Texas Instruments TNETX4090 Adaptive performance optimization APO, Interframe gap enforcement

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TNETX4090

ThunderSWITCH II9-PORT 100-/1000-MBIT/S ETHERNETSWITCH

SPWS044E ± DECEMBER 1997 ± REVISED AUGUST 1999

adaptive performance optimization (APO)

Each Ethernet MAC incorporates APO logic. This can be enabled on an individual port basis. When enabled, the MAC uses transmission pacing to enhance performance (when connected on networks using other transmit pacing-capable MACs). Adaptive performance pacing introduces delays into the normal transmission of frames, delaying transmission attempts between stations, reducing the probability of collisions occurring during heavy traffic (as indicated by frame deferrals and collisions), thereby, increasing the chance of successful transmission.

When a frame is deferred, suffers a single collision, multiple collisions, or excessive collisions, the pacing counter is loaded with an initial value of 31. When a frame is transmitted successfully (without a deferral, single collision, multiple collision, or excessive collision), the pacing counter is decremented by 1, down to 0.

With pacing enabled, a new frame is permitted to immediately [after one inter-packet gap (IPG)] attempt transmission only if the pacing counter is 0. If the pacing counter is not 0, the frame is delayed by the pacing delay (a delay of approximately four interframe gap delays).

NOTE:

APO affects only the IPG preceding the first attempt at transmitting a frame. It does not affect the backoff algorithm for retransmitted frames.

interframe gap enforcement

The measurement reference for the interpacket gap of 96-bit times is changed, depending on frame traffic conditions. If a frame is successfully transmitted (without collision), 96-bit times is measured from Mxx_TXEN. If the frame suffered a collision, 96-bit times is measured from Mxx_CRS.

backoff

The device implements the IEEE Std 802.3 binary exponential backoff algorithm.

receive versus transmit priority

The queue manager prioritizes receive and transmit traffic as follows:

DHighest priority is given to frames that currently are being transmitted. This ensures that transmitting frames do not underrun.

DNext priority is given to frames that are received if the free-buffer stack is not empty. This ensures that received frames are not dropped unless it is impossible to receive them.

DLowest priority is given to frames that are queued for transmission but have not yet started to transmit. These frames are promoted to the highest priority only when there is spare capacity on the memory bus.

DThe NM port receives the lowest priority to prevent frame loss during busy periods.

The memory bus has enough bandwidth to support the two highest priorities. The untransmitted frame queues grow when frames received on different ports require transmission on the same port(s) and when frames are repeatedly received on ports that are at a higher speed than the ports on which they are transmitted. This is likely to be exacerbated by the reception of multicast frames, which typically require transmission on several ports. When the backlog grows to such an extent that the free buffer stack is nearly empty, flow control is initiated (if it has been enabled) to limit further frame reception.

