CLHS M/X Protocol IP cores
Five message types are available in CLHS: a low-latency (<1µs) 0ns jitter trigger for real-time imaging at up to 8MHz with seven separate modes, 16 bidirectional general-purpose I/Os with <1µs latency, remote DMA video packet and frame grabber data forwarding, high-speed command uplink enabling streaming correction coefficients, and revision information used in device discovery. One of the big values of CLHS is that it is a real-time, point-to-point interface. In the context of the CLHS triggers and GPIO, the low latency means immediate responses, eliminating the need for tracking and scheduling as might be the case with other interfaces. The CLHS X Protocol can connect to a 10Gbase-KR Ethernet PHY physical (Figure 2) for FPGAs that don’t have built in 10Gbps transceivers or use the provided Physical Coding Sublayer (PCS) module to implement the code within 10Gbps-capable FPGAs that don’t offer the 10Gbase-KR capability (Figure 3). Because of the unique way the CLHS X Protocol is implemented, Camera Link HS is already in the final stages of moving the specification to 25Gbps.
Ready for 25Gbps
The well-designed IP core architecture makes CLHS ready without any modification to move to 25Gbps on an FPGA using 25Gbps transceivers over fiber with SFP28 or QSFP28 or MPO connectors. The soon-to-be-released specification revision will validate CLHS as having up to 100Gbps (4×25Gbps) available bandwidth using a single MPO connector. In achieving this speed increase, the CLHS X Protocol IP core remains completely unchanged. Therefore, all existing CLHS infrastructure also remains unchanged, making the move to 25Gbps inexpensive and straightforward for vendors and users. Contrast this with frame grabber interfaces that need to change core code and move to different line encoding to implement faster rates. Furthermore, CLHS has a very flexible and robust mechanism for changing the speed of the interface. Using MPO to LC, breakout cables, or SFP28 allows backward compatibility to existing CLHS 10Gbps frame grabbers or newly developed 25Gbps frame grabbers to support existing 10G cameras.