[sv-ac] Mantis 2008: Glitches and Unique/Priority constructs (was in 2005)

Hi Erik,


I have been thinking about the issue of glitches and the Unique/Priority
constructs.

I think that the proper way to fix this is to change the syntax of the unique
and priority constructs to allow for a event to serve as a clocking mechanism
for example:

	unique (@posedge clk) case (a)

		0,1: $display("0 or 1");
		2: $display("2");
		4: $display("4");
	endcase

The clocking event would allow the unique or priority assertions to be treated
as concurrent assertions that are clocked by a reasonable clock.  The real
problem is when these constructs appear in an always_comb block.  An always_ff
block is not going to have the same glitch problem.  But to create a
concurrent assertion in an always_comb block, you'll need a clock.
Otherwiase, You'll have to create some equivalent clock that ticks every
simulation time step, and that will kill simulation performance.

Tom

-- 
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Thomas J. Thatcher
Sun Microsystems
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