FOS standard cell generator from scratch

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3D visualization of a 'latch' standard cell. (Made with gds3xtrude)

Abstract

Flow diagram of standard cell generation flow.

Standard-cell based design flows are very common for digital electronics. Usually, standard-cell libraries come with costs and restrictive non-disclosure agreements which are an obstacle for makers, hobbyists and start-ups. NDAs also prohibit collaboration with other groups and make a community driven development very difficult. Having free & open standard-cell libraries would be a partial solution to this problem, but there are many technologies around which require a tailored standard cell library each. Therefore, it would be helpful if standard-cell libraries could be generated from a more abstract description such as a set of netlists and design rules. This talk introduces LibreCell, a free & open-source standard cell generator which has been developed from scratch in the past few month.

Software

General information

Roadmap

  • ✓ Place & route of single row cells
  • ✓ Generate GDS
  • [in progress] Generate LEF
  • ✓ Timing characterization of combinatorial cells
  • [in progress] Timing characterization of sequential cells
  • Timing characterization of cells with tri-state output
  • Timing characterization of cells with asynchronous inputs
  • ✓ Generate synthesis liberty file (currently only for combinatorial cells)
  • Capacitance extraction using a field solver (maybe FasterCap)

Open challenges

  • Netlist synthesis (e.g generate an 'optimal' transistor netlist from a boolean expression)
  • Automated transistor sizing
  • Routing: Implement router for finer routing pitch to allow more compact cells.
  • LEF output: might not be compatible with tools yet. (Pin direction is not yet inferred from the netlist. OBS field ('obstructions') is yet missing).
  • Automated LVS check (using KLayout DVB)
  • Automated DRC check (using KLayout)
  • Capacitance extraction with FasterCap
  • Characterization: complete liberty files such that they can be used by synthesizers

References