In short: A constraint override happens when a child class declares a constraint with the same name as one in its parent. The child version replaces the parent version, so the solver uses only the child rule. If instead the child uses a different name, both constraints stay active and must be satisfied together, and…
In short: The class method randomize() assigns random values to the rand and randc members of an object, using that class’s constraints. The scope function std::randomize() does the same job but for plain variables in the current scope, with no class needed. Use randomize() when your random data lives in a class with reusable constraints;…
In short: A randc variable walks through every value in its range once before any value repeats. You can copy that no repeat behaviour with a plain rand variable by keeping a list of values already produced and adding a constraint that excludes them. In post_randomize() you push the new value onto the list; a…
In short: To fill an array with values that never repeat, mark the array rand and add one line: constraint c { unique {arr}; }. The solver then gives every element a different value. On an old simulator that doesn’t know unique, use a nested foreach with !=. And if you don’t need the solver…
In short: When you need an array of distinct values in a mixed order but do not need full randomness, you can skip constraints. Fill the array with known distinct values, such as the index itself, then call the built in shuffle() method to rearrange them. The result has no repeats and a random order,…
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…
In short: To enable or disable one specific constraint, call constraint_mode() on the named block, not on the whole object: obj.block_name.constraint_mode(0) switches that one rule off, and obj.block_name.constraint_mode(1) switches it back on. Every other constraint keeps working. Called with no argument on a named block it returns the current state, 1 for enabled and 0…
In short: randcase picks one branch at random using weights: each branch weight divided by the sum of all weights is its chance of being taken. randsequence is bigger; it builds structured sequences from named productions, so it can produce ordered or branching stimulus such as instruction streams. Use randcase for a quick weighted choice…
In short: Both @(e) and wait(e.triggered) pause a process until event e fires, but they treat timing differently. @(e) is edge-sensitive: the process must already be blocked on it before the trigger, or it misses the event. wait(e.triggered) is level-sensitive within the current time step: it still catches the event even if the trigger happened…
In short: A mailbox in SystemVerilog is a built in class that lets two parallel processes pass data safely, like a FIFO with a producer on one side and a consumer on the other. The producer calls put() to add an item and the consumer calls get() to take one. put() and get() block when…
