MACADDR1 ValidMAC Index Register Macindex MAC Address High Bytes Register MacaddrhiMAC Index Register Macindex Field Descriptions MACADDR2 MACADDR3 MACADDR4 MACADDR5TXnHDP Receive Channel 0-7 Completion Pointer Register RXnCP Transmit Channel 0-7 Completion Pointer Register TXnCPGood Receive Frames Register Rxgoodframes Network Statistics RegistersBroadcast Receive Frames Register Rxbcastframes Multicast Receive Frames Register RxmcastframesReceive Alignment/Code Errors Register Rxaligncodeerrors Receive CRC Errors Register RxcrcerrorsPause Receive Frames Register Rxpauseframes Receive Oversized Frames Register RxoversizedReceive Undersized Frames Register Rxundersized Receive Jabber Frames Register RxjabberReceive Frame Fragments Register Rxfragments Filtered Receive Frames Register RxfilteredReceive Octet Frames Register Rxoctets Receive QOS Filtered Frames Register RxqosfilteredGood Transmit Frames Register Txgoodframes Broadcast Transmit Frames Register TxbcastframesDeferred Transmit Frames Register Txdeferred Pause Transmit Frames Register TxpauseframesTransmit Collision Frames Register Txcollision Transmit Single Collision Frames Register TxsinglecollTransmit Carrier Sense Errors Register Txcarriersense Transmit Underrun Error Register TxunderrunTransmit Late Collision Frames Register Txlatecoll Transmit Octet Frames Register TxoctetsSubmit Documentation Feedback Receive DMA Overruns Register Rxdmaoverruns Network Octet Frames Register NetoctetsAppendix a Glossary Term Definition Physical Layer DefinitionsReference Additions/Modifications/Deletions Document Revision HistoryProducts Applications DSPRfid
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