IEEE 1800-2012 also supports real nettype port connections. During elaboration, the net is collapsed to a single location in the system and referenced by all attached modules. Nettype port connections are more efficient and support inout ports, where each module directly connects to the net. It also supports multiple drivers. It also supports `wrealZState and `wrealXState values to define high impedance and invalid drive conditions, respectively.
A user-defined nettype is declared with the keyword nettype, and includes a data type and optionally a resolution function. It can carry one or more values over a single net. A real value can be used to communicate voltage, current and other values between design blocks. You can define a user-defined type (UDT), user-defined nettype (UDN), and user-defined resolution function (UDR).
Syntax:
nettype UDT UDN [ with UDR ];
Where,
UDTis the datatypeUDNis the nettype identifiedUDRis the resolution function
UDNs are SystemVerilog structures with a defined resolution function. Nets are used for structural connections and allow for the resolution of multiple drivers. Nets have a single, resolved value based on one or more drivers. Nettypes can only be driven through a continuous assignment, where each assignment represents a driver on the net. A nettype construct can carry one or more values over a single net. A real value can be used to communicate voltage, current, and other quantities between design blocks.
Resolution functions are used to determine the final value of a nettype. The return value of a resolution function is the nettype’s datatype. It is called whenever there is a change on one or more drivers to a net. Nettypes that are defined to only have a single driver do not need to be defined with a resolution function. However, a nettype with a resolution function that has only one driver can still call that resolution function when a driver changes. Also, you can use a resolution function with a single-driver nettype. The resolution function can be used to define monitoring functionality and debug operations on the net.