assert_no_underflow


	Parameters: severity_level width min max 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. Width must be less than or equal to 32. Default: 1.
	min	Minimum value in the test range of test_expr. Default: 0.
	max	Maximum value in the test range of test_expr. Default: 2**width - 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 not change from a value of min to a value out of range or to a value equal to max.

Description

The assert_no_underflow assertion checker checks the expression test_expr at each rising edge of clk to determine if its value has changed from a value (at the previous rising edge of clk) that was equal to min. If so, the checker verifies that the new value has not underflowed min. That is, it verifies the value of test_expr is not less than min or greater than or equal to max (in which case, the assertion fails).

The checker is useful for verifying counters, where it can ensure the counter does not wrap from the lowest value to the highest value in a specified range. For example, it can be used to check that memory structure pointers do not wrap around. For a more general test for underflow, use assert_delta or assert_fifo_index.

Assertion Check


	ASSERT_NO_UNDERFLOW	Expression changed value from min to a value not in the range min + 1 to max - 1.

Cover Points


	test_expr_change	Expression changed value.
	test_expr_at_min	Expression evaluated to min.
	test_expr_at_max	Expression evaluated to max.

Errors

The parameters min and max must be specified such that min is less than or equal to max. Otherwise, the assertion fails on each tested clock cycle for which test_expr changed from max.

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_no_underflow #(
	‘OVL_ERROR, 3, 3, 7, ‘OVL_ASSERT, “Error: addr underflow”, ‘OVL_COVER_ALL)		// severity_level // width // min // max // property_type // msg // coverage_level
	addr_with_underflow (
		clk, reset_n, addr );	// clock // reset // test_expr