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<li class="toctree-l1"><a class="reference internal" href="../../../releases/index.html">Icarus Verilog Release Notes</a><ul>
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<li class="toctree-l2"><a class="reference internal" href="../../../usage/simulation.html">Simulation Using Icarus Verilog</a></li>
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<li class="toctree-l2"><a class="reference internal" href="../../../usage/verilog_attributes.html">Verilog Attributes</a></li>
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<li class="toctree-l2"><a class="reference internal" href="../../../usage/ivlpp_flags.html">IVLPP - IVL Preprocessor</a></li>
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<li class="toctree-l2"><a class="reference internal" href="../../../usage/vvp_flags.html">VVP Command Line Flags</a></li>
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<li class="toctree-l2"><a class="reference internal" href="../../../usage/vhdlpp_flags.html">vhdlpp Command Line Flags</a></li>
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<li class="toctree-l2"><a class="reference internal" href="../../../usage/vpi.html">Using VPI</a></li>
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<li class="toctree-l2"><a class="reference internal" href="../../../usage/icarus_verilog_extensions.html">Icarus Verilog Extensions</a></li>
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<li class="toctree-l2"><a class="reference internal" href="../../../usage/icarus_verilog_quirks.html">Icarus Verilog Quirks</a></li>
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<li class="toctree-l1"><a class="reference internal" href="../../../targets/index.html">The Icarus Verilog Targets</a><ul>
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<li class="toctree-l2"><a class="reference internal" href="../../../targets/tgt-vvp.html">The vvp Code Generator (-tvvp)</a></li>
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<li class="toctree-l2"><a class="reference internal" href="../../../targets/tgt-null.html">The null Code Generator (-tnull)</a></li>
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<li class="toctree-l2"><a class="reference internal" href="../../../targets/tgt-vhdl.html">The VHDL Code Generator (-tvhdl)</a></li>
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<li class="toctree-l2"><a class="reference internal" href="../../../targets/tgt-vlog95.html">The Verilog ‘95 Code Generator (-tvlog95)</a></li>
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<li class="toctree-l2"><a class="reference internal" href="../../../targets/tgt-pcb.html">The PCB Code Generator (-tpcb)</a></li>
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<li class="toctree-l2"><a class="reference internal" href="../../../targets/tgt-fpga.html">The FPGA Code Generator (-tfpga)</a></li>
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<li class="toctree-l2"><a class="reference internal" href="../../../targets/tgt-pal.html">The PAL Code Generator (-tpal)</a></li>
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<li class="toctree-l2"><a class="reference internal" href="../../../targets/tgt-sizer.html">The sizer Code Analyzer (-tsizer)</a></li>
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<li class="toctree-l2"><a class="reference internal" href="../../../targets/tgt-verilog.html">The Verilog Code Generator (-tverilog)</a></li>
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<li class="toctree-l2"><a class="reference internal" href="../../../targets/tgt-blif.html">The BLIF Code Generator (-tblif)</a></li>
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<li class="toctree-l1 current"><a class="reference internal" href="../../index.html">Icarus Verilog Developer Support</a><ul class="current">
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<li class="toctree-l3 current"><a class="reference internal" href="index.html">VVP - Verilog Virtual Processor</a><ul class="current">
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<li class="toctree-l4 current"><a class="current reference internal" href="#">VPI Within VVP</a></li>
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<li class="toctree-l4"><a class="reference internal" href="vthread.html">Thread Details</a></li>
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<li class="toctree-l3"><a class="reference internal" href="../vpi/index.html">VPI in Icarus Verilog</a><ul>
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<li class="toctree-l4"><a class="reference internal" href="../vpi/vpi.html">VPI Modules in Icarus Verilog</a></li>
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<li class="toctree-l4"><a class="reference internal" href="../vpi/va_math.html">Verilog-A math library</a></li>
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<li class="toctree-l3"><a class="reference internal" href="../cadpli/cadpli.html">Cadence PLI1 Modules</a></li>
