Re: [sv-ac] Fwd: sv-ac: virtual interface application example

Manisha,
2. Using class variables in clock expression. Currently usage of class
variables in clock expressions is not well defined. In your example, the
expect needs to be explicitly clocked (it does not infer clock). We have
seen usage of class variables in clock expressions earlier and I filed a
mantis item (001513: LRM does not clarify if class variables can be used in
clock expressions under SV-EC). Here is something from LRM which prohibits
use of virtual interface in sensitivity lists. If we use virtual interface
in the clock expression for expect, we are effectively using it in
sensitivity list:

Once a virtual interface has been initialized, all the components of the
underlying interface instance are
directly available to the virtual interface via the dot notation. These
components can only be used in
procedural statements; they cannot be used in continuous assignments or
sensitivity lists

[Ben] I sort of disagree that If we use virtual interface in the clock
expression for expect, we are effectively using it in sensitivity list:, The
LRM that you quote just says that the following is illegal:
  assign some_virutal_if.w = some_virutal_if.q;
 always (@ some_virutal_if.w) ???? Illegal But per LRM
example ???
 *task wait_for_bus(); // wait for the bus to be granted*
*@(posedge bus.grant); [Ben] Isn't that a sensitivity
list? *
*endtask*

Can I get some clarification as to why the LRM example *@(posedge
bus.grant); is legal ?*
Ben
On Wed, Jun 23, 2010 at 1:08 AM, Kulshrestha, Manisha <
Manisha_Kulshrestha@mentor.com> wrote:

