Xilinx UG194 Virtex-5 FPGA Embedded Tri-Mode Ethernet MAC ...

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Chapter 3: Client Interface Requirement for Flow Control Figure 3-27 illustrates the requirement for flow control. The Ethernet MAC on the right side of the figure has a reference clock slightly faster than the nominal 125 MHz. The Ethernet MAC on the left side of the figure has a reference clock slightly slower than the nominal 125 MHz. This results in the Ethernet MAC on the left side of the figure not being able to match the full line rate of the Ethernet MAC on the right side (due to clock tolerances). The left Ethernet MAC is illustrated as performing a loopback implementation; this results in the FIFO filling up over time. Without flow control, this FIFO eventually fills and overflows, resulting in the corruption or loss of Ethernet frames. Application Flow Control Basics Client Logic FIFO Figure 3-27: Requirement for Flow Control An Ethernet MAC transmits a pause control frame for the link partner to cease transmission for a defined period of time. For example, the left Ethernet MAC of Figure 3-27 initiates a pause request when the client FIFO (illustrated) reaches a nearly full state. An Ethernet MAC responds to received pause control frames by ceasing transmission of frames for the period of time defined in the received pause control frame. For example, the right Ethernet MAC of Figure 3-27 ceases transmission after receiving the pause control frame transmitted by the left Ethernet MAC. In a well-designed system, the right Ethernet MAC ceases transmission before the client FIFO of the left Ethernet MAC overflows. This provides time to empty the FIFO to a safe level before normal operation resumes. It also safeguards the system against FIFO overflow conditions and frame loss. 74 www.xilinx.com TEMAC User Guide UG194 (v1.10) February 14, 2011 MAC TX RX 125 MHz –100 ppm 125 MHz +100 ppm MAC RX TX UG194_3_27_072606 R
R Transmitting a PAUSE Control Frame Flow Control Block The client initiates a flow control frame by asserting CLIENTEMAC#PAUSEREQ when the pause value is on the CLIENTEMAC#PAUSEVAL[15:0] bus. When the optional clock enables are not used, these signals are synchronous to CLIENTEMAC#TXCLIENTCLKIN. The timing is shown in Figure 3-28. CLIENTEMAC#TXCLIENTCLKIN CLIENTEMAC#PAUSEVAL[15:0] When the optional clock enable clocking scheme is used, the signals are synchronous to PHYEMAC#TXGMIIMIICLKIN. These signals are written into the Ethernet MAC when the enable signal, EMAC#CLIENTTXCLIENTCLKOUT, is High. When the Ethernet MAC is configured to support transmit flow control, a PAUSE control frame is transmitted on the link. When CLIENTEMAC#PAUSEREQ is asserted, the PAUSE parameter is set to the CLIENTEMAC#PAUSEVAL[15:0] value. This does not disrupt any frame transmission in progress, but it takes priority over any pending frame transmission. The PAUSE control frame is transmitted even if the transmitter is in a paused state. An example of a PAUSE frame (not drawn to scale) is shown in Figure 3-29. Pause Destination Address 01-80-C2-00-00-01 CLIENTEMAC#PAUSEREQ The pause source address can be configured using the “Configuration Registers,” page 88. The pause time transmitted in the PAUSE frame is the current sampled CLIENTEMAC#PAUSEVAL[15:0] value. Because only a single pause control frame request is stored by the transmitter, if CLIENTEMAC#PAUSEREQ is asserted multiple times prior to the transmission of a control pause frame (i.e., while the previous frame transmission is still in progress), only a single pause frame is transmitted. Receiving a PAUSE Control Frame Figure 3-28: Pause Request Timing Source Address MAC Control Type 0x8808 64-Byte Data Field MAC Control OPCODE 0x0001 Figure 3-29: Pause Frame Example UG194_3_28_072106 When an error-free frame is received by the Ethernet MAC, it examines the following information: TEMAC User Guide www.xilinx.com 75 UG194 (v1.10) February 14, 2011 Pause Time 46-Byte Data Field FCS UG194_3_29_072106
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Virtex-5 FPGA Embedded Tri-Mode Eth
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Date Version Revision 08/08/07 (con
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Date Version Revision 10/01/09 1.9
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Table of Contents Guide Contents .
