SystemC VCD trace does not set correct precision #62
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Original Redmine Comment SpTraceVcdCFile is for C files, while SpTraceVcdFile is for SystemC. I'll clarify the docs. |
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Original Redmine Comment Ah thanks - my misunderstanding from reading the example in the distribution. I've tried, but can't see how to use @SpTraceFile@ to assist in SystemC tracing (the class I referred to as @SpTraceVcdFile@ is in fact @SpTraceFile@). This is a subclass of the abstract class @sc_trace@ used to do SystemC tracing. However I can't see how to use it. There should be an alternative to @sc_create_vcd_trace_file@ to create instances, which I can't find. I also ran into issues when I tried including the header @"SpTraceVcd.h"@, it got upset if I included it after any of the @"Vxxxx.h"@ headers. Really I don't really want to do SystemC tracing - it's the underlying Verilog signals I'm after, so my approach was correct, but since I'm in the C world, I need to set the precision. From my past experience, this is the usual scenario - it's the underlying signals that need to be traced. An option to allow Verilator to do this and automatically pick up the SystemC time precision would be a nice enhancement for the future. |
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Original Redmine Comment I looked at doing this again, and it makes a bit as a mess as the C tracing isn't at all systemc aware, and making it so breaks compiles when there's no systemc. So until a major tracing rewrite comes I'll need to punt. Sorry. |
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resolution: wontfix
Author Name: Jeremy Bennett (@jeremybennett)
Original Redmine Issue: 62 from https://www.veripool.org
Original Date: 2009-01-27
Use of the SpTraceVCD functions does not appear to set the trace precision correctly.
When creating an instance of @SpTraceVcdCFile@, the time resolution is held in the associated @SpTraceVcd@ object (private variable @m_timeRes@, which can be set by the @set_time_precision()@ function). This defaults to 10e-9 (1ns), which is inconsistent with SystemC's default of 10e-12 (1ps). It can be overridden by explicitly, e.g:
Really this should be set automatically in a SystemC environment by calling the underlying @sc_get_time_precision()@ function from the constructor of @SpTraceVcdCFile@. The code to do this exists in the class @SpTraceVcdFile@, but I cannot see that this class is currently used.
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