> Hi Ben,
>
> There are few issues here that we need to address.
>
> 1. The virtual interface is attached to an instance of a class (or class
> object). So, different class objects (of the same class) can have different
> interface objects attached to them. Even same class object can refer to
> different virtual interfaces at different times. It is possible that in the
> middle of execution of expect (while it is waiting), the virtual interface
> object changes.
> Here is some text from LRM:
>
> Virtual interface variables may be passed as arguments to tasks, functions,
> or methods. A single virtual interface variable can thus represent different
> interface instances at different times throughout the simulation. A virtual
> interface shall be initialized before referencing a component of the virtual
> interface; it has the value *null *before it is initialized. Attempting to
> use a *null *virtual interface shall result in a fatal run-time error.
>
>
> 2. Using class variables in clock expression. Currently usage of class
> variables in clock expressions is not well defined. In your example, the
> expect needs to be explicitly clocked (it does not infer clock). We have
> seen usage of class variables in clock expressions earlier and I filed a
> mantis item (001513: LRM does not clarify if class variables can be used
> in clock expressions under SV-EC). Here is something from LRM which
> prohibits use of virtual interface in sensitivity lists. If we use virtual
> interface in the clock expression for expect, we are effectively using it in
> sensitivity list:
>
> Once a virtual interface has been initialized, all the components of the
> underlying interface instance are
> directly available to the virtual interface via the dot notation. These
> components can only be used in
> procedural statements; they cannot be used in continuous assignments or
> sensitivity lists.
>
> 2. Usage of automatic variables in expect. Although LRM currently allows
> usage of automatic variables in expect, the assumption is that the automatic
> variable will not change in the middle of execution of expect. Even
> procedural concurrent assertions are allowed to use automatic variables but
> they are considered constants. The value of these variables is captured at
> the time of attempt and the same value is used through out the evaluation of
> that attempt. Is that how you see the usage of automatic signals in your
> example, or you would like the expect to use the latest values.
>
>
> Thanks.
> Manisha
>
> ------------------------------
> *From:* owner-sv-ac@eda.org [mailto:owner-sv-ac@eda.org] *On Behalf Of *ben
> cohen
> *Sent:* Wednesday, June 23, 2010 3:29 AM
> *To:* Eduard Cerny; sv-ac@eda.org; Korchemny, Dmitry
> *Subject:* Re: [sv-ac] Fwd: sv-ac: virtual interface application example
>
> Ed,
> That particular example is from my VMM book, and does not use the expect.
> Here are 2 examples; One with a modification that could use the expect, and
> another example.
> class Fifo_cmd_xactor extends vmm_xactor;
> *virtual fifo_if.fdrvr_if_mp f_if;*
> * virtual fifo_if.fslave_if_mp s_if; *
> ...
> function new(...
> virtual fifo_if.fdrvr_if_mp new_vir_if,
> virtual fifo_if.fslave_if_mp new_svir_if;
> ... );
> *this.f_if = new_vir_if;*
> * this.s_if = new_svir_if; *
> ...
> endfunction : new
> endclass: Fifo_cmd_xactor
>
> task Fifo_cmd_xactor::push_task (word_t data);
> * @ ( f_if.driver_cb);*
> * expect (s_if.xxx ##[1:5} s_if.yyy); // <----*
> * f_if.driver_cb.data_in <= data;*
> * f_if.driver_cb.push <= 1'b1;*
> * f_if.driver_cb.pop <= 1'b0;*
> * **@ ( f_if.driver_cb);*
> * f_if.driver_cb.push <= 1'b0;*
> * *
> endtask : push_task
>
> // NEW EXAMPLE with Action Blocks
> However, here is another example
> class mst_bfm; // driver class
> * virtual master_if.fdrvr_if_mp v_if;*
> function new( …
> *virtual master_if.fdrvr_if_mp new_vir_if, ..);*
> this.v_if = new_vir_if;
> ..
> endfunction : new
> …
> task continue2() .. endtask : continue2 // What to do if response to abort
> is the ABORTED
> task abort_error(); … endtask : abort_error // What to do if response to
> abort is not ABORTED
> *task driver(pkt_c in_pkt);*
> // code..
> vif.abort <= 1'b1;
> *expect ( @(posedge vif.clk) vif.mst_abort ##[5:8] vif.slv_resp ==
> ABORTED)*
> * continue2(); // pass action block*
> *else abort_error() ); // fail action block*
> *endtask : driver*
> endclass : mst_bfm
>
> In fact, this is how envisioned the application of the "expect" in a
> class.
> Ben
>
> On Tue, Jun 22, 2010 at 12:28 PM, Eduard Cerny <Eduard.Cerny@synopsys.com>wrote:
>
>> Hi Ben,
>>
>>
>>
>> did you say that the example uses an expect? I do not see one.
>>
>>
>>
>> Thanks,
>>
>> ed
>>
>>
>>
>>
>>
>> *From:* owner-sv-ac@eda.org [mailto:owner-sv-ac@eda.org] *On Behalf Of *ben
>> cohen
>> *Sent:* Tuesday, June 22, 2010 1:30 PM
>> *To:* Korchemny, Dmitry; sv-ac@eda.org
>> *Subject:* [sv-ac] Fwd: sv-ac: virtual interface application example
>>
>>
>>
>>
>>
>> ---------- Forwarded message ----------
>> From: *ben cohen* <hdlcohen@gmail.com>
>> Date: Tue, Jun 22, 2010 at 9:58 AM
>> Subject: sv-ac: virtual interface application example
>> To: sv-ac@eda.org
>>
>> * `define TOP fifo_tb*
>>
>> module fifo_tb;
>>
>> ...
>>
>> * fifo_if f_if(.*); // instantiation of fifo interface*
>>
>> endmodule : fifo_tb
>>
>>
>>
>> class Fifo_env extends vmm_env; // ENVIRONMENT
>>
>> ....
>>
>> Fifo_cmd_xactor fifo_cmd_xactor_0; // command-layer declaration
>>
>> ...
>>
>> endclass : Fifo_env
>>
>>
>>
>> function void Fifo_env::build();
>>
>> ...
>>
>> this.fifo_cmd_xactor_0 = new("cmd_xactor",
>>
>> 0,
>>
>> * `TOP.f_if,* // <----- actual interface passed
>>
>> fifo_channel_0,
>>
>> fifo_response_chan0
>>
>> );
>>
>> ...
>>
>>
>>
>> endfunction : build
>>
>>
>>
>> class Fifo_cmd_xactor extends vmm_xactor;
>>
>> *virtual fifo_if.fdrvr_if_mp f_if;*
>>
>> ...
>>
>> function new(...
>>
>> virtual fifo_if.fdrvr_if_mp new_vir_if,
>>
>> ... );
>>
>> *this.f_if = new_vir_if;*
>>
>> ...
>>
>> endfunction : new
>>
>> endclass: Fifo_cmd_xactor
>>
>>
>>
>> task Fifo_cmd_xactor::push_task (word_t data);
>>
>> * f_if.driver_cb.data_in <= data;*
>>
>> * f_if.driver_cb.push <= 1'b1;*
>>
>> * f_if.driver_cb.pop <= 1'b0;*
>>
>> * @ ( f_if.driver_cb);*
>>
>> * f_if.driver_cb.push <= 1'b0;*
>>
>> endtask : push_task
>>
>>
>>
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>
>
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