Application Notes; Xapp648: Serial Backplane Interface To A Shared Memory; Xapp649: Sonet Rate Conversion In Virtex-Ii Pro Devices; Xapp651: Sonet And Otn Scramblers/Descramblers - Xilinx RocketIO User Manual

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Application Notes

XAPP648: Serial Backplane Interface to a Shared Memory

This application note utilizes the Virtex-II Pro™ RocketIO™ transceivers and the Xilinx Aurora
Protocol Engine to provide a multi-ported interface to a shared memory system in a backplane
environment. Multiprocessor systems are often encountered in backplane systems, and distributed
processing applications require access to a shared memory across a backplane bus. Utilization of a
hardware test-and-set lock mechanism, along with a software protocol to test for a semaphore grant
prior to accessing the shared memory, guarantees atomic access to the shared memory.

XAPP649: SONET Rate Conversion in Virtex-II Pro Devices

The RocketIO transceivers have several modes of operation, but all modes rely on the internal
transmitter clock being multiplied by 20 for data transmission. For example, a 20-bit data stream
passed to the unit at 125 MHz is serialized and retransmitted at 2.5 Gb/s. At a 156.25 MHz input, the
output is at its maximum speed of 3.125 Gb/s. The parallel data stream applied to the RocketIO
transceiver can either be 20 bits direct, or it can be written as 16 bits, to which 8b/10b coding is
applied to generate the 20 bits required.
However, there is a class of applications, typically in SONET processing systems, where the data
path is 16 bits wide, running at 155.52 MHz. The designer would ideally apply the data directly to
the RocketIO transceiver for onward transmission at 155.52 x 16 = 2.48832 Gb/s. Since this cannot
be done in Virtex-II Pro devices, this application note describes the logic necessary to perform this
function.
This application note is divided into two sections, the first is the logic necessary for the data width
conversion, and the second describes the clocking characteristics required by the RocketIO
transceiver.

XAPP651: SONET and OTN Scramblers/Descramblers

Both SONET and OTN are standards for data transmission over fibre optic links. This implies a
need for clock recovery at the receiver, which in turn requires a guaranteed minimum number of
transitions in the incoming serial data stream. The mechanism to achieve this transition density,
similar for both SONET and OTN, is known as scrambling. The scrambling (and descrambling)
function is independent of the serial data rate used. Serial data for transmission is added to the output
RocketIO™ Transceiver User Guide
UG024 (v2.3.2) June 24, 2004
www.xilinx.com
1-800-255-7778
Appendix C
143