assert_one

Ensures that the value of a specified expression is one-cold (or equals an inactive state value, if specified).


	Parameters: severity_level width inactive 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.
	inactive	Inactive state of test_expr: ‘OVL_ALL_ZEROS, ‘OVL_ALL_ONES or ‘OVL_ONE_COLD. Default: ‘OVL_ONE_COLD.
	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-cold or inactive value on the rising clock edge.

Description

The assert_one_cold assertion checker checks the expression test_expr at each rising edge of clk to verify the expression evaluates to a one-cold or inactive state value. A one-cold value has exactly one bit set to 0. The inactive state value for the checker is set by the inactive parameter. Choices are: ‘OVL _ALL_ZEROS (e.g., 4‘b0000), ‘OVL_ALL_ONES (e.g.,4‘b1111) or ‘OVL_ONE_COLD. The default inactive parameter value is ‘OVL_ONE_COLD, which indicates test_expr has no inactive state (so only a one-cold value is valid for each check).

The checker is useful for verifying control circuits, for example, it can ensure that a finite-state machine with one-cold encoding operates properly and has exactly one bit asserted low. 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_COLD	Expression assumed an active state with multiple bits set to 0.
	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_colds_checked	Expression evaluated to all possible combinations of one-cold values.
	test_expr_all_zeros	Expression evaluated to the inactive state and the inactive parameter was set to ‘OVL_ALL_ZEROS.
	test_expr_all_ones	Expression evaluated to the inactive state and the inactive parameter was set to ‘OVL_ALL_ONES.
	test_expr_change	Expression has changed value.

Notes

1. By default, the assert_one_cold assertion is pessimistic and the assertion fails if test_expr is active and multiple bits are not 1 (i.e.equals 0, X, Z, etc.). However, if ‘OVL_XCHECK_OFF is set, the assertion fails if and only if test_expr is active and multiple bits are 0.

See also

Examples


assert_one_cold #(
	‘OVL_ERROR, 4, ‘OVL_ONE_COLD, ‘OVL_ASSERT, “Error: sel_n not one-cold”, ‘OVL_COVER_ALL)		// severity_level // width // inactive (no inactive state) // property_type // msg // coverage_level
	valid_sel_n_one_cold (
		clk, reset_n, sel_n );	// clock // reset // test_expr


assert_one_cold #(
	‘OVL_ERROR, 4, ‘OVL_ALL_ONES, ‘OVL_ASSERT, “Error: sel_n not one-cold or inactive”, ‘OVL_COVER_ALL)		// severity_level // width // inactive // property_type // msg // coverage_level
	valid_sel_n_one_cold (
		clk, reset_n, sel_n );	// clock // reset // test_expr

Ensures that sel_n is one-cold or inactive (4’b1111) at each rising edge of clk.


assert_one_cold #(
	‘OVL_ERROR, 4, ‘OVL_ALL_ZEROS, ‘OVL_ASSERT, “Error: sel_n not one-cold”, ‘OVL_COVER_ALL)		// severity_level // width // inactive // property_type // msg // coverage_level
	valid_sel_n_one_cold (
		clk, reset_n, sel_n );	// clock // reset // test_expr

Ensures that sel_n is one-cold or inactive (4’b0000) at each rising edge of clk.