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Contents Description MAC MII MIIMAC Eeprom CPU I/F DMAPCS Duplex LED Rdram Interface Jtag Interface GGP Package Bottom View Signal Ball Name Signal-to-Ball Mapping Signal Names Sorted AlphabeticallyReset Sdma SAD0 Jtag interface Terminal FunctionsControl logic interface Terminal Internal Description Name RESISTOR²M08TXD7 M08TXD6 M08TXD5 100-/1000-Mbit/s MAC interface Gmii modeTerminal Internal Description Name Resistor Port to not support pause frames Pulldown 10-/100-Mbit/s MAC interface MII mode ports 0±7M00RENEG M01RENEG M04TCLK M05TCLK M06TCLK M07TCLK AD4 ThunderSWITCH II 9-PORT 100-/1000-MBIT/S ETHERNET SwitchMII management interface Rdram interface Eeprom interface DIO interfacePower supply LED interface100-/1000-Mbit/s port PCS LED interface DIO interface description DIO Internal Register Address MapByte DIO Address TNETX4090 ThunderSWITCH II 9-PORT 100-/1000-MBIT/S ETHERNETVLAN1QID VLAN0QID VLAN37QID VLAN36QID TNETX4090 PCS8Status PCS8Control 0x0700 DIO interface description Port Statistics TailPort no Head Statistic Even ODD Ports 0x90Ex Port no Head Statistic TailSignal Description DMA Interface SignalsAddress-Lookup Statistics Receiving/transmitting management framesDIO Interface During Hardware Reset State of DIO signal terminals during hardware resetDIO Interface State During Hardware Reset Ieee Std 802.1Q Vlan tags on the NM portFCS Vlan IDTpid TCI CRCTNETX4090 Full-duplex NM port PHY management interfaceNM bandwidth and priority Interrupt processingMAC interface Interframe gap enforcement Adaptive performance optimization APOBackoff Receive versus transmit prioritySpeed, duplex, and flow-control negotiation 10-/100-Mbit/s MII ports 0±7100-Mbit/s Port Negotiation With the TNETE2104 100-/1000-Mbit/s PHY interface port Port 8 Pause Negotiation in MII Mode Port 8 Duplex Negotiation in MII ModeFull-duplex hardware flow control OutcomePretagging and extended port awareness Pretag on transmissionM08GTCLK M08TXEN Pretag on reception Transmit Pretag Bit DefinitionsLearning Format Receive Pretag Bit Definitions BIT Name FunctionRing-cascade topology Directed Format Receive Pretag Bit DefinitionsRXD Flow COL TXD TNETX4090 RXD Flow COL TXDSwitch Terminal Ring-Topology ConnectivityM08GTCLK M08TXEN M08RXDV SCL SDA Edio TNETX4090 EclkGND Outcome Stop Load Initd ² Fault LED Eclk Interaction of Eeprom load with the SIO registerSummary of Eeprom load outcomes Port LED States Compatibility with future device revisionsCollision LED States State DisplayLED Status Bit Definitions and Shift Order PCS duplex LEDLamp test Multi-LED displayBUS Enable GND Rdram BUS Ctrl SIN BUS Enable GND BUS Ctrl Rdram SINTNETX4090 VCC NC Txclk Vref Rxclk VDD Sout SCHAIN0 Txclk Vref Rxclk VDDHighz instruction Jtag Instruction OpcodesRacbist instruction Jtag Bist StatusFrame routing Vlan supportIale Ieee Std 802.1Q tags ± reception Address maintenanceIeee Std 802.1Q header ± transmission Spanning-tree supportAging algorithms Frame-Routing Algorithm SPWS044E ± December 1997 ± Revised August Port routing code Removal of source port Port trunking/load sharingTrunk Group 0 Port Membership Trunk0Ports Register Port trunking exampleTrunk Group 1 Port Membership Trunk1Ports Register Extended port awarenessFlow control Hardware flow control Other flow-control mechanismsMulticast limit System test capabilitiesInternal wrap test Reading RdramPHY TNETX4090 Duplex wrap testMIN NOM MAX Unit Recommended operating conditionsJtag interface Control signals Reset see FigureTiming requirements over recommended operating conditions PMA receive see Figure Physical medium attachment interface port ReceivePMA transmit see Figure TransmitGmii port Gmii receive see FigureGmii transmit see Figure Gmii Clock PMA and Gmii clock see FigureMII receive see Figure MII ports 0±8MII clock see Figure MII transmit see FigureRdram see Figure Rdram interfaceDtxclk Drxclk Dbusctrl DbusenDIO interface DIO and DMA writes see FigureSCS Srnw SAD1±SAD0 Sdma SDATA7± SDATA0 Srdy Sint SCS Srnw SAD1±SAD0 Sdma SDATA7± SDATA0 Srdy DIO and DMA reads see FigureEeprom interface Eeprom writes see FigureEeprom reads see Figure LED interface LED see FigureLedclk Leddata VOL VOHTTL Output Macro Propagation-Delay-Time Voltage Waveforms VDD VOH 50% LvcmosVOL VDD Mechanical Data TBD TNETX4090GGP Obsolete BGAImportant Notice
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