vcd2svg

vcd2svg is a public domain vcd to svg converter written in AWK.

Usage

After compiling and running the simulation, call vcd2svg with the vcd file as its input and redirecting its output to a svg file. The variables that should be displayed in the svg needs to be listed as arguments to vcd2svg. For example, to show the variables clk, data and out on the waveform from the file sim.vcd to the file sim.svg, run the following command.

$ vcd2svg clk data out <sim.vcd >sim.svg

Each variable can be followed by a colon and a letter indicating the notation for the labels. This letter can be h for hexadecimal, u for unsigned decimal, d for signed decimal, or b (the default) for binary.

$ vcd2svg clk:b data:u out:h <sim.vcd >sim.svg

When run without arguments, vcd2svg list all the variables in the input.

$ vcd2svg <sim.vcd
outer.clk
outer.data
outer.out
outer.inner.signal
outer.inner.acc
outer.inner.out

Observe that the variables are listed prefixed with the period-delimited path of modules that contains it. For example, the variable clk is used in the module outer; while the variable acc is used in the module inner, which is instantiated by the module outer. The full path of a variable can be used in the command-line arguments, for disambiguation.

$ vcd2svg clk outer.inner.signal outer.inner.out <sim.vcd >sim.svg

Variables can be set with the -v option, as in -v VARIABLE=VALUE. The following variables are supported by vcd2svg:

• from: Beginning time of the simulation.
• to: Duration of the simulation.
• zoom: If between 0 and 1, zoom out; if larger than 1, zoom in.

For example, the following command generates a svg image with the waveform from time 10 to time 20, and sets the zoom factor to 1.4. The -v option needs to be given before each variable.

$ vcd2svg -v from=10 -v to=20 -v zoom=1.4 clk data out 

Example

A unknown value (x) is drawn in the resulting svg file as a series of x characters. High-impedance state (z) is drawn as a horizontal line. The image below is a sample output from vcd2svg.

A svg image can be converted to png using inkscape:

$ inkscape -z -b "#00000000" --export-filename sim.png sim.svg

Bugs

• The width of the space for variable names is hardcoded to 100 pixels. This width can be insufficient for a variable with a long name.

• The label for the value of a variable may not fit in a wave pulse. For example, a hexadecimal label for a 64-bit value does not fit a pulse. Setting the zoom to a value slightly larger than 1 (such as 1.5) solves this.