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<section id="vpi-within-vvp">
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<h1>VPI Within VVP<a class="headerlink" href="#vpi-within-vvp" title="Link to this heading">¶</a></h1>
|
||
<p>System tasks and functions in Verilog are implemented in Icarus
|
||
Verilog by C routines written with VPI. This implies that the vvp
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||
engine must provide at least a subset of the Verilog VPI
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||
interface. The minimalist concepts of vvp, however, make the method
|
||
less than obvious.</p>
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||
<p>Within a Verilog design, there is a more or less fixed web of
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||
vpiHandles that is the design database as is available to VPI
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||
functions. The Verilog standard defines quite a lot of types, but the
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||
vvp only implements the ones it needs. The VPI web is added into the
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||
design using special pseudo-ops that create the needed objects.</p>
|
||
<section id="loading-vpi-modules">
|
||
<h2>Loading VPI Modules<a class="headerlink" href="#loading-vpi-modules" title="Link to this heading">¶</a></h2>
|
||
<p>The vvp runtime loads VPI modules at runtime before the parser reads
|
||
in the source files. This gives the modules a chance to register tasks
|
||
and functions before the source is compiled. This allows the compiler
|
||
to resolve references to system tasks and system functions to a
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||
vpiHandle at compile time. References to missing tasks/function can
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||
thus be caught before the simulation is run.</p>
|
||
<blockquote>
|
||
<div><p>NOTE: This also, miraculously, allows for some minimal support of
|
||
the compiletf call. From the perspective of VPI code, compilation
|
||
of the VVP source is not unlike compilation of the original
|
||
Verilog.</p>
|
||
</div></blockquote>
|
||
<p>The handle that the vvp threads have to the VPI are the vpiHandles of
|
||
the system tasks and functions. The %vpi_call instruction, once compiled,
|
||
carries the vpiHandle of the system task.</p>
|
||
</section>
|
||
<section id="system-task-calls">
|
||
<h2>System Task Calls<a class="headerlink" href="#system-task-calls" title="Link to this heading">¶</a></h2>
|
||
<p>A system task call invokes a VPI routine, and makes available to that
|
||
routine the arguments to the system task. The called routine gets
|
||
access to the system task call by calling back the VPI requesting the
|
||
handle. It uses the handle, in turn, to get hold of the operands for
|
||
the task.</p>
|
||
<p>All that vvp needs to know about a system task call is the handle of
|
||
the system task definitions (created by the vpi_register_systf
|
||
function) and the arguments of the actual call. The arguments are
|
||
tricky because the list has no bound, even though each particular call
|
||
in the Verilog source has a specific set of parameters.</p>
|
||
<p>Since each call takes a fixed number of parameters, the input source
|
||
can include in the statement the list of arguments. The argument list
|
||
will not fit in a single generated instruction, but a vpiHandle that
|
||
refers to a vpiSysTfCall does. Therefore, the compiler can take the
|
||
long argument list and form a vpiSysTaskCall object. The generated
|
||
instruction then only needs to be a %vpi_call with the single parameter
|
||
that is the vpiHandle for the call.</p>
|
||
</section>
|
||
<section id="system-function-calls">
|
||
<h2>System Function Calls<a class="headerlink" href="#system-function-calls" title="Link to this heading">¶</a></h2>
|
||
<p>System function calls are similar to system tasks. The only
|
||
differences are that all the arguments are input only, and there is a
|
||
single magic output that is the return value. The same %vpi_call can
|
||
even be used to call a function.</p>
|
||
<p>System functions, like system tasks, can only be called from thread
|
||
code. However, they can appear in expressions, even when that
|
||
expression is entirely structural. The desired effect is achieved by
|
||
writing a wrapper thread that calls the function when inputs change,
|
||
and that writes the output into the containing expression.</p>
|
||
</section>
|
||
<section id="system-task-function-arguments">
|
||
<h2>System Task/Function Arguments<a class="headerlink" href="#system-task-function-arguments" title="Link to this heading">¶</a></h2>
|
||
<p>The arguments to each system task or call are not stored in the
|
||
instruction op-code, but in the vpiSysTfCall object that the compiler
|
||
creates and that the %vpi_call instruction ultimately refers to. All
