65 lines
2.1 KiB
Verilog
65 lines
2.1 KiB
Verilog
/*
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* Copyright (c) 2001 Stephen Williams (steve@icarus.com)
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*
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* This source code is free software; you can redistribute it
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* and/or modify it in source code form under the terms of the GNU
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* General Public License as published by the Free Software
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* Foundation; either version 2 of the License, or (at your option)
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* any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
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*/
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/*
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* This program demonstrates a tricky aspect of the Verilog syntax.
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* The problem is with the repeat statement. In fact, there is a
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* question as to whether it is a repeat statement at all, or an
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* event statement with a repeat modifier. These are the possibilities:
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*
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* procedural_timing_control_statement ::=
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* delay_or_event_control statement_or_null
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*
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* delay_or_event_control ::=
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* event_control
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* | repeat ( expression ) event_control
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*
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* If this interpretation is used, then ``repeat (5) @(posedge clk)''
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* should be taken as a delay_or_event_control and the thread will
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* block until the 5th clk posedge.
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*
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* loop_statement ::=
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* repeat ( expression ) statement
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*
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* If *this* interpretation is used, then ``repeat (5)'' is the loop
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* head is used and the statement in the example is executed 5 times.
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*
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* These two interpretations both appear to be perfectly valid. However,
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* real tools use the loop_statement, so the standard must be considered
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* broken and this interpretation used.
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*/
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module main;
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reg clk = 1;
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always #5 clk = ~clk;
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initial #1
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repeat (5) @(posedge clk) begin
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if ($time !== 10) begin
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$display("FAILED -- $time = %t", $time);
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$finish;
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end
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$display("PASSED");
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$finish;
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end
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endmodule // main
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