Texas Instruments TMS320DM643X DMP manual Ethernet Protocol Overview, Ethernet Frame Format

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Peripheral Architecture

2.4Ethernet Protocol Overview

A brief overview of the Ethernet protocol is given in the following subsections. For in-depth information on the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method, which is the Ethernet’s multiple access protocol, see the IEEE 802.3 standard document.

2.4.1Ethernet Frame Format

All the Ethernet technologies use the same frame structure. The format of an Ethernet frame is shown in Figure 3 and described in Table 2. The Ethernet packet, which is the collection of bytes representing the data portion of a single Ethernet frame on the wire, is shown outlined in bold. The Ethernet frames are of variable lengths, with no frame smaller than 64 bytes or larger than RXMAXLEN bytes (header, data, and CRC).

Figure 3. Ethernet Frame Format

 

 

 

Number of bytes

 

7

1

6

6

2

46−1500

 

 

 

 

 

 

Preamble

SFD

Destination

Source

Len

Data

 

 

 

 

 

 

Legend: SFD=Start Frame Delimeter; FCS=Frame Check Sequence (CRC)

Table 2. Ethernet Frame Description

4

FCS

Field

Bytes

Description

Preamble

7

Preamble. These 7 bytes have a fixed value of 55h and serve to wake up the receiving

 

 

EMAC ports and to synchronize their clocks to that of the sender’s clock.

SFD

1

Start of Frame Delimiter. This field with a value of 5Dh immediately follows the preamble

 

 

pattern and indicates the start of important data.

Destination

6

Destination address. This field contains the Ethernet MAC address of the EMAC port for

 

 

which the frame is intended. It may be an individual or multicast (including broadcast)

 

 

address. When the destination EMAC port receives an Ethernet frame with a destination

 

 

address that does not match any of its MAC physical addresses, and no promiscuous,

 

 

multicast or broadcast channel is enabled, it discards the frame.

Source

6

Source address. This field contains the MAC address of the Ethernet port that transmits the

 

 

frame to the Local Area Network.

Len

2

Length/Type field. The length field indicates the number of EMAC client data bytes

 

 

contained in the subsequent data field of the frame. This field can also be used to identify

 

 

the type of data the frame is carrying.

Data

46 to

Data field. This field carries the datagram containing the upper layer protocol frame, that is,

 

(RXMAXLEN - 18)

IP layer datagram. The maximum transfer unit (MTU) of Ethernet is (RXMAXLEN - 18)

 

 

bytes. This means that if the upper layer protocol datagram exceeds (RXMAXLEN - 18)

 

 

bytes, then the host has to fragment the datagram and send it in multiple Ethernet packets.

 

 

The minimum size of the data field is 46 bytes. This means that if the upper layer datagram

 

 

is less then 46 bytes, the data field has to be extended to 46 bytes by appending extra bits

 

 

after the data field, but prior to calculating and appending the FCS.

FCS

4

Frame Check Sequence. A cyclic redundancy check (CRC) is used by the transmit and

 

 

receive algorithms to generate a CRC value for the FCS field. The frame check sequence

 

 

covers the 60 to 1514 bytes of the packet data. Note that this 4-byte field may or may not

 

 

be included as part of the packet data, depending on how the EMAC is configured.

SPRU941A –April 2007Ethernet Media Access Controller (EMAC)/ 15

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Management Data Input/Output (MDIO)

 

