Fabit is invoked from the UNIX prompt by simply typing fabit. Once you have run Fabit, it will ask you a series of questions. In order to create a correct .fab file, it is necessary to have the following available:
Fabit requires a Carafe technology file to operate. It uses the tech, types, contact, and route sections of the specified technology file to determine the process layers to list in the .fab file. It uses the bridge section to determine which pairs of layers may be bridged together and the extract section to determine transistor layers.
The name of the fabrication process can be used as a description so that the user knows which .fab file is being used when running Carafe. It is suggested that .fab files with different specifications should have different names.
Fabit can do two different kinds of defect size checking. It can ignore defects that are to small to cause a fault, and/or defects that could potentially cause compound faults. A defect is considered to small to cause a bridge if where r is the defect radius and s is the minimum spacing for layer i. A defect is considered to small to cause a break if where r is the defect radius and w is the minimum width of layer i. A defect is considered capable of causing compound bridge faults if where r is the defect radius, w is the minimum width for layer i, and s is the minimum spacing for layer i. A defect is considered capable of causing a compound break fault is where each variable is the same as before. If either minimum or maximum defect size checking are needed, then Fabit must be told the minimum width and spacing rules for each layer. If neither are needed, then Fabit will not prompt for the rules.
Next, Fabit will prompt for the GOS scaling factors. Fabit uses the layers specified in the extract section of the technology file to determine transistor types. The scaling factors must be between 0 and 1 (inclusive).
Next, Fabit will prompt for the relative probabilities and defect distributions for each pair of bridgeable layers listed in the bridge section of the technology file. If fifty percent of the bridges that occur are bridges from metal1 to metal1, then enter .5 when asked Enter probability (metal1 to metal1). Fabit will then prompt for a defect distribution for that bridge type. Once all relative probabilities have been entered, Fabit will normalize the probabilities to 1.0. If there is more than one radius, Fabit will distribute the normalized value across all the radii using the equation: .
Next, Fabit will prompt for the relative probabilities and defect distributions for break faults. Each routeable layer and contact type is considered breakable by Fabit, and each has its own probability and defect distribution. Once all probabilities have been entered, Fabit will normalize the probabilities to 1.0. Again, if there is more than one radius, Fabit will distribute the normalized value across all the radii using the equation: .
If an improper value is entered at one of the prompts, Fabit will generate an error message. This usually means that the last value entered was not an acceptable value, fabit will tell you why the value was not acceptable and prompt for the information again. Once all the questions have been answered, Fabit will respond with ``Fab file written to disk."
Data files created by Fabit can be piped back into Fabit to create a new .fab file. Data files may contain comment lines beginning with a ``#'' character to make modifying them easier. Note that the normalized probabilities will appear in the data file, and may differ from those entered.