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R Chapter 5: MDIO Interface Introdu
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R About This Guide Guide Contents P
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R Additional Support Resources User
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R Typographical Online Document Use
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Introduction Key Features R Chapter
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R Typical Ethernet Application Over
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R Number of Bytes Physical Sublayer
Page 23 and 24: R Data Pad FCS Ethernet Protocol Ov
Page 25 and 26: R Using the Embedded Ethernet MAC T
Page 27 and 28: R Ethernet MAC Overview Chapter 2 T
Page 29 and 30: Generic Host Bus DCR Bus R Flow Con
Page 31 and 32: R Ethernet MAC Primitive Ethernet M
Page 33 and 34: R Ethernet MAC Signal Descriptions
Page 35 and 36: R Table 2-3: Receive Client Interfa
Page 37 and 38: R DCR Bus Signals Table 2-6: DCR Bu
Page 39 and 40: R Table 2-8: PHY Data and Control S
Page 41 and 42: R Table 2-12: PCS/PMA Signals Table
Page 43 and 44: R Table 2-16: Mode Configuration At
Page 45 and 46: R Table 2-17: MAC Configuration Att
Page 47 and 48: R Table 2-17: MAC Configuration Att
Page 49 and 50: R Table 2-18: Physical Interface At
Page 51 and 52: R Client Interface Chapter 3 This c
Page 53 and 54: R Normal Frame Transmission CLIENTE
Page 55 and 56: R CLIENTEMAC#TXCLIENTCLKIN CLIENTEM
Page 57 and 58: R CLIENTEMAC#TXCLIENTCLKIN CLIENTEM
Page 59 and 60: R Normal Frame Transmission PHYEMAC
Page 61 and 62: R CLIENTEMAC#TXCLIENTCLKIN PHYEMAC#
Page 63 and 64: R CLIENTEMAC#TXCLIENTCLKIN PHYEMAC#
Page 65 and 66: R Frame Reception with Errors CLIEN
Page 67 and 68: R Receive (RX) Client: 8-Bit Interf
Page 69 and 70: R Receive (RX) Client: 16-Bit Inter
Page 71 and 72: R Address Filtering Address Filteri
Page 73: R CLIENTEMAC#RXCLIENTCLKIN Flow Con
Page 77 and 78: R Operation Figure 3-30 illustrates
Page 79 and 80: R Ethernet MAC Block EMAC#CLIENTTXS
Page 81 and 82: R Table 3-3: Bit Definitions for th
Page 83 and 84: R CLIENTEMAC#RXCLIENTCLKIN EMAC#CLI
Page 85 and 86: R Host/DCR Bus Interfaces This chap
Page 87 and 88: HOSTCLK HOSTMIIMSEL HOSTREQ HOSTOPC
Page 89 and 90: R Table 4-3: Receiver Configuration
Page 91 and 92: R Table 4-5: Flow Control Configura
Page 93 and 94: R Table 4-7: RGMII/SGMII Configurat
Page 95 and 96: R Table 4-9: Unicast Address (Word
Page 97 and 98: R Table 4-13: Address Filter Mode 0
Page 99 and 100: R HOSTCLK HOSTMIIMSEL HOSTOPCODE[1]
Page 101 and 102: R HOSTCLK HOSTMIIMSEL HOSTREQ HOSTO
Page 103 and 104: R Using the DCR Bus The directly ad
Page 105 and 106: R Table 4-18: DCR Control Register
Page 107 and 108: R Using the DCR Bus The IRENABLE_e#
Page 109 and 110: R // Write to the cntlReg_e1 regist
Page 111 and 112: DCR Offset 0x1 MSB R Using the DCR
Page 113 and 114: R Using the DCR Bus // EMAC Managem
Page 115 and 116: R MDIO Interface Chapter 5 This cha
Page 117 and 118: MDC MDIO R MDIO Transactions Introd
Page 119 and 120: R MDIO Implementation in the Ethern
Page 121 and 122: Generic Host Bus DCR Bus R PHYEMAC#
Page 123 and 124: R 1000BASE-X PCS/PMA Management Reg
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R Table 5-4: Status Register (Regis
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R 1000BASE-X PCS/PMA Management Reg
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R Table 5-13: Vendor-Specific Regis
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R 2, 3 “PHY Identifier (Registers
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1.2 SGMII Link Status R Table 5-16:
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R Table 5-22: SGMII Auto-Negotiatio
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R Physical Interface Chapter 6 This
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R GMII / MII RGMII SGMII Introducti
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TX CLIENT LOGIC RX CLIENT LOGIC R M
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R Gigabit Media Independent Interfa
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GTX_CLK R IBUFG TX CLIENT LOGIC RX
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GTX_CLK R IBUFG BUFG TX Client Logi
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R Reduced Gigabit Media Independent
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GTX_CLK TX Client Logic RX Client L
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GTX_CLK TX Client Logic RX Client L
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FPGA R PCS/PMA Sublayer MAC TX Inte
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R Ethernet MAC to RocketIO Serial T
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TX and RX Client Logic R 1000BASE-X
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R 1000BASE-X PCS/PMA REFCLKOUT outp
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R DCM BUFG CLKFB CLK0 CLKIN CLKFX B
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R 1000BASE-X PCS/PMA IEEE Std 802.3
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R 1000BASE-X PCS/PMA Ethernet MAC.
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FPGA R Introduction to the SGMII Im
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R RX Elastic Buffer Implementations
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R Serial Gigabit Media Independent
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R Ethernet MAC (PCS/PMA Sublayer) E
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TX and RX Client Logic R SGMII Cloc
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DCM CLKFB CLK0 CLKIN CLKDV CLKDV_DI
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R Interfacing to a Statistics Block
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R Using the DCR Bus to Access Stati
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R Pinout Guidelines Appendix A Xili
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R Ethernet MAC Clocks Appendix B Th
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TX Client Logic RX Client Logic R
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R Clock Enables Clock Connections t
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R Receiver Clock Clock Definitions
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R GMII (Byte PHY) Mode Clock Defini
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R Clock Definitions and Frequencies
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R Virtex-4 to Virtex-5 FPGA Enhance
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R Clock Enables Modifications Relat
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R Additional Attributes Table C-2:
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R Appendix D Differences between So
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