Texas Instruments TMS320DM36X manual Next Descriptor Pointer, Buffer Pointer, Buffer Offset

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2.6.4.1Next Descriptor Pointer

The next descriptor pointer points to the 32-bit word aligned memory address of the next buffer descriptor in the transmit queue. This pointer is used to create a linked list of buffer descriptors. If the value of this pointer is zero, then the current buffer is the last buffer in the queue. The software application must set this value prior to adding the descriptor to the active transmit list. This pointer is not altered by the EMAC.

The value of pNext should never be altered once the descriptor is in an active transmit queue, unless its current value is NULL. If the pNext pointer is initially NULL, and more packets need to be queued for transmit, the software application may alter this pointer to point to a newly appended descriptor. The EMAC will use the new pointer value and proceed to the next descriptor unless the pNext value has already been read. In this latter case, the transmitter will halt on the transmit channel in question, and the software application may restart it at that time. The software can detect this case by checking for an end of queue (EOQ) condition flag on the updated packet descriptor when it is returned by the EMAC.

2.6.4.2Buffer Pointer

The buffer pointer is the byte-aligned memory address of the memory buffer associated with the buffer descriptor. The software application must set this value prior to adding the descriptor to the active transmit list. This pointer is not altered by the EMAC.

2.6.4.3Buffer Offset

This 16-bit field indicates how many unused bytes are at the start of the buffer. For example, a value of 0000h indicates that no unused bytes are at the start of the buffer and that valid data begins on the first byte of the buffer, while a value of 000Fh indicates that the first 15 bytes of the buffer are to be ignored by the EMAC and that valid buffer data starts on byte 16 of the buffer. The software application must set this value prior to adding the descriptor to the active transmit list. This field is not altered by the EMAC.

Note that this value is only checked on the first descriptor of a given packet (where the start of packet (SOP) flag is set). It can not be used to specify the offset of subsequent packet fragments. Also, since the buffer pointer may point to any byte–aligned address, this field may be entirely superfluous, depending on the device driver architecture.

The range of legal values for this field is 0 to (Buffer Length – 1).

2.6.4.4Buffer Length

This 16-bit field indicates how many valid data bytes are in the buffer. On single fragment packets, this value is also the total length of the packet data to be transmitted. If the buffer offset field is used, the offset bytes are not counted as part of this length. This length counts only valid data bytes. The software application must set this value prior to adding the descriptor to the active transmit list. This field is not altered by the EMAC.

2.6.4.5Packet Length

This 16-bit field specifies the number of data bytes in the entire packet. Any leading buffer offset bytes are not included. The sum of the buffer length fields of each of the packet’s fragments (if more than one) must be equal to the packet length. The software application must set this value prior to adding the descriptor to the active transmit list. This field is not altered by the EMAC. This value is only checked on the first descriptor of a given packet (where the start of packet (SOP) flag is set).

2.6.4.6Start of Packet (SOP) Flag

When set, this flag indicates that the descriptor points to a packet buffer that is the start of a new packet. In the case of a single fragment packet, both the SOP and end of packet (EOP) flags are set. Otherwise, the descriptor pointing to the last packet buffer for the packet sets the EOP flag. This bit is set by the software application and is not altered by the EMAC.

