TMC-20603: Registers with High Immediate Fan-Out Span
- There are two types of sink: Immediate Fan-Out and Timing Path Endpoint.
- There are two types of pull: Tension and Span.
Immediate Fan-Outs are the immediately connected nodes (lookup tables, other registers, RAM or DSP blocks, and others) of the register. This is equivalent to fan-outs that the Chip Planner displays, and in various high fanout reports. Register Duplication directly distributes the immediate fan-outs of a register among the duplicates.
Span is the maximum one dimensional delta between the left/bottom-most sink, and the right/top-most sink. The Span value is therefore independent of the number of sinks, and it is good at detecting registers that drive a long distance in opposite directions. Register duplication can allow duplicates to travel in each direction to more efficiently disperse the signal.
Recommendation
Registers with high span among immediate fan-outs prevent the Compiler from properly localizing connections, and can warp the optimization of placement and routing.
Severity
Low
Stage
Place, Finalize
Device Family
- Intel® Stratix® 10
- Intel® Agilex™