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ivtest: pr1002: Avoid race condition 

The pr1002 test has a always block with the `dataout` in its sensitivity
list. It compares `dataout` to `expected_dataout`.

Both `dataout` and `expected_dataout` depend on `datain` and are updated in
the same cycle. This means there is no guarantee in which order they are
updated and the always block might get scheduled before `expected_dataout`
has been updated. This can lead to a test failure.

To avoid this slightly change the test to use a task to perform the
comparison and add an explicit delay before the task is executed so that
all updates have a chance to be fully resolved

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
This commit is contained in:
Lars-Peter Clausen 2024-01-07 10:17:10 -08:00
parent 9b1ac6ab50
commit 2d611c4347
1 changed files with 28 additions and 19 deletions
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47
ivtest/ivltests/pr1002.v
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@ -8,29 +8,11 @@ assign dataout = datain >>> 2;
reg test_failed;
initial
begin
test_failed = 0;
#1 datain = 14'h0FFF;
#1 datain = 14'h0000;
#1 datain = 14'h1FFF;
#1 datain = 14'h1000;
#1 datain = 14'h2FFF;
#1 datain = 14'h2000;
#1 datain = 14'h3FFF;
#1 datain = 14'h3000;
#2;
if (test_failed)
$display("TEST FAILED :-(");
else
$display("TEST PASSED :-)");
end
wire signed [15:0] expected_dataout;
assign expected_dataout = ($signed({datain[13:2], 2'b0}) / 4) ;
always @(dataout)
task check_data;
if (expected_dataout != dataout)
begin
$display("datain = %d dataout = %h expected = %h ... CHECK FAILED", datain, dataout, expected_dataout);
@ -38,5 +20,32 @@ always @(dataout)
end
else
$display("datain = %d dataout = %d expected = %d ... CHECK PASSED", datain, dataout, expected_dataout);
endtask
initial
begin
test_failed = 0;
#1 datain = 14'h0FFF;
#0 check_data; // #0 delay to allow the wire to resolve
#1 datain = 14'h0000;
#0 check_data;
#1 datain = 14'h1FFF;
#0 check_data;
#1 datain = 14'h1000;
#0 check_data;
#1 datain = 14'h2FFF;
#0 check_data;
#1 datain = 14'h2000;
#0 check_data;
#1 datain = 14'h3FFF;
#0 check_data;
#1 datain = 14'h3000;
#0 check_data;
#2;
if (test_failed)
$display("TEST FAILED :-(");
else
$display("TEST PASSED :-)");
end
endmodule // top