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ATCA-3671 Clocking Features

NI ATCA FPGA Modules Help

Edition Date: March 2017

Part Number: 376468A-01

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The ATCA-3671 provides a number of options for configuring onboard and external clocks to meet the needs of a wide range of applications.

The clocking resources available on the system are summarized in the table below. If the software programming environment provides support for runtime configuration of clocking resources, refer to specific software product documentation, such as LabVIEW Help, for more information.

The following table describes the ATCA-3671 Clock Sources.

Name Direction Description
Fixed 100 MHz N/A A single 100 Fixed MHz reference clock is distributed to all four FPGAs on the ATCA-3671. This clock is free-running and may be used to derive any other clock frequencies desired inside the FPGA.
DDR3 Clock N/A A single 400 Hz reference clock is distributed to all four FPGAs on the ATCA-3671 for explicit use by the soft double data rate type three (DDR3) memory controller logic in the FPGA. The actual frequency of the logic clock available on the user interface side of the memory controller may vary based on the software platform, but is typically 167 MHz for the maximum DDR3 dynamic random access memory (DRAM) speed of 1,333 MHz.

SYNC A

SYNC B

Input

Each of these two independent signals can be used to drive a clock to all four FPGAs on the ATCA-3671. By default, the SMA input on the front panel of the system is enabled as the signal source. However, in environments where a full ATCA backplane is present, this setting can be overridden in firmware to select the corresponding ATCA backplane signals to use the source instead.

When added to a LabVIEW project, these clock sources are defined as free-running base clocks which support derived clocks. Therefore, the external clock source must be connected and stable at the correct frequency before running the FPGA application, even if they are not explicitly used in the diagram. Otherwise, errors will be reported. In addition, the SYNC A and SYNC B signals must not be used as clocks in the same application (and vice versa) if they are used as FPGA I/O.

CLK IN/OUT A

CLK IN/OUT B

CLK IN/OUT C

CLK IN/OUT D

Input/Output

Each of these connectors on the front panel are coupled to one FPGA on the ATCA-3671 (denoted by A, B, C, or D) as either an input or output. The direction of the signal is configured in software, and can be changed dynamically at runtime.

In LabVIEW, this clock source for each FPGA is defined as an external clock. This implies that it may not always be stable or connected and therefore cannot be used as the default top level clock or to generate derived clocks.

JC OUT A

JC OUT B

JC OUT C

JC OUT D

Output Each FPGA on the ATCA-3671 can drive out an ultra-low phase noise clock through a designated on-board jitter cleaning phase-locked loop (PLL). The exact frequency configuration of this PLL is controlled by software.

MGT REF

Input An input on the front panel used to distribute a single multi-gigabit transceiver (MGT) reference clock to every user-accessible high-speed transceiver on all four FPGAs on the ATCA-3671.

AIO CLK

Input An input on the front panel used to drive an auxiliary external clock into all four of the AIO slots on the front panel of the ATCA-3671. This clock is not driven directly into the FPGA. Therefore, its usage and availability are dependent on the ATCA I/O module present in the system.

 

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