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

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Contents Users Guide Submit Documentation Feedback Mdio Registers Mdio Version Register Version Mdio Control Register Control Appendix a Appendix BList 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 Features Purpose of the PeripheralFunctional Block Diagram Emac and Mdio 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 Protocol Overview Ethernet Frame FormatEthernet Frame Description Field Bytes DescriptionEthernet’s Multiple Access Protocol Programming InterfacePacket Buffer Descriptors WordBasic Descriptor Description Field Field DescriptionTransmit and Receive Descriptor Queues Transmit and Receive Emac Interrupts Transmit Buffer Descriptor Format Example 1. Transmit Buffer Descriptor in C Structure FormatNext Descriptor Pointer Buffer PointerBuffer Offset Buffer LengthEnd of Packet EOP Flag Ownership Owner 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 Code Error Codeerror Flag Alignment Error Alignerror FlagCRC Error Crcerror Flag Jabber FlagEmac Control Module Internal MemoryBus Arbiter CPUInterrupt Control Transmit Pulse InterruptReceive Pulse Interrupt Receive Threshold Pulse Interrupt Miscellaneous Pulse InterruptInterrupt Pacing Mdio Module Mdio Module ComponentsMdio 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 of Mdio Register Access Code Example 3. Mdio Register Access MacrosEmac Module Emac Module ComponentsReceive DMA Engine Receive FifoClock and Reset Logic MAC ReceiverReceive Address Transmit DMA EngineEmac Module Operational Overview Media Independent Interface MII Data ReceptionReceive Control Receive Inter-Frame IntervalCollision-Based Receive Buffer Flow Control Ieee 802.3x-Based Receive Buffer Flow ControlTransmit Control CRC InsertionAdaptive Performance Optimization APO Interpacket-Gap IPG EnforcementTransmit Flow Control Speed, Duplex, and Pause Frame SupportReceive DMA Host Configuration Packet Receive OperationReceive Channel Enabling Receive Address Matching Hardware Receive QOS SupportHost 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 Transmit DMA Host Configuration Packet Transmit OperationReceive and Transmit Latency Transmit Channel TeardownReset Considerations Software Reset ConsiderationsTransfer Node Priority Hardware Reset Considerations InitializationEnabling the EMAC/MDIO Peripheral Emac Control Module InitializationExample 4. Emac Control Module Initialization Code Mdio Module Initialization Example 5. Mdio Module Initialization CodeEmac Module Initialization Interrupt Support Emac Module Interrupt Events and RequestsReceive Threshold Interrupts Transmit Packet Completion InterruptsReceive Packet Completion Interrupts Host Error Interrupt Statistics InterruptUser Access Completion Interrupt Mdio Module Interrupt Events and RequestsLink Change Interrupt Proper Interrupt ProcessingPower Management Emulation ConsiderationsEmulation Control Soft Free DescriptionEmac Control Module Registers Slave VbusAcronym Register Description Bit Field Value DescriptionEmac Control Module Software Reset Register Cmsoftreset SoftresetEmac Control Module Emulation Control Register Cmemcontrol Soft FreeEmac Control Module Interrupt Control Register Cmintctrl IntpaceenIntprescale Rxthreshen RxpulseenTxpulseen Statpendinten Hostpendinten Linkinten Userinten Bit FieldStatpendinten Rxthreshinttstat RxpulseinttstatTxpulseinttstat 31-8 Reserved TXPULSEINTTSTATnStatpendintstat Hostpendintstat Linkintstat Userintstat StatpendintstatRximax TximaxMdio 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 PHY Link Status Register LinkPHY 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 Mdio User Access Register 0 USERACCESS0 Field DescriptionsMdio User PHY Select Register 0 USERPHYSEL0 Linksel LinkintenbPhyadrmon LinkselMdio 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 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 Receive Identification and Version Register Rxidver RxidentRxmajorver Rxminorver RxmajorverReceive Control Register Rxcontrol Receive Teardown Register RxteardownReceive Control Register Rxcontrol Field Descriptions Receive Teardown Register Rxteardown Field DescriptionsTransmit 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 TxintmaskclearMAC Input Vector Register Macinvector MAC End Of Interrupt Vector Register MaceoivectorMAC Input Vector Register Macinvector Field Descriptions StatpendReceive 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 MAC Interrupt Mask Set Register Macintmaskset MAC Interrupt Mask Clear Register MacintmaskclearHostmask Statmask HostmaskRxpasscrc Rxqosen Rxnochain RxcmfenRxcsfen Rxcefen Rxcafen 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 Receive Channel 0-7 Free Buffer Count Register RXnFREEBUFFER MAC Control Register Maccontrol MAC Control Register Maccontrol Field DescriptionsTxflowen RxbufferflowenLoopback FullduplexMAC Status Register Macstatus MAC Status Register Macstatus Field DescriptionsRxqosact Emulation Control Register Emcontrol Fifo Control Register FifocontrolEmulation Control Register Emcontrol Field Descriptions Fifo Control Register Fifocontrol Field DescriptionsMAC Configuration Register Macconfig Soft Reset Register SoftresetMAC Configuration Register Macconfig Field Descriptions Soft Reset Register Softreset Field DescriptionsMAC Source Address Low Bytes Register Macsrcaddrlo MAC Source Address High Bytes Register MacsrcaddrhiMAC Hash Address Register 1 MACHASH1 MAC Hash Address Register 2 MACHASH2MAC 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 Receive Pause Timer Register Rxpause Transmit Pause Timer Register TxpauseReceive Pause Timer Register Rxpause Field Descriptions Transmit Pause Timer Register Txpause Field DescriptionsMAC Address Low Bytes Register Macaddrlo MAC Address Low Bytes Register Macaddrlo Field DescriptionsValid Matchfilt Channel MACADDR0 MACADDR1 ValidMAC Address High Bytes Register Macaddrhi MAC Index Register MacindexMAC Index Register Macindex Field Descriptions MACADDR2 MACADDR3 MACADDR4 MACADDR5TXnHDP Transmit Channel 0-7 Completion Pointer Register TXnCP Receive Channel 0-7 Completion Pointer Register RXnCPNetwork Statistics Registers Good Receive Frames Register RxgoodframesBroadcast Receive Frames Register Rxbcastframes Multicast Receive Frames Register RxmcastframesReceive CRC Errors Register Rxcrcerrors Receive Alignment/Code Errors Register RxaligncodeerrorsPause Receive Frames Register Rxpauseframes Receive Oversized Frames Register RxoversizedReceive Jabber Frames Register Rxjabber Receive Undersized Frames Register RxundersizedReceive Frame Fragments Register Rxfragments Filtered Receive Frames Register RxfilteredReceive QOS Filtered Frames Register Rxqosfiltered Receive Octet Frames Register RxoctetsGood Transmit Frames Register Txgoodframes Broadcast Transmit Frames Register TxbcastframesPause Transmit Frames Register Txpauseframes Deferred Transmit Frames Register TxdeferredTransmit Collision Frames Register Txcollision Transmit Single Collision Frames Register TxsinglecollTransmit Underrun Error Register Txunderrun Transmit Carrier Sense Errors Register TxcarriersenseTransmit Late Collision Frames Register Txlatecoll Transmit Octet Frames Register TxoctetsSubmit Documentation Feedback Network Octet Frames Register Netoctets Receive DMA Overruns Register RxdmaoverrunsAppendix a Glossary Physical Layer Definitions Term DefinitionDocument Revision History Reference Additions/Modifications/DeletionsProducts Applications DSPRfid
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