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Contents Users Guide Submit Documentation Feedback Contents MAC Hash Address Register 1 MACHASH1 Appendix B Appendix aList of Figures Transmit Pacing Algorithm Test Register Tpacetest List of Tables Fifo Control Register Fifocontrol Field Descriptions Read This First Purpose of the Peripheral Features Emac and Mdio Block Diagram Functional Block DiagramMemory Map Signal DescriptionsIndustry Standards Compliance Statement Clock ControlSignal Type Description Emac and Mdio SignalsField Bytes Description Ethernet Protocol OverviewEthernet Frame Format Ethernet Frame DescriptionEthernet’s Multiple Access Protocol Programming InterfacePacket Buffer Descriptors Typical Descriptor Linked List 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 Length Next Descriptor PointerBuffer Pointer Buffer OffsetTeardown Complete Tdowncmplt Flag End of Packet EOP FlagOwnership Owner Flag End of Queue EOQ FlagReceive Buffer Descriptor Format Receive Buffer Descriptor Format#define Emacdscflagjabber Example 2. Receive Buffer Descriptor in C Structure FormatBuffer Length Jabber Flag Code Error Codeerror FlagAlignment Error Alignerror Flag CRC Error Crcerror FlagBus Arbiter Emac Control ModuleNo Match Nomatch Flag Internal MemoryMdio Module Interrupt ControlMdio Module Components Active PHY Monitoring PHY Register User AccessMdio Clock Generator Global PHY Detection and Link State 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 CodeReceive Fifo Emac ModuleEmac Module Components Receive DMA EngineMAC Transmitter Clock and Reset LogicTransmit DMA Engine Transmit FifoReceive Inter-Frame Interval Media Independent Interface MIIData Reception Receive ControlIeee 802.3x-Based Receive Buffer Flow Control Collision-Based Receive Buffer Flow ControlInterpacket-Gap IPG Enforcement Transmit ControlCRC Insertion Adaptive Performance Optimization APOSpeed, Duplex, and Pause Frame Support Transmit Flow ControlReceive Address Matching Receive DMA Host ConfigurationPacket Receive Operation Receive Channel EnablingHardware Receive QOS Support Host Free Buffer TrackingReceive Channel Teardown Receive Frame Classification Promiscuous Receive ModeReceive Frame Treatment Receive Frame Treatment SummaryReceive Overrun Middle of Frame Overrun TreatmentMiddle of Frame Overrun Treatment Transmit Channel Teardown Transmit DMA Host ConfigurationPacket Transmit Operation Receive and Transmit LatencyReset Considerations Software Reset ConsiderationsTransfer Node Priority Emac Control Module Initialization Hardware Reset ConsiderationsInitialization Enabling the EMAC/MDIO PeripheralExample 4. Emac Control Module Initialization Code Mdio Module InitializationExample 5. Mdio Module Initialization Code Emac Module Initialization Receive Packet Completion Interrupts Interrupt SupportEmac Module Interrupt Events and Requests Transmit Packet Completion InterruptsStatistics Interrupt Host Error InterruptProper Interrupt Processing User Access Completion InterruptMdio Module Interrupt Events and Requests Link Change InterruptPower Management Emulation ConsiderationsEmulation Control Bit Field Emac Control Module Interrupt Control Register EwctlEmac Control Module Registers Acronym Register DescriptionEmac 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 Field Descriptions Mdio Control Register ControlPHY Link Status Register Link Field Descriptions PHY Acknowledge Status Register AlivePHY Link Status Register Link PHY Acknowledge Status Register Alive 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 Field Descriptions Mdio User Access Register 0 USERACCESS0Bit Field Value Description Mdio User PHY Select Register 0 USERPHYSEL0Linksel Linkintenb PhyadrmonMdio 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 Ethernet Media Access Controller Emac RegistersNetwork Statistics Registers Offset Acronym Register DescriptionTransmit 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 TX7PEND 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 TxintmaskclearHostpend Statpend Rxpend Txpend MAC Input Vector Register MacinvectorMAC Input Vector Register Macinvector Field Descriptions Userint LinkintRX7PEND 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 Hostmask MAC Interrupt Mask Set Register MacintmasksetMAC Interrupt Mask Clear Register Macintmaskclear Hostmask StatmaskRxpromch Rxpasscrc Rxqosen RxnochainRxcmfen Rxcsfen Rxcefen RxcafenFrames 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 Reserved RX nFLOWTHRESH FFh RxfilterthreshReceive Channel 0-7 Free Buffer Count Register RXnFREEBUFFER MAC Control Register Maccontrol Field Descriptions MAC Control Register MaccontrolLoopback Sent. Full-duplex mode no outgoing pause frames are sentMAC Status Register Macstatus Field Descriptions MAC Status Register MacstatusBit Field Value Description MAC Status Register Macstatus Field DescriptionsFifo Control Register Fifocontrol Field Descriptions Emulation Control Register EmcontrolFifo Control Register Fifocontrol Emulation Control Register Emcontrol Field DescriptionsSoft Reset Register Softreset Field Descriptions MAC Configuration Register MacconfigSoft Reset Register Softreset MAC Configuration Register Macconfig Field DescriptionsMAC Source Address High Bytes Register Macsrcaddrhi MAC Source Address Low Bytes Register MacsrcaddrloMAC Hash Address Register 2 MACHASH2 Field Descriptions MAC Hash Address Register 1 MACHASH1MAC Hash Address Register 2 MACHASH2 MAC Hash Address Register 1 MACHASH1 Field DescriptionsBack Off Test Register Bofftest Transmit Pacing Algorithm Test Register TpacetestBack Off Test Register Bofftest Field Descriptions Transmit Pause Timer Register Txpause Field Descriptions Receive Pause Timer Register RxpauseTransmit Pause Timer Register Txpause Receive Pause Timer Register Rxpause 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 Receive Channel 0-7 Completion Pointer Register RXnCP Transmit Channel 0-7 Completion Pointer Register TXnCPMulticast Receive Frames Register Rxmcastframes Network Statistics RegistersGood Receive Frames Register Rxgoodframes Broadcast Receive Frames Register RxbcastframesReceive Oversized Frames Register Rxoversized Receive CRC Errors Register RxcrcerrorsReceive Alignment/Code Errors Register Rxaligncodeerrors Pause Receive Frames Register RxpauseframesFiltered Receive Frames Register Rxfiltered Receive Jabber Frames Register RxjabberReceive Undersized Frames Register Rxundersized Receive Frame Fragments Register RxfragmentsReceive QOS Filtered Frames Register Rxqosfiltered Receive Octet Frames Register RxoctetsGood Transmit Frames Register Txgoodframes Deferred Transmit Frames Register Txdeferred Broadcast Transmit Frames Register TxbcastframesMulticast Transmit Frames Register Txmcastframes Pause Transmit Frames Register TxpauseframesTransmit Late Collision Frames Register Txlatecoll Transmit Underrun Error Register TxunderrunTransmit Single Collision Frames Register Txsinglecoll Transmit Multiple Collision Frames Register TxmulticollTransmit 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 Term Definition Table A-1. Physical Layer DefinitionsReference Additions/Modifications/Deletions Table B-1. Document Revision HistoryDSP Products Applications
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