assert_one


	Parameters: severity_level width property_type msg coverage_level	Class: single-cycle assertion

Syntax

Parameters


	severity_level	Severity of the failure. Default: ‘OVL_ERROR.
	width	Width of the test_expr argument. Default: 32.
	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 evaluate to a one-hot value on the rising clock edge.

Description

The assert_one_hot assertion checker checks the expression test_expr at each rising edge of clk to verify the expression evaluates to a one-hot value. A one-hot value has exactly one bit set to 1.

The checker is useful for verifying control circuits, for example, it can ensure that a finite-state machine with one-hot encoding operates properly and has exactly one bit asserted high. In a datapath circuit the checker can ensure that the enabling conditions for a bus do not result in bus contention.

Assertion Checks


	ASSERT_ONE_HOT	Expression evaluated to zero or to a value with multiple bits set to 1.
	test_expr contains X/Z value	Expression evaluated to a value with an X or Z bit, and ‘OVL_XCHECK_OFF is not set.

Cover Points


	all_one_hots_checked	Expression evaluated to all possible combinations of one-hot values.
	test_expr_change	Expression has changed value.

Notes

1. By default, the assert_one_hot assertion is optimistic and the assertion fails if test_expr is zero or has multiple bits not set to 0 (i.e.equals 1, X, Z, etc.). However, if ‘OVL_XCHECK_OFF is set, the ASSERT_ONE_HOT assertion fails if and only if test_expr is zero or has multiple bits that are 1.

assert_one_hot #(
	‘OVL_ERROR, 4, ‘OVL_ASSERT, “Error: sel not one-hot”, ‘OVL_COVER_ALL)		// severity_level // width // property_type // msg // coverage_level
	valid_sel_one_hot (
		clk, reset_n, sel );	// clock // reset // test_expr

assert_one_hot