Why SystemVerilog Randomization Fails (and How to Debug It)
randomize() returned 0? Six causes of SystemVerilog randomization failure, how to read the VCS solver log, a 5-minute triage, and a demo with real logs.
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rand_mode vs constraint_mode in SystemVerilog: Freeze a Variable or Drop a Rule
In short: rand_mode() turns one random variable on or off. When it’s off, randomize() leaves that variable’s value alone. constraint_mode() turns one constraint block on or off. When it’s off, the solver ignores that rule. They are independent: freezing a variable does not switch off the constraints that use it, which is why randomize() often…