How to get/use the written/read event of sc_fifo?

[yatung]

Hello Everyone,

I am a beginner at systemc.

I am interested in sc_fifo channel and investigated the OSCI simulator source code.

I found sc_fifo has a member function named "data_written_event" and its prototype is like below:

virtual const sc_event& data_written_event() const;

I want to get a callback/notify when a specific sc_fifo channel is written or read. My solution is:

- Preface

I used the sc_get_top_level_objects() and get_child_objects() to iterate out all the sc_object.

(This is the way I get the sc_fifo object)

- Make a callback/sensitive by user code

1. Try to get the written/read event data member of sc_fifo

2. Use the add_static() member function of sc_event to register a written/read event callback

for this sc_fifo

Is the solution above workable?

----------------------------------------------

- My Test Result

1. Try to get the written/read event data member of sc_fifo

==> Because of the "operator=" is overwritten as private:

sc_fifo& operator = ( const sc_fifo<T>& );

I canNOT get the event in user code.

ex: sc_event e; e = sc_fifo_obj->data_written_event(); //<-- Error! Of course.

2. add_static() is s private member function of sc_event class and I can neither use it in

user code.

Can you experts guide me how to do it or give me any hint?

Appreciate your feedback.

by yaTung

[Philipp A Hartmann]

I am interested in sc_fifo channel and investigated the OSCI simulator source code.

First of all, you should refer to the standardized API in the IEEE Std. 1666-2011, instead of looking at the source code of the proof-of-concept implementation. This way you make sure that your solution works in other standards-compliant implementations as well.

I want to get a callback/notify when a specific sc_fifo channel is written or read. My solution is:

- Preface

I used the sc_get_top_level_objects() and get_child_objects() to iterate out all the sc_object.

(This is the way I get the sc_fifo object)

I assume there are specific reasons, why you can't use a proper sc_port (e.g. sc_fifo_in/out), connected to the particular sc_fifo instance of interest? Looping through the design hierarchy to manipulate the model structure is a rather special case in SystemC.

- Make a callback/sensitive by user code

1. Try to get the written/read event data member of sc_fifo

2. Use the add_static() member function of sc_event to register a written/read event callback

for this sc_fifo

Is the solution above workable?

No. As you have seen in your tests, the add_static function is private and non-standard. It is an implementation artefact. Instead, you should spawn a process, which is then sensitive to the events. Processes are the natural way to specify event-triggered functionality in SystemC.

1. Try to get the written/read event data member of sc_fifo

==> Because of the "operator=" is overwritten as private:

sc_fifo& operator = ( const sc_fifo<T>& );

I canNOT get the event in user code.

ex: sc_event e; e = sc_fifo_obj->data_written_event(); //<-- Error! Of course.

If you need to keep a handle to an event, you can use a C++ reference (or pointer), instead of creating a new event instance. Events have "identity" and can not be copied or assigned. This is the case for many structural elements in SystemC.

sc_event const & ev_ref = sc_fifo_obj->data_written_event();

In the easiest case, you can just create a plain SC_METHOD process, being sensitive to your event. Of course, this requires to wrap the "callback" in a module instance. To make sure your FIFO has been created already, you should create this process in the end_of_elaboration callback of the module:

SC_MODULE( fifo_callback_handler )
{
 // ...
 void callback_process();
 void end_of_elaboration()
 {
// ... find fifo object
SC_METHOD(callback_process);
  sensitive << sc_fifo_obj->data_written_event();
  dont_initialize(); // do not run at start of simulation
 }
};

You can also use dynamic processes (sc_spawn, sc_bind) to create processes dynamically during the simulation. See 1666-2011, Section 5.5.

Greetings from Oldenburg,

Philipp