grt/drt: Add support for routing secondary power nets#10661
Conversation
Implement routing support for secondary power nets (non-special supply nets in the NETS section with pre-routed straps/SWires). - In GRT, identify secondary power nets and route their pins directly to the closest coordinates on their pre-routed straps. - In DRT, bypass the DRT-0305 error check for these nets, import pre-routed straps as fixed wires, and treat their type internally as SIGNAL so TritonRoute routes cell pins directly to the straps. - Add regression test case registered in both CMake and Bazel. Fixes The-OpenROAD-Project#8770 Fixes The-OpenROAD-Project#8771 Signed-off-by: KMohnishM <kmohnishm@gmail.com>
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Code Review
This pull request introduces support for routing secondary power nets (non-special supply nets) to their nearest straps. It adds helper functions to identify these nets, skips them during standard routing, and implements a dedicated routing routine that connects pins to the closest strap using planar routing and via stacks. The review feedback suggests removing a redundant loop that adds degenerate segments to avoid duplicate guides, and replacing a hardcoded magic number for the layer penalty with a named constant.
| for (int l = min_l; l <= max_l; ++l) { | ||
| route.emplace_back(closest_grid_pt.x(), | ||
| closest_grid_pt.y(), | ||
| l, | ||
| closest_grid_pt.x(), | ||
| closest_grid_pt.y(), | ||
| l); | ||
| } |
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The loop that adds degenerate segments (from (x, y, l) to (x, y, l)) is redundant. The subsequent loop already adds vertical segments (vias) connecting each layer from min_l to max_l, which naturally generates guides on all intermediate layers. Adding these degenerate segments results in duplicate guides being written to the guide file (as seen in secondary_power.guideok where metal1 and metal2 guides are duplicated multiple times). Removing this loop cleans up the route representation and prevents redundant guide generation.
| int64_t dist = std::abs(pin_pt.x() - closest_x) | ||
| + std::abs(pin_pt.y() - closest_y); | ||
| // Prefer straps closer in routing layers | ||
| dist += 1000LL * std::abs(pin_level - swire_level); |
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Define the layer penalty multiplier as a named constant instead of using a hardcoded magic number, in accordance with the general rules of the repository.
constexpr int64_t kLayerPenalty = 1000;
dist += kLayerPenalty * std::abs(pin_level - swire_level);References
- Define tunable parameters as named constants instead of using hardcoded magic numbers.
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grt/drt: Add support for routing secondary power nets
Implement routing support for secondary power nets (non-special supply nets in the
NETSsection with pre-routed straps/SWires).Summary
This PR adds support in both the Global Router (GRT) and Detailed Router (DRT / TritonRoute) to route secondary power nets from cell pins to their nearby pre-routed straps. This resolves both level-shifter secondary power grid routing (#8770) and designs using standard cell libraries without tie cells (#8771).
Proposed Changes:
grt):isSecondaryPowerNetto identify nets that are supply nets, not special, and have pre-routed SWires.GlobalRouter::routeSecondaryPowerNetswhich maps each pin to the absolute closest grid coordinate on its pre-routed strap (clamping boundary coordinates and applying a layer difference penalty). It generates direct planar segments and vertical via stacks to connect them, avoiding daisy-chaining (using star topology).drt):DRT-0305error check for these nets.SIGNALso TritonRoute routes, rips up, and optimizes the pin connections natively. This also naturally ensures any user-configured Non-Default Rules (NDRs) for wire widths and spacing are respected and applied.Type of Change
Impact
Enables the router to automatically route secondary power nets and constant tie-offs to nearby power rails/straps natively, acting as a general fallback for automated flows (e.g. OpenLane) without requiring custom floorplanning/PG scripts.
Verification
./etc/Build.sh).Related Issues
Fixes #8770
Fixes #8771