|
||
the arguments must be some sort of object that can be represented by a
|
||
vpiHandle at compile time.</p>
|
||
<p>Arguments are handled at compile time by the parser, which uses the
|
||
argument_list rule to build a list of vpiHandle objects. Each argument
|
||
in the argument_list invokes whatever function is appropriate for the
|
||
token in order to make a vpiHandle object for the argument_list. When
|
||
all this is done, an array of vpiHandles is passed to code to create a
|
||
vpiSysTfCall object that has all that is needed to make the call.</p>
|
||
</section>
|
||
<section id="scopes">
|
||
<h2>Scopes<a class="headerlink" href="#scopes" title="Link to this heading">¶</a></h2>
|
||
<p>VPI can access scopes as objects of type vpiScope. Scopes have names
|
||
and can also contain other sub-scopes, all of which the VPI function
|
||
can access by the vpiInternalScope reference. Therefore, the run-time
|
||
needs to form a tree of scopes into which other scoped VPI objects are
|
||
placed.</p>
|
||
<p>A scope is created with a .scope directive, like so:</p>
|
||
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span><span data-line="1"><label> .scope "name" [, <parent>];
|
||
</span><span data-line="2"> .timescale <units>;
|
||
</span></pre></div>
|
||
</div>
|
||
<p>The scope takes a string name as the first parameter. If there is an
|
||
additional parameter, it is a label of the directive for the parent
|
||
scope. Scopes that have no parent are root scopes. It is an error to
|
||
declare a scope with the same name more than once in a parent scope.</p>
|
||
<p>The name string given when creating the scope is the basename for the
|
||
scope. The vvp automatically constructs full names from the scope
|
||
hierarchy, and runtime VPI code can access that full name with the
|
||
vpiFullName reference.</p>
|
||
<p>The .timescale directive changes the scope units from the simulation
|
||
precision to the specified precision. The .timescale directive affects
|
||
the current scope.</p>
|
||
<p>Objects that place themselves in a scope place themselves in the
|
||
current scope. The current scope is the one that was last mentioned by
|
||
a .scope directive. If the wrong scope is current, the label on a
|
||
scope directive can be used to resume a scope. The syntax works like
|
||
this:</p>
|
||
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span><span data-line="1">.scope <symbol>;
|
||
</span></pre></div>
|
||
</div>
|
||
<p>In this case, the <symbol> is the label of a previous scope directive,
|
||
and is used to identify the scope to be resumed. A scope resume
|
||
directive cannot have a label.</p>
|
||
</section>
|
||
<section id="variables">
|
||
<h2>Variables<a class="headerlink" href="#variables" title="Link to this heading">¶</a></h2>
|
||
<p>Reg vectors (scalars are vectors of length 1) are created by .var
|
||
statements in the source. The .var statement includes the declared
|
||
name of the variable, and the indices of the MSB and LSB of the
|
||
vector. The vpiHandle is then created with this information, and the
|
||
vpi_ipoint_t pointer to the LSB functor of the variable. VPI programs
|
||
access the vector through the vpiHandle and related functions. The VPI
|
||
code gets access to the declared indices.</p>
|
||
<p>The VPI interface to variable (vpiReg objects) uses the MSB and LSB
|
||
values that the user defined to describe the dimensions of the
|
||
object.</p>
|
||
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span><span data-line="1">/*
|
||
</span><span data-line="2"> * Copyright (c) 2001-2024 Stephen Williams (steve@icarus.com)
|
||
</span><span data-line="3"> *
|
||
</span><span data-line="4"> * This source code is free software; you can redistribute it
|
||
</span><span data-line="5"> * and/or modify it in source code form under the terms of the GNU
|
||
</span><span data-line="6"> * General Public License as published by the Free Software
|
||
</span><span data-line="7"> * Foundation; either version 2 of the License, or (at your option)
|
||
</span><span data-line="8"> * any later version.
|
||
</span><span data-line="9"> *
|
||
</span><span data-line="10"> * This program is distributed in the hope that it will be useful,
|
||
</span><span data-line="11"> * but WITHOUT ANY WARRANTY; without even the implied warranty of
|
||
</span><span data-line="12"> * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
||
</span><span data-line="13"> * GNU General Public License for more details.
|
||
</span><span data-line="14"> *
|
||
</span><span data-line="15"> * You should have received a copy of the GNU General Public License
|
||
</span><span data-line="16"> * along with this program; if not, write to the Free Software
|
||
</span><span data-line="17"> * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
|
||
</span><span data-line="18"> */
|
||
</span></pre></div>
|
||
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