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RocketIO Logic with the Fabric Rx Elastic Buffer
R
The core is designed to integrate with the
Note: A small logic shim (included in the block” level wrapper) is required to convert between the port differences between the
A GTX tile consists of a pair of transceivers. For this reason, the GTX transceiver wrapper delivered with the core will always contain two GTX transceiver instantiations, even if only a single GTX is in use. Figure
The 125 MHz differential reference clock is routed directly to the GTX transceiver. The GTX transceiver is configured to output a version of this clock on the REFCLKOUT port: this is then routed to a DCM.
From the DCM, the CLK0 port (125MHz) is placed onto global clock routing and can be used as the 125MHz clock source for all core logic: this clock is also input back into the GTX transceiver on the user interface clock port txusrclk2.
From the DCM, the CLKDV port (62.5MHz) is placed onto global clock routing and is input back into the GTX transceiver on the user interface clock port txusrclk.
It can be seen from Figure
This alternative Receiver Elastic Buffer uses a single block RAM to create a buffer twice as large as the one present in the GTX transceiver. It is able to cope with larger frame sizes before clock tolerances accumulate and result in emptying or filling of the buffer. This is necessary to guarantee SGMII operation at 10 Mbps where each frame size is effectively 100 times larger than the same frame would be at 1 Gbps because each byte is repeated 100 times (see “Designing with
With this fabric Rx Elastic Buffer implementation, data is clocked out of the GTX transceiver synchronously to rxrecclk0 (62.5MHz) on a
Virtex-5 RocketIO GTX Wizard
The two wrapper files immediately around the GTX transceiver pair,
rocketio_wrapper_gtx_tile and rocketio_wrapper_gtx (see Figure
The CORE Generator log file (XCO file) which was created when the RocketIO GTX Wizard project was generated is available in the following location:
<project_directory>/<component_name>/example_design/transceiver/ rocketio_wrapper_gtx.xco
This file can be used as an input to the CORE Generator to regenerate the RocketIO wrapper files. The XCO file itself contains a list of all of the GTX Wizard attributes which were used. For further information, please refer to the
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