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