-- DISCONTINUED PRODUCT --

Transmitting Outbound Frames

R

VLAN Tagged Frames

Figure 5-9illustrates transmission of a VLAN tagged frame (if enabled). The handshaking signals across the interface do not change; however, the VLAN type tag 81-00 must be supplied by the client to signify that the frame is VLAN tagged. The client also supplies the two bytes of Tag Control Information, V1 and V2, at the appropriate times in the data stream. More information on the contents of these two bytes can be found in IEEE 802.3- 2005. For more information about enabling and disabling jumbo frame handling, see “Configuration Registers,” on page 78.

gtx_clk

tx_data[7:0]

tx_data_valid

tx_ack

tx_underrun

 

 

81 00 V1V2

 

 

DA

SA

VLAN

L/T

DATA

 

 

tag

 

 

Figure 5-9:Transmission of a VLAN Tagged Frame

Maximum Permitted Frame Length

The maximum legal length of a frame specified in IEEE 802.3-2005is 1518 bytes for non- VLAN tagged frames. VLAN tagged frames may be extended to 1522 bytes. When jumbo frame handling is disabled and the client attempts to transmit a frame that exceeds the maximum legal length, the GEMAC core will insert an error code to corrupt the current frame, and the frame will be truncated to the maximum legal length. When jumbo frame handling is enabled, frames longer than the legal maximum are transmitted error-free. For more information on enabling and disabling Jumbo frame handling, see “Configuration Registers,” on page 78.

Inter-Frame Gap Adjustment

A configuration bit in the transmitter control register (see “Configuration Registers,” on page 78) allows you to control the length of the inter-frame gap transmitted by the MAC on the physical interface. If this function is selected, the MAC exerts back pressure on the client interface to delay the transmission of the next frame until the requested number of idle cycles has elapsed. The number of idle cycles is controlled by the value on the tx_ifg_delay port seen at the start of frame transmission on the client interface. Figure 5-10shows the MAC operating in this mode.

Reducing the interframe gap to below the IEEE 802.3-2005minimum of 12 idles is supported, but the MAC will transmit an absolute minimum of 4 idles. If the Ethernet Statistics core is used with the MAC, then accuracy cannot be guaranteed if the interframe gap adjustment is set to less than 12 idles. However, the tx_statistic_vector and rx_statistic_vector values will always remain correct.

1-Gigabit Ethernet MAC v8.5 User Guide

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UG144 April 24, 2009

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Xilinx UG144 manual Inter-Frame Gap Adjustment, 9Transmission of a Vlan Tagged Frame
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UG144 specifications

The Xilinx UG144, a comprehensive user guide for the versatile Zynq-7000 SoC (System on Chip) architecture, serves as an essential resource for developers and engineers designing embedded systems. Emphasizing the blend of programmable logic and processing power, this guide highlights the array of features and technologies that make the Zynq-7000 series particularly attractive for a wide range of applications.

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