assert_time

Ensures that the value of a specified expression remains TRUE for a specified number of cycles after a start event.


	Parameters: severity_level num_cks action_on_new_start property_type msg coverage_level	Class: n-cycle assertion

Syntax

Parameters


	severity_level	Severity of the failure. Default: ‘OVL_ERROR.
	num_cks	Number of cycles after start_event is TRUE that test_expr must be held TRUE. Default: 1.
	action_on_new_start	Method for handling a new start event that occurs while a check is pending. Values are: ‘OVL_IGNORE_NEW_START, ‘OVL_RESET_ON_NEW_START and ‘OVL_ERROR_ON_NEW_START. Default: ‘OVL_IGNORE_NEW_START.
	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 (along with num_cks) identifies when to check test_expr.
	test_expr		Expression that should evaluate to TRUE for num_cks cycles after start_event initiates a check.

Description

The assert_time assertion checker checks the expression start_event at each rising edge of clk to determine whether or not to initiate a check. Once initiated, the check evaluates test_expr each rising edge of clk for num_cks cycles to verify that its value is TRUE. During that time, the assertion fails each cycle a sampled value of test_expr is not TRUE.

The method used to determine what constitutes a start event for initiating a check is controlled by the action_on_new_start parameter. If no check is in progress when start_event is sampled TRUE, a new check is initiated. But, if a check is in progress when start_event is sampled TRUE, the checker has the following actions:

The checker does not sample start_event for the next num_cks cycles after a start event.

The checker samples start_event every cycle. If a check is pending and the value of start_event is TRUE, the checker terminates the check and initiates a new check without sampling test_expr.

The checker samples start_event every cycle. If a check is pending and the value of start_event is TRUE, the assertion fails with an illegal start event violation. In this case, the checker does not initiate a new check, does not terminate a pending check and reports an additional assertion violation if test_expr is FALSE.

Assertion Checks


	ASSERT_TIME	The value of test_expr was not TRUE within num_cks cycles after start_event was sampled TRUE.
	illegal start event	The action_on_new_start parameter is set to ‘OVL_ERROR_ON_NEW_START and start_event expression evaluated to TRUE while the checker was monitoring test_expr.

Cover Points


	window_open	A time check was initiated.
	window_close	A time check lasted the full num_cks cycles.
	window_resets	The action_on_new_start parameter is ‘OVL_RESET_ON_NEW_START, and start_event was sampled TRUE while the checker was monitoring test_expr.

See also

Examples


assert_time #(
	‘OVL_ERROR, 3, ‘OVL_IGNORE_NEW_START, ‘OVL_ASSERT, “Error: invalid transaction”, ‘OVL_COVER_ALL)		// severity_level // num_cks // action_on_new_start // property_type // msg // coverage_level
	valid_transaction (
		clk, reset_n, req == 1, ptr >= 1 && ptr <= 3);	// clock // reset // start_event // test_expr

Ensures that ptr is sampled in the range 1 to 3 for three cycles after req is sampled equal to 1 at the rising edge of clk. If req is sampled equal to 1 when the checker samples ptr, a new check is not initiated (i.e., the new start is ignored).


assert_time #(
	‘OVL_ERROR, 3, ‘OVL_RESET_ON_NEW_START, ‘OVL_ASSERT, “Error: invalid transaction”, ‘OVL_COVER_ALL)		// severity_level // num_cks // action_on_new_start // property_type // msg // coverage_level
	valid_transaction (
		clk, reset_n, req == 1, ptr >= 1 && ptr <= 3);	// clock // reset // start_event // test_expr


assert_time #(
	‘OVL_ERROR, 3, ‘OVL_ERROR_ON_NEW_START, ‘OVL_ASSERT, “Error: invalid transaction”, ‘OVL_COVER_ALL)		// severity_level // num_cks // action_on_new_start // property_type // msg // coverage_level
	valid_transaction (
		clk, reset_n, req == 1, ptr >= 1 && ptr <= 3);	// clock // reset // start_event // test_expr

Ensures that ptr is sampled in the range 1 to 3 for three cycles after req is sampled equal to 1 at the rising edge of clk. If req is sampled equal to 1 when the checker samples ptr, the checker issues an illegal start event violation and does not start a new check.