The SLR Crossing by Hierarchy table shows you the hierarchy of the driving cells for nets that cross an SLR, along with the driving primitive type. You can use it to identify hierarchies that source a large number of crossings, helping you formulate actions that have the maximum impact.
The following is an example of the
report:
6. SLR Crossings by Hierarchy of Driver
---------------------------------------
+-------------+--------+-------+------------+--------+-----------------+
| # Crossings | DCMAC | FDCE | GTME5_QUAD | SRL16E | Hierarchy |
+-------------+--------+-------+------------+--------+-----------------+
| 20 (0) | 8 (0) | 5 (0) | 5 (0) | 2 (0) | TOP |
| 18 (1) | 8 (1) | 5 (0) | 5 (0) | 0 (0) | lev1A |
| 17 (17) | 7 (7) | 5 (5) | 5 (5) | 0 (0) | lev1A/Lev2A |
| 2 (2) | 0 (0) | 0 (0) | 0 (0) | 2 (2) | lev1B |
+-------------+--------+-------+------------+--------+-----------------+In this design, there are 20 crossing nets: 18 from lev1A and two from lev1B. Of the crossing nets within lev1A, 17 are sourced from the lower-level hierarchy lev1A/lev2A (as indicted by the number in parenthesis), and one is sourced from within lev1A.
You can use the table to identify primitives that are undesirable drivers for
SLR crossings. In high-performance designs, drivers of SLR crossings are typically
registers (such as FDRE or FDCE) because they can be easily replicated and provide
the fastest timing profile. Other primitive types can lack placement flexibility or
replication capability, which limits the tool’s ability to resolve timing problems
on SLR crossing paths.
Note: Follow the
instructions in the footnote to further examine the nets driven by a given
primitive in the schematic or netlist windows.