assert_next

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

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

Syntax

assert_next 
		[#(severity_level, num_cks, check_overlapping,  check_missing_start, property_type,  
		msg, coverage_level )] 
		instance_name (clk, reset_n, start_event, test_expr );

Parameters

 
severity_level
Severity of the failure. Default: ‘OVL_ERROR.
 
num_cks
Number of cycles after start_event is TRUE to wait to check that the value of test_expr is TRUE. Default: 1.
 
check_overlapping
Whether or not to perform overlap checking. Default: 1 (overlap checking off).
If set to 0, overlap checking is performed. From the rising edge of clk after start_event is sampled TRUE to the rising edge of clk of the cycle before test_expr is sampled for the current next check, the checker performs an overlap check. During this interval, if start_event is TRUE at a rising edge of clk, then the overlap check fails (illegal overlapping condition). The current next check continues but a new next check is not initiated.
If set to 1, overlap checking is not performed. A separate next check is initiated each time start_event is sampled TRUE (overlapping start events are allowed).
 
check_missing_start
Whether or not to perform missing-start checking. Default: 0 (missing-start checking off).
If set to 0, missing start checks are not performed.
If set to 1, missing start checks are performed. The checker samples test_expr every rising edge of clk. If the value of test_expr is TRUE, then num_cks rising edges of clk prior to the current time, start_event must have been TRUE (initiating a next check). If not, the missing-start check fails (start_event without test_expr).
 
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 num_cks cycles after start_event initiates a next check.

Description

The assert_next assertion checker checks the expression start_event at each rising edge of clk. If start_event is TRUE, a check is initiated. The check waits for num_cks cycles (i.e., for num_cks additional rising edges of clk) and evaluates test_expr. If test_expr is not TRUE, the assertion fails.

If overlap checking is off (check_overlapping is 1), additional checks can start while a current check is pending. If overlap checking is on, the assertion fails if start_event is sampled TRUE while a check is pending (except on the last clock).

If missing-start checking is off (check_missing_start is 0), test_expr can be TRUE any time. If missing-start checking is on, the assertion fails if test_expr is TRUE without a corresponding start event (num_cks cycles previously). However, if test_expr is TRUE in the interval of num_cks - 1 cycles after a reset and has no corresponding start event, the result is indeterminate (i.e., the missing-start check might or might not fail).

Assertion Checks

 
start_event without test_expr
The value of start_event was TRUE on a rising edge of clk, but num_cks cycles later the value of test_expr was not TRUE.
 
illegal overlapping condition detected
The check_overlapping parameter is set to 0 and start_event was TRUE on the rising edge of clk, but a previous check was pending.
 
test_expr without start_event
The check_missing_start parameter is set to 1 and start_event was not TRUE on the rising edge of clk, but num_cks cycles later test_expr was TRUE.
 
num_cks parameter<=0
The num_cks parameter is less than 2.

Cover Points

 
start_event
The value of start_event was TRUE on a rising edge of clk.
 
overlapping_start_events
The value of start_event was TRUE on a rising edge of clk while a check was pending.

See also

assert_change, assert_frame, assert_time, assert_unchange

Examples

  
assert_next #(
 
‘OVL_ERROR,
4,
1,
0,
‘OVL_ASSERT,
“error:”,
‘OVL_COVER_ALL)
// severity_level
// num_cks
// check_overlapping (off)
// check_missing_start (off)
// property_type
// msg
// coverage_level
 
valid_next_a_b (
 
 
 
clk,
reset_n,
a,
b );
// clock
// reset
// start_event
// test_expr
    

Ensures that b is TRUE 4 cycles after a is TRUE.

  
assert_next #(
 
‘OVL_ERROR,
4,
0,
0,
‘OVL_ASSERT,
“error:”,
‘OVL_COVER_ALL)
// severity_level
// num_cks
// check_overlapping (on)
// check_missing_start (off)
// property_type
// msg
// coverage_level
 
valid_next_a_b (
 
 
 
clk,
reset_n,
a,
b );
// clock
// reset
// start_event
// test_expr
    

Ensures that b is TRUE 4 cycles after a is TRUE. Overlaps are not allowed

  
assert_next #(
 
‘OVL_ERROR,
4,
1,
1,
‘OVL_ASSERT,
“error:”,
‘OVL_COVER_ALL)
// severity_level
// num_cks
// check_overlapping (off)
// check_missing_start (on)
// property_type
// msg
// coverage_level
 
valid_next_a_b (
 
 
 
clk,
reset_n,
a,
b );
// clock
// reset
// start_event
// test_expr
    

Ensures that b is TRUE 4 cycles after a is TRUE. Missing-start check is on.


  © Accellera Organization, Inc. 2005
All Rights Reserved.
Standard OVL V1.1a