The main purpose of the Clocking FMC is to test/prototype the clocking circuit proposed in the WRS-4 main board (Hardware_Architecture), section 3.4 (page 25-28). Additionally, the FMC has an SFP cage and it can be used to enable WR on a host board, such as e.g. AFCZ, or ZCU102/ZCU106 eval board.
The figure shows a detailed block diagram of the proposed solution. As can be seen in
this figure, the main PLL is the HMC7044 that has the following features of interest for the
Possibility to have a mixed scenario (part of the design working with 62.5 MHz
recovered clock and another part with 156.25 MHz recovered clock, for 1Gbps and
10Gbps links respectively).
Deterministic phase alignment between all output channels, allowing to generate the
10 MHz output directly from the HMC7044 PLL with SYNC support.
Plenty of clock outputs with configurable type (LVDS or LVPECL).
The main oscillator is the DOT050V that has a plastic cover to avoid known problems
related to the airflow. For the helper clock, we propose to use the programmable and tunable oscillator
Si549 that has already been tested in a WR node and is ideal to support different
frequencies. The 1PPS and Abscal outputs will be latched with D-type FF (with 125MHz or
250MHz). The design will have the possibility to mount an oscillator board (a type of module
expansion) to allow better oscillator OCXO and DDS for lpGBT.
The Grandmaster 10 MHz input clock is multiplied by deterministic LMX2594 PLL to
create a 1-PPS aligned 62.5/125 MHz, thus the SoftPLL of the WR PTP implementation can
align to it. As such, it is the safest solution in case of loss of the 10 MHz input reference.
Another option for the Grandmaster can be to connect the RFU of the HMC7044 directly with
the LMX2594 in order to clock the system directly with 10 MHz input clock (multiplied to 2.5
GHz) and without using the main oscillator DOT050V. The main problem of this last option
occurs when the input reference is lost, since the system might freeze. The RFU lines of
HMC7044 can also be connected to the expansion board.