.TH vvp 1 "March 25th, 2022" "" "Version %M.%n %E"
.SH NAME
vvp - Icarus Verilog vvp runtime engine

.SH SYNOPSIS
.B vvp
[\-inNsvV] [\-Mpath] [\-mmodule] [\-llogfile] inputfile [extended-args...]

.SH DESCRIPTION
.PP
\fIvvp\fP is the run time engine that executes the default compiled
form generated by Icarus Verilog. The output from the \fIiverilog\fP
command is not by itself executable on any platform. Instead, the
\fIvvp\fP program is invoked to execute the generated output file.

.SH OPTIONS
\fIvvp\fP accepts the following options:
.TP 8
.B -i
This flag causes all output to <stdout> to be unbuffered.
.TP 8
.B -l\fIlogfile\fP
This flag specifies a logfile where all MCI <stdlog> output goes.
Specify logfile as '\-' to send log output to <stderr>.  $display and
friends send their output both to <stdout> and <stdlog>.
.TP 8
.B -M\fIpath\fP
This flag adds a directory to the path list used to locate VPI
modules. The default path includes only the install directory for the
system.vpi module, but this flag can add other directories. Multiple
paths are allowed, and modules will be searched in order.
.TP 8
.B -m\fImodule\fP
Tell the vvp run time to load the named module before executing the
simulation. The \fBsystem.vpi\fP module is loaded by default, but
additional modules, including modules that you compiled locally, can
be specified with this flag. Any number of modules can be loaded, and
they will be linked in the order they are listed on the command line.

Normally, you only need to specify the name of the module, without any
directory path or .vpi suffix and the search path is scanned to find
the module. However, if the name includes at least one directory
character, then the search path is not scanned and the name is assumed
to be a complete file name.
.TP 8
.B -n
This flag makes $stop or a <Control\-C> a synonym for $finish.
It can be used to give the program a more meaningful interface when
running in a non-interactive environment.
.TP 8
.B -N
This flag does the same thing as \-n, but results in an exit code
of 1 if the stimulation calls $stop.  It can be used to indicate a
simulation failure when running a testbench.
.TP 8
.B -s
Stop. This will cause the simulation to stop in the beginning, before
any events are scheduled. This allows the interactive user to get
hold of the simulation just before it starts.
.TP 8
.B -v
Turn on verbose messages. This will cause information about run time
progress to be printed to standard out.
.TP 8
.B -V
Print the version of the runtime, and exit.

.SH EXTENDED ARGUMENTS
.PP
The vvp options described above must come before the design file name.
After the design file name, however, there may be any number of
unspecified arguments. These arguments are not interpreted by vvp but
are instead passed on to the executed design, and are available via
the \fI$test$plusargs\fP and \fI$value$plusargs\fP system functions.
.PP
Arguments that do not start with the plus(+) character are not
available to the \fI$plusargs\fP system tasks, but can still be
accessed via PLI code via the \fIvpi_get_vlog_info\fP function. This
means that vpi modules may use arguments that do not start with + and
be assured that they do not interfere with user defined plus-args.
.PP
There are a few extended arguments that are interpreted by the
standard system.vpi module, which implements the standard system tasks
and are always included. These arguments are described here.
.TP 8
.B -vcd
This extended argument sets the wave dump format to VCD. This is the
default in the absence of any \fBIVERILOG_DUMPER\fP environment
variable. The VCD dump files are large and ponderous, but are also
maximally compatible with third party tools that read waveform dumps.

.TP 8
.B -lxt\fR|\fP-lxt-speed\fR|\fP-lxt-space
These extended arguments set the wave dump format to lxt, possibly with
format optimizations. The \fB\-lxt\-space\fP flag sets the output
format to lxt with full compression enabled. The resulting files are
quite small. The \fB\-lxt\-speed\fP chooses the lxt compression mode
that leads to the best execution time and the fastest read time, at
the expense of some file size.

.TP 8
.B -lxt2\fR|\fP-lxt2-speed\fR|\fP-lxt2-space
.br
.ns
.TP
.B -lx2\fR|\fP-lx2-speed\fR|\fP-lx2-space
The LXT2 format is slower than LXT but usually takes less space, and
is written out incrementally. Thus, you can view lxt2 files while a
simulation is still running (or paused) or if your simulation crashes
or is killed, you still have a useful dump. The \fB\-lxt2\-speed\fP
or \fB\-lx2\-speed\fP arguments are the same as \fB\-lxt2\fP or
\fB\-lx2\fP. The \fB\-lxt2\-space\fP or \fB\-lx2\-space\fP arguments
enable better compression and turn off incremental writing.

.TP 8
.B -fst\fR|\fP-fst-speed\fR|\fP-fst-space
.br
.ns
.TP
.B -fst-space-speed\fR|\fP-fst-speed-space
This is a modern dumping format that is both faster and more compact
than the other dumping formats. It supports incremental dumping just
like \fB\-lxt2\fP. The \fB\-fst\-speed\fP argument uses a faster
compression methods that creates a noticeably larger output file.
The \fB\-fst\-space\fP argument performs a repack of the file on
close to produce the smallest possible dump file. The
\fB\-fst\-space\-speed\fP or \fB\-fst\-speed\-space\fP arguments
use the faster compression method and repack the file on close.

.TP 8
.B -none
This flag can be used by itself or appended to the end of the above
dumpers (vcd/lxt/lxt2/lx2/fst) to suppress all waveform output. This can
make long simulations run faster.

.TP 8
.B -sdf-warn
When loading an SDF annotation file, this option causes the annotator
to print warnings for questionable but non-fatal issues.

.TP 8
.B -sdf-info
When loading an SDF annotation file, this option causes the annotator
to print information about the annotation.

.TP 8
.B -sdf-verbose
This is shorthand for \-sdf\-info \-sdf\-warn.

.TP 8
.B -compatible
This extended argument enables improved compatibility with other
simulators. At present this only affects the display format for
real numbers when no format string is supplied.

.SH ENVIRONMENT
.PP
The vvp command also accepts some environment variables that control
its behavior. These can be used to make semi-permanent changes.

.TP 8
.B IVERILOG_DUMPER=\fIfst|lxt|lxt2|lx2|vcd|none\fP
This selects the output format for the waveform output. Normally,
waveforms are dumped in vcd format, but this variable can be used to
select lxt format, which is far more compact, though limited to
GTKWave or compatible viewers. It can also be used to suppress VCD
output, a time-saver for regression tests.

.TP 8
.B IVERILOG_VPI_MODULE_PATH=\fI/some/path:/some/other/path\fP
This adds additional components to the VPI module search path. Paths
specified in this way are searched after paths specified with \-M, but
before the default search path. Multiple paths can be separated with
colons (semicolons if using Windows).

.SH INTERACTIVE MODE
.PP
The simulation engine supports an interactive mode. The user may
interrupt the simulation (typically by typing <Control\-C>) to get to the
interactive prompt. From that prompt, the \fIhelp\fP command prints a
brief summary of the available commands.
.PP
The interactive mode may also be entered by a call to the \fI$stop\fP
system task from within the simulation, or by a call to the
\fIvpi_control\fP VPI function with the \fIvpiStop\fP control
argument. These means of entering interactive mode are equivalent.

.SH "AUTHOR"
.nf
Steve Williams (steve@icarus.com)

.SH SEE ALSO
iverilog(1),
iverilog\-vpi(1),
.BR "<http://iverilog.icarus.com/>"

.SH COPYRIGHT
.nf
Copyright \(co  2001\-2022 Stephen Williams

This document can be freely redistributed according to the terms of the
GNU General Public License version 2.0
