Games / Command flash cards / Layout and parasitic formats / GDSII (Graphic Design System II) and mask data

GDSII (Graphic Design System II) and mask data

Each card shows a command to explain. A missed card returns later in the round and starts the schedule over. A card answered correctly moves up the schedule and next appears after 1, 3, 7, then 21 days. Keys 1 to 4 choose an option, h shows a hint, and Enter moves on. A hint keeps the card where it is on the schedule. An ordering card is answered by clicking its items in order, and one wrong click ends it. Time values are in nanoseconds. Progress is stored in this browser.

SourceFour formats carry a design between tools: LEF (Library Exchange Format) for the technology and the cells, DEF (Design Exchange Format) for the layout, SPEF (Standard Parasitic Exchange Format) for extracted wires, and SDF (Standard Delay Format) for annotated delays. The LEF (Library Exchange Format) excerpts here are quoted from the Nangate45 files that OpenROAD-flow-scripts ships; the rest follow the formats as OpenROAD and OpenSTA read them. Reference: the OpenSTA command reference (the open flow on GitHub).
All 5 cards in this section, with answers
  • library GCD structure INV_X1 boundary layer 11 datatype 0 ( ... ) path layer 10 datatype 0 ( ... ) structure gcd sref INV_X1 at (12540, 28000) reflection
    A hierarchy of cells built from polygons and references.

    Hint: One structure refers to another rather than repeating it.

    A boundary is a filled polygon and a path is a wire with a width. A structure reference places another structure at a point, with an optional flip or rotation, and an array reference repeats one on a grid. This is why a full chip stays a manageable file even with billions of shapes. the open flow reference

  • metal1 drawing -> layer 11 datatype 0 metal1 pin -> layer 11 datatype 2 metal1 label -> layer 11 datatype 251
    Named layers translated into the numbered pairs the file stores.

    Hint: The name on the left is what the tools use. Ask what the foundry uses.

    GDSII (Graphic Design System II) knows only numbers, so a layer map translates each named purpose into a layer and datatype pair. Getting one wrong sends the foundry a file where pins are drawn as metal or labels are missing, and the rule deck reads the same numbers, so the mistake often passes unnoticed until the checks disagree. the open flow reference

  • INV_X1 in LEF (Library Exchange Format) INV_X1 in GDSII (Graphic Design System II)
    The abstract with pins and blockages, against every polygon in the cell.

    Hint: One of the two is what the placer and router read all day.

    The abstract carries only what the tools above need: size, pin shapes, and where routing may not go. The layout carries the transistors. They are merged at the end, when the placed abstracts are replaced by the real cells, which is why the two must agree about pin positions exactly. the open flow reference

  • OASIS (Open Artwork System Interchange Standard)
    A newer layout format that stores the same shapes far more compactly.

    Hint: Both hold the same layout. Ask what changed between the two formats.

    The older format's fixed-width records become bulky at modern densities, where fill alone runs to hundreds of gigabytes. The newer one encodes repetition directly and can shrink a file by a factor of ten. Both are accepted, and the choice is the foundry's. the open flow reference

  • xor old.gds new.gds -> differences by layer
    A shape-by-shape comparison showing only what changed.

    Hint: Ask what an empty result would mean.

    After a late change, this is how a team proves that only the intended layers moved. A metal-only fix must show differences on the metal and via layers and nothing on the transistor layers, and a fill-only run must show nothing but fill. the open flow reference