Versal devices have a clocking structure similar to AMD UltraScale™ devices, where global clocking is used throughout the device but the loads can be placed regionally or globally. Multi-clock buffer (MBUFG) primitives in Versal devices allow for clock division at the leaf level. This clock division reduces clock track utilization. It also improves timing on synchronous clock domain crossings. This architecture results in an efficient clock resource utilization, support for an increased number of design clocks, and improved clock characteristics for performance and power.
In Versal devices, the columnar HDIO banks or the horizontal high performance XPIO banks typically source clocks. Each Versal device clock region contains a clock network routing. This routing is divided into 24 vertical routing tracks. It also includes 12 horizontal routing tracks, 24 vertical distribution tracks, and 24 horizontal distribution tracks. The bottom clock region row is unique and contains 24 horizontal routing tracks (versus the 12 horizontal routing tracks in the other clock region rows).
Following are the main categories of clock types and associated clock structures grouped by their driver and use:
- High Speed I/O Clocks
These clocks are associated with the SelectIO™ XPHY Logic and are generated by the XPLL. The XPLL routes these clocks via dedicated, low-jitter resources to the XPHY logic. This setup supports high-performance I/O interfaces. In general, this clocking structure is controlled by AMD IP. Examples include the NoC IP DDR4 memory controller, soft memory controller IP, or the Advanced IO Wizard IP.
- General Clocks
Most clock tree structures use these clocks. They can be sourced by a GCIO package pin or clock modifying blocks, such as an MMCM, XPLL, or DPLL. The typical BUFGCE/BUFGCE_DIV/BUFGCTRL buffers must drive the general clocking network. Alternatively, the new MBUFGCE/MBUFGCE_DIV/MBUFGCTRL primitives can drive it. These new primitives allow for leaf-level clock division.
HDIO banks provide limited clocking resources by offering only the DPLL and the BUFGCE. A given clock region can support up to 24 unique clocks. Versal devices can support over 100 clock trees. This depends on topology, fanout, and load placement.
- Gigabit Transceiver Clocks
The transmit, receive, and reference clocks of gigabit transceivers (GT*_QUAD) use dedicated clocking in the clock regions that include the GTs. In Versal devices, the GT clocking columns contain DPLLs and also support the new MBUFG_GT primitive for leaf-level clock division. You can use GT clocks to achieve the following results:
- Drive the DPLLs for frequency synthesis, jitter filtering, or clock deskew.
- Drive the general clocking network using the BUFG_GT or MBUFG_GT buffers to connect any loads in the fabric.
- Share clocks across several transceivers in the same or different Quad.
Note: Only the 12 even clock routing and clock distribution tracks cross the SLR boundary in the GT column.Note: No clock routing and clock distribution tracks cross the SLR boundary in the GT column to and from the top SLR of the AMD Versal™ HBM devices. Placer ignores a USER_CLOCK_ROOT in the GT column when loads span the top SLR and other SLRs.