4.3.3. SYNC_N Signal
In some applications, multiple converters are grouped together in the same group path to sample a signal (referred as multipoint link). The FPGA can only start the LMFC counter and its transition to ILAS after all the links deassert the synchronization request. The JESD204B TX IP core provides three signals to facilitate this application. The SYNC_N is the direct signal from the DAC converters. The error signaling from SYNC_N is filtered and sent out as dev_sync_n signal. For Subclass 0, you need to multiplex all the dev_sync_n signals in the same multipoint link and then input them to the IP core through mdev_sync_n signal.
For Subclass 1 implementation, you may choose to combine or not to combine the SYNC_N signal from the converter device. If you implement two ADC converter devices as a multipoint link and one of the converter is unable to link up, the functional link still operates. You must manage the trace length for the SYSREF signal and also the differential pair to minimize skew.
The SYNC_N is the direct signal from the DAC converters. The error signaling from SYNC_N is filtered and sent out as dev_sync_n output signal. The dev_sync_n signal from the JESD204B TX IP core must loopback into the mdev_sync_n signal of the same instance without combining the SYNC_N signal.
You must set the same RBD offset value (csr_rbd_offset) to all the JESD204B RX IP cores within the same multipoint link for the RBD release (the latest lane arrival for each of the links). The JESD204B RX IP core deskews and outputs the data when the RBD offset value is met. The total latency is consistent in the system and is also the same across multiple resets. Setting a different RBD offset to each link or setting an early release does not guarantee deterministic latency and data alignment.