Value change dump

An extended VCD format defined six years later in the IEEE standard 1364-2001 supports the logging of signal strength and directionality.

The simple and yet compact structure of the VCD format has allowed its use to become ubiquitous and to spread into non-Verilog tools such as the VHDL simulator GHDL and various kernel tracers.

The header section of the VCD file includes a timestamp, a simulator version number, and a timescale, which maps the time increments listed in the value change section to simulation time units.

Several variables can share an identifier if the simulator determines that they will always have the same value, i.e. are the same wire in the scope of the overall netlist.

The section beginning with $dumpvars keyword contains initial values of all variables dumped.