return_path.hpp File Reference

Reference-return audit of high-speed nets (issue #7, docs/05-routing.md §42, D114). More...

#include <string>
#include <utility>
#include <vector>
#include <nlohmann/json.hpp>
#include "geom/point.hpp"
#include "model/board.hpp"
#include "model/rules.hpp"

Go to the source code of this file.

Classes
struct	tmk::analysis::ReturnPathOptions
struct	tmk::analysis::ReturnVoid
struct	tmk::analysis::ReturnLayerChange
struct	tmk::analysis::ReturnEnd
struct	tmk::analysis::NetReturn
struct	tmk::analysis::ReturnPathReport

Namespaces
namespace	tmk
namespace	tmk::analysis

Functions
ReturnPathReport	tmk::analysis::analyse_return_paths (const model::Board &b, const model::DesignRules &rules, const ReturnPathOptions &opt)
	Analyses the nets the options select on b as it stands (routed copper included). Deterministic.
nlohmann::json	tmk::analysis::return_path_json (const model::Board &b, const ReturnPathReport &r)
	The report as JSON (nanometres converted to millimetres), and one return_path viewer message per net (docs/13-viewer-protocol.md).
std::string	tmk::analysis::return_path_message (const model::Board &b, const NetReturn &n)
std::vector< std::string >	tmk::analysis::return_path_lines (const model::Board &b, const ReturnPathReport &r)
	A one-line text form per net and the lines under it that explain a warning.

Detailed Description

Reference-return audit of high-speed nets (issue #7, docs/05-routing.md §42, D114).

KiCad's DRC cannot tell whether a fast trace has continuous copper under it. A dogbone escape punches antipads through the reference pour, a plane can be split, a layer change can come without a nearby stitch: the signal is DRC-clean and its return current still walks around the void, which grows the loop area and the inductance. This pass answers a geometric question per net: does the trace have copper under it on the adjacent reference layer, and where it does not, how far does the return detour?

It is read-only (it adds nothing to the board) and it is a geometric model, not a field solver: the return of a signal over copper is taken to be its mirror image on the reference layer, across a void it is the shortest path that stays on the remaining reference copper (Dijkstra over the visibility graph of the reference polygon's vertices; Lee and Preparata 1984), and at a layer change it closes through the nearest stitching via of the reference net, or the nearest capacitor between the two reference nets, within a radius. The return does not close through "one assumed GND ball": at a footprint the nearest pad of the reference net is the assumed return pad (the comment on the issue).

Definition in file return_path.hpp.