assert_win_unchange

Ensures that the value of a specified expression does not change in a specified window between a start event and an end event.


	Parameters: severity_level width property_type msg coverage_level	Class: event-bounded assertion

Syntax

Parameters


	severity_level	Severity of the failure. Default: ‘OVL_ERROR.
	width	Width of the test_expr argument. 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.
start_event		Expression that opens an event window.
test_expr	[ width - 1: 0 ]	Expression that should not change value in the event window
end_event		Expression that closes an event window.

Description

The assert_win_unchange assertion checker checks the expression start_event at each rising edge of clk to determine if it should open an event window at the start of the next cycle. If start_event is sampled TRUE, the checker evaluates test_expr. At each subsequent rising edge of clk, the checker evaluates end_event and re-evaluates test_expr. If a sampled value of test_expr is changed from its value in the previous cycle, then the assertion fails. If end_event is TRUE, the checker closes the event window and returns to the state of monitoring start_event at the next rising edge of clk.

The checker is useful for ensuring certain variables and expressions do not change in various event windows. A typical use is to verify that synchronization logic responds after a stimulus (for example, bus transactions occurs without interrupts or write commands are not issued during read cycles). Another typical use is to verify that non-deterministic multiple-cycle operations with enabling conditions function properly with the same data.

Assertion Check


	ASSERT_WIN_UNCHANGE	The test_expr expression changed value during an open event window.

Cover Points


	window_open	An event window opened (start_event was TRUE).
	window_close	An event window closed (end_event was TRUE in an open event window).

assert_win_unchange #(
	‘OVL_ERROR, 8, ‘OVL_ASSERT, “Error: a changed during divide”, ‘OVL_COVER_ALL)		// severity_level // width // property_type // msg // coverage_level
	valid_div_win_unchange_a (
		clk, reset_n, start, a, done);	// clock // reset // start_event // test_expr // end_event