48 lines
1.6 KiB
ReStructuredText
48 lines
1.6 KiB
ReStructuredText
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Icarus Verilog Quirks
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=====================
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This is a list of known quirks that are presented by Icarus Verilog. The idea
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of this chapter is to call out ways that Icarus Verilog differs from the
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standard, or from other implementations.
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This is NOT AN EXHAUSTIVE LIST. If something is missing from this list, let us
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know and we can add documentation.
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System Tasks - Unique to Icarus Verilog
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---------------------------------------
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These are system tasks that are unique to Icarus Verilog. Don't use any of
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these if you want to keep your code portable across other Verilog compilers.
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$readmempath
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^^^^^^^^^^^^
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The "$readmemb" and "$readmemh" system tasks read text files that contain data
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values to populate memories. Normally, those files are found in a current work
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directory. The "$readmempath()" system task can be used to create a search
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path for those files. For example:
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.. code-block:: verilog
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reg [7:0] mem [0:7];
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initial begin
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$readmemh("datafile.txt", mem);
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end
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This assumes that the "datafile.txt" is in the current working directory where
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the vvp command is running. But with the "$readmempath", one can specify a
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search path:
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.. code-block:: verilog
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reg [7:0] mem [0:7];
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initial begin
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$readmempath(".:alternative:/global/defaults");
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$readmemh("datafile.txt", mem);
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end
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In this example, the "datafile.txt" is searched for in each of the directories
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in the above list (separated by ":" characters). The first located instance
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is the one that is used. So for example, if "./datafile.txt" exists, then it
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is read instead of "/global/defaults/datafile.txt" even if the latter exists.
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