We are looking to design a custom carrier board to support the ZU11EG SOM and FMCOMMS8 daughterboard and I wanted to raise a few questions about the proper configuration of the HMC7044(s)
- It seems that the HMC7044 on the carrier board is required to provide common, length matched CLKIN/RFSYNCIN inputs into the HMC7044s on the SOM and the FMCOMMS8. Is this correct or is there some way to achieve synchronization between the SOM and the daughterboard without a separate HMC7044 on the carrier?
- Our clock source will be a GPS module with both a 10 MHz and 1 PPS output. On 2019R2, we have attempted to configure the SOM HMC7044 for a 10 MHz input on CLKIN2. However, when we attempt to configure this via the device tree, it seems the hmc7044 driver comes up with some improper values for the PLL dividers, including setting the OSCIN prescaler value at 0x0020 to 0. We were only able to achieve lock to 10 MHz by manually writing several registers. Does the driver not support a 10 MHz input and will we need update this for our application?
- On 2019R2, it appears that the SOM and daughterboard HMC7044s are both configured to favor CLKIN1 for PLL1 and then uses CLKIN0/RFSYNC as RFSYNC. It seems like both of these are fed from the carrier HMC7044 outputs at 30.72 MHz (/96 on those outputs). Separately, it also seems that the SYNC inputs are also fed by 3.84 MHz (/768 on those outputs) outputs from the carrier HMC7044. Is this correct? Are both SYNC and RFSYNC required are are those the correct input frequencies?
- Based on the above, it would seem that what we would need to do to clock off of the GPS module would be to configure the carrier HMC7044 to accept 10 MHz on CLKIN1 and then the SOM and the daughterboard will be fed from the carrier outputs? Should we also use the 1PPS_SYNC output as a RF SYNC on CLKIN0/RFSYNC or can we connect 1 PPS to the SYNC input on the carrier HMC7044?