assert_decrement

Ensures that the value of a specified expression changes only by the specified decrement value.


	Parameters: severity_level width value property_type msg coverage_level	Class: 2-cycle assertion

Syntax

Parameters


	severity_level	Severity of the failure. Default: ‘OVL_ERROR.
	width	Width of the test_expr argument. Default: 1.
	value	Decrement value for test_expr. Default: 1.
	property_type	Property type. Default: ‘OVL_ASSERT.
	msg	Error message printed when assertion fails. Default: “VIOLATION”.
	coverage_level	Coverage level. Default: ‘OVL_COVER_ALL.

Ports


clk		Clock event for the assertion. The checker samples on the rising edge of the clock.
reset_n		Active low synchronous reset signal indicating completed initialization.
test_expr	[ width - 1: 0 ]	Expression that should decrement by value whenever its value changes from the rising edge of clk to the next rising edge of clk.

Description

The assert_decrement assertion checker checks the expression test_expr at each rising edge of clk to determine if its value has changed from its value at the previous rising edge of clk. If so, the checker verifies that the new value equals the previous value decremented by value. The checker allows the value of test_expr to wrap, if the total change equals the decrement value. For example, if width is 5 and value is 4, then the following change in test_expr is valid:

The checker is useful for ensuring proper changes in structures such as counters and finite-state machines. For example, the checker is useful for circular queue structures with address counters that can wrap. Do not use this checker for variables or expressions that can increment. Instead consider using the assert_delta checker.

Assertion Check


	ASSERT_DECREMENT	Expression evaluated to a value that is not its previous value decremented by value.

Cover Point


	test_expr_change	Expression changed value.

Notes

1. The assertion check compares the current value of test_expr with its previous value. Therefore, checking does not start until the second rising clock edge of clk after reset_n deasserts.

assert_decrement #(
	‘OVL_ERROR, 4, 1, ‘OVL_ASSERT, “Error: invalid binary decrement”, ‘OVL_COVER_ALL)		// severity_level // width // value // property_type // msg // coverage_level
	valid_count (
		clk, reset_n, count );	// clock // reset // test_expr