Standard Parasitic Exchange Format - The Difference Between Parasitic Data Formats

The Difference Between Parasitic Data Formats

SPEF is not the same as SPF (including DSPF and RSPF). Detailed Standard Parasitic Format is a very different format, meant to be useful in a SPICE simulation. For example, NET sections do not have endings, and comments should start with two asterisks. A brief syntax of the DSPF format is as shown:

*DSPF 1.0 *DIVIDER / *DELIMITER : *BUS_DELIMITER *|GROUND_NET NetName .SUBCKT *NET NetName NetCap *|I(InstancePinName InstanceName PinName PinType PinCap X Y) *|P(PinName PinType PinCap X Y) *|S(SubNodeName X Y) .ENDs .END

The acronyms stand for:

SPF—Standard Parasitic Format

DSPF—Detailed Standard Parasitic Format

RSPF—Reduced Standard Parasitic Format

SPEF—Standard Parasitic Exchange Format

SBPF—Synopsys Binary Parasitic Format

SPF is a Cadence Design Systems standard for defining netlist parasitics. DSPF and RSPF are the two forms of SPF; the term SPF itself is sometimes used (or misused) to represent parasitics in general. DSPF and RSPF both represent parasitic information as an RC network. RSPF represents each net as an RC "pi" model, which consists of an equivalent ”near" capacitance at the driver of the net, an equivalent "far" capacitance for the net, and an equivalent resistance connecting these two capacitances. Each net has a single "pi" network for the network, regardless of how many pins are on the net. In addition to the pi network, RSPF causes the PrimeTime tool to calculate an Elmore delay for every pin-to-pin interconnects delay.

In contrast, DSPF models a detailed network of RC parasitics for every net. DSPF is therefore more accurate than RSPF, but DPSF files can be an order of magnitude larger than RSPF files for the same design. In addition, there is no specification for coupling caps in DSPF. DSPF is more similar to a SPICE netlist than the other formats. SPEF is an Open Verilog Initiatve (OVI)--and now IEEE—format for defining netlist parasitics. SPEF is NOT identical to the SPF format, although it is used in a similar manner. Like the SPF format, SPEF includes resistance and capacitance parasitics. Also like the SPF format, SPEF can represent parasitic in detailed or reduced (pi-model) forms, with the reduced form probably being more commonly used. SPEF also has a syntax that allows the modeling of capacitance between different nets, so it is used by the PrimeTime SI (crosstalk) analysis tool. SPEF is smaller than SPF and DSPF because the names are mapped to integers to reduce file size.

SBPF is a Synopsys binary format supported by PrimeTime. Parasitic data converted to this format occupies less disk space and can be read much faster than the same data stored in SPEF format. You can convert parasitics to SBPF, by reading them in and then writing them out with the write_parasitics -format sbpf command.