backend-substitution

The backend-substituion statement is used to customize the symbol generation when exported to a particular backend, like Kicad or Altium.

This backend-substitution statement is primarily useful for net symbols like the ground symbol or the power arrow symbol. Certain backends have a restricted set of net symbols that can be created in these cases. This statement allows the user to customize which symbol will be used on these backends.

Altium ground and supply symbols are in the ocdb/utils/symbols package of the open-components-database repository.

Signature

  backend-substitution(<String>) = <SchematicSymbol>
  ...

• <String> - A string literal for the backend this statement targets.
  • "Altium" targets "Altium Designer" export
  • "Kicad" targets "Kicad" export.
• <SchematicSymbol> - A schematic symbol definition created using the pcb-symbol statement.

Usage

For certain symbols, we might want to customize the symbol construction depending on the backend (ie, the export target).

public pcb-symbol ground-sym :
  pin p[0] at unit-point(0.0, 0.0)
  
  unit-line([[0.0, 0.0], [0.0, -0.5]])
  unit-line(0.1, [[-0.5, -0.5], [0.5, -0.5]])
  unit-line(0.1, [[-0.3, -0.7], [0.3, -0.7]])
  unit-line(0.1, [[-0.1, -0.9], [0.1, -0.9]])

  unit-val([-1.0, -1.5])
  preferred-orientation = PreferRotation([0])
  backend-substitution("Altium") = altium-power-gnd-power-sym

Here the default symbol geometry gets created on all platforms except Altium, which gets a customized Power Port Symbol, specifically, the "Power Ground" symbol.

The backend gets selected with the set-export-backend function.