API for VHDL Assert Statements

Proposal Editing Information

• Who Updates: JimLewis, <Add YourName >, ...
• Date Proposed: 2012-08-17
• Date Last Updated: 2012-08-17
• Priority:
• Complexity:
• Focus: Testbench
• Proposal Maturity: Brainstorming

Requirement Summary

Add subprograms and attributes for VHDL assert statements that allow enabling/disabling assert statements as well as getting a count of assert statements

Rationale

Feedback for testbench usage.

Related Issues: PSL Attributes

Will want to keep API consistent.

Proposal

Assert Attributes

Suggested to keep a strong correspondence with VHDL ASSERT with PSL ASSERT. May not be necessary since there are other ways to program this functionality. Requires the assert to have a statement label.

A'TRANSACTION

The intent is to be able to trigger a process when a labeled VHDL assert evalutates to true.

Kind: Signal.
Prefix: A VHDL assert statement with the static label A.
Result type: Type BIT. 
Result: A signal whose value toggles to the inverse of its previous value in each 
simulation cycle in which a VHDL assert statement is true. 
Restrictions: A description is erroneous if it depends on the initial value of A'TRANSACTION. 

A'EVENT

If multiple different VHDL ASSERT statements trigger a process, this one allows us to detect which one triggered the process

Kind: Function.
Prefix: A VHDL assert statement with the static label A. 
Result type: Type BOOLEAN.
Result: A value TRUE during each simulation cycle in which a VHDL assert statement is true.

A'COUNT

Allows a count of specific VHDL assert statement to be accessed.

Kind: Function.
Prefix: A VHDL assert statement with the static label A. 
Result type: Type INTEGER.
Result: The number of times a VHDL assert statement evaluated to true.

ASSERT API - Predefined Functions

?? replace level with an array of level values?

Add turn on/off printing of the severity_level value

The following is preliminary ideas on a control interface for VHDL ASSERT statements.

type HIER_LEVEL_TYPE is (CURRENT, BELOW) ;

HIER parameter specifies if the command applies the the current level of hierarchy or current level plus below.

PATH parameter specifies the path in a consistent manner with external name specifications.

ASSERT_IGNORE

procedure ASSERT_IGNORE(LEVEL : SEVERITY_LEVEL := NOTE; PATH : STRING := "/" ; HIER : HIER_LEVEL_TYPE := BELOW) ;

Enables VHDL ASSERT statements within the scope of path.

Intent: Give VHDL control to which assertions print and which get ignored.

ASSERT_ENABLE

procedure ASSERT_ENABLE(LEVEL : SEVERITY_LEVEL := NOTE; PATH : STRING := "."; HIER : HIER_LEVEL_TYPE := CURRENT) ;

Enables VHDL ASSERT statements within the scope of path.

Intent: Turn assertions on - such as after the design enters reset.

ASSERT_DISABLE

procedure ASSERT_DISABLE(LEVEL : SEVERITY_LEVEL := NOTE; PATH : STRING := "/"; HIER : HIER_LEVEL_TYPE := BELOW) ;

Disables VHDL ASSERT statements within the scope of path.

Intent: Turn assertions off - such as before the design enters reset.

ASSERT_STOP

procedure ASSERT_STOP(LEVEL : SEVERITY_LEVEL := ERROR; PATH : STRING := "/" ; HIER : HIER_LEVEL_TYPE := BELOW) ;

Enables VHDL ASSERT statements within the scope of path.

Intent: Give VHDL control to which assertions cause a simulation to stop. Default level in the language is failure. Allows it to be set for the entire design or a specific design.

READ_STOP

procedure READ_STOP(ENABLE : Boolean := TRUE ; PATH : STRING := "/" ; HIER : HIER_LEVEL_TYPE := BELOW) ;

Intent: Give VHDL control to what happens during a textio read error. Language currently reports the error and continues with an invalid read value. READ_STOP with defaults will cause unhandled texio read errors (those generated by the read procedure with two parameters) will cause the simulator to stop (like std.env.stop).

ASSERT_FORMAT

procedure ASSERT_FORMAT(format : string) ; procedure ASSERT_FORMAT(severity : severity_level; format: string) ;

String parameter designates format of assertion. For example (inspired by: inspired by slide 44):

ASSERT_FORMAT("** %S: %R" & LF & "  Time: %T Iteration: %D Instance: %I");
...
report "Yikes!" severity failure ;

Creates something similar to simulator defaults:

** FAILURE: Yikes!
    Time: 217600 ns Iteration: 0 Instance: /tb_top

The following modifies the output to one line:

ASSERT_FORMAT("** %S: %R    at %T    in: %I");
...
report "Yikes!" severity failure ;

Creates something similar to simulator defaults:

** FAILURE: Yikes!    at 217600 ns    in: /tb_top

ASSERT_TOTAL_COUNT

function ASSERT_TOTAL_COUNT(LEVEL : SEVERITY_LEVEL := NOTE; PATH : STRING := ".") return natural;

Returns the total number of times VHDL assert statements triggered during a simulation.

Intent: Effectively an error count value due to assert statements.

ASSERT_COUNT

function ASSERT_COUNT(LEVEL : SEVERITY_LEVEL := NOTE; PATH : STRING := ".") return natural;

Returns the number of VHDL assert statements that have triggered at least once during a simulation

Intent: When Coupled with ASSERT_GET_NAME enables identification of all assertions that have triggered during this simulation.

ASSERT_GET_NAME

function ASSERT_GET_NAME(LEVEL : SEVERITY_LEVEL := NOTE; N : INTEGER := 1 ; PATH : STRING := ".") return natural;

Returns the string value of the label of the N'th PSL assert statement whose a count greater than the 0. The PATH parameter specifies the path of the design.

Intent: When Coupled with ASSERT_COUNT enables identification of all assertions that have triggered during this simulation.

Use Models

Questions

Enable/Disable functionality - one procedure with parameters or two procedures

Enable/Disable functionality - how to handle hierarchy below the current level?

General Comments

Need a way to count and disable errors generated by testbenches so we can produce pass/fail messages when a test completes.

How about just in std.env we put

function get_assert_count(sev : severity_level := WARNING) return natural;

That would report the number of any counts of level "sev" or above of any 1) failed asserts or 2) reports.

-- RobGaddi - 2016-03-31

Supporters

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-- JimLewis - 2014-12-04