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Circuit Training Netlist Representation

Circuit Training uses the Tensorflow MetaGraphDef proto to exchange netlist information. Each node in the graph can represent macros, standard cells, ports, and macro pins. You can find an example of the netlist format for Ariane RISC-V CPU here.

The TILOS-AI-Institute has created a script to convert LEF/DEF and Bookshelf to the Netlist Protocol Buffer format.

Example Netlist

Node types

Note: All the length fields are in microns.

Macro

A macro is a relatively large rectangular block, representing a memory block, with the following fields defined:

  • name
  • attr
    • type: Its placeholder value is set to macro
    • height, width
    • x, y: Coordinates of the center of the macro.
    • orientation, one of N, FN, S, FS, E, FE, W, FW. (Note that 90 degree rotations are not allowed, if, for example, the initial orientation is one of N, FN, S, FS, then it can’t be changed to E, FE, W, or FW.)

Macro Orientation

Soft Macro

A standard cell cluster is treated as a "soft" macro and has the same attribute as normal macros. To distinguish them from memory blocks, soft macros' name starts with Grp.

Standard Cell

A standard cell is a basic building block that implements a combinational or sequential gate. The fields defined:

  • name
  • input : Repeated field that lists all nodes whose inputs are driven by the output of this cell. We are assuming (true for almost all the time) that there’s a single output of the standard cell.
  • attr
    • type: Its placeholder value is set to stdcell
    • height, width
    • x, y: Coordinates.
    • weight: Weight for the net this node is driving. Default value is 1.

Port

A port is a dimensionless element that resides inside or on the edges of the placement area. The fields:

  • name
  • input : Repeated field that lists all nodes that are driven by this port.
  • attr
    • type: Its placeholder value is set to
    • port
    • side: One of top, bottom, left, right.
    • x, y: Coordinates.
    • weight: Weight for the net this node is driving. Default value is 1.

Macro pin

A macro pin is a dimensionless element that is attached to a macro. Its position is given relative to the center of the macro. The fields:

  • name
  • input : Repeated field that lists all nodes driven by this pin.
  • attr
    • type: Its placeholder value is set to macro_pin
    • macro_name: Name of the macro that this pin belongs to.
    • x_offset, y_offset: Position relative to the center of the macro (according to normal placement).
    • x, y: Coordinates (optional).
    • weight: Weight for the net this node is driving. Default value is 1. If multiple std cells in a soft-macros drive std cells in another soft-macro, the weight will be larger than 1.

Net

A net is implicitly defined by the input fields of the macro pins, standard cells, and ports.

In case of soft macros (i.e., cluster standard cells) pins, the weight attribute is used as a multiplier for the wirelength estimation. For example, if N different wires in soft macro Grp_a are driving std cells in soft macro Grp_b, the weight attribute of Grp_a’s pin is set to N.