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Commentary on traces (#2925)

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This commit is contained in:
Wilson Snyder 2021-05-13 18:56:07 -04:00
parent 3718fe1ca1
commit 88fed4bc2f
3 changed files with 12 additions and 6 deletions
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14
docs/guide/faq.rst
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@ -118,9 +118,9 @@ A. Pass the :vlopt:`--trace` option to Verilator, and in your top level C
B. Or, for finer-grained control, or C++ files with multiple Verilated
modules you may also create the trace purely from C++. Create a
VerilatedVcdC object, and in your main loop call
``trace_object->dump(time)`` every time step, and finally call
``trace_object->close()``.
VerilatedVcdC object, and in your main loop right after ``eval()`` call
``trace_object->dump(contextp->time())`` every time step, and finally
call ``trace_object->close()``.
.. code-block:: C++
:emphasize-lines: 1,5-8,12
@ -128,15 +128,17 @@ B. Or, for finer-grained control, or C++ files with multiple Verilated
#include "verilated_vcd_c.h"
...
int main(int argc, char** argv, char** env) {
const std::unique_ptr<VerilatedContext> contextp{new VerilatedContext};
...
Verilated::traceEverOn(true);
VerilatedVcdC* tfp = new VerilatedVcdC;
topp->trace(tfp, 99); // Trace 99 levels of hierarchy
tfp->open("obj_dir/t_trace_ena_cc/simx.vcd");
...
while (Verilated::time() < sim_time && !Verilated::gotFinish()) {
Verilated::timeInc(1);
tfp->dump(main_time);
while (contextp->time() < sim_time && !contextp->gotFinish()) {
contextp->timeInc(1);
topp->eval();
tfp->dump(contextp->time());
}
tfp->close();
}

2
include/verilated_fst_c.h
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@ -152,6 +152,8 @@ public:
/// Flush dump
void flush() VL_MT_SAFE { m_sptrace.flush(); }
/// Write one cycle of dump data
/// Call with the current context's time just after eval'ed,
/// e.g. ->dump(contextp->time())
void dump(vluint64_t timeui) { m_sptrace.dump(timeui); }
/// Write one cycle of dump data - backward compatible and to reduce
/// conversion warnings. It's better to use a vluint64_t time instead.

2
include/verilated_vcd_c.h
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@ -368,6 +368,8 @@ public:
/// Flush dump
void flush() VL_MT_SAFE { m_sptrace.flush(); }
/// Write one cycle of dump data
/// Call with the current context's time just after eval'ed,
/// e.g. ->dump(contextp->time())
void dump(vluint64_t timeui) VL_MT_SAFE { m_sptrace.dump(timeui); }
/// Write one cycle of dump data - backward compatible and to reduce
/// conversion warnings. It's better to use a vluint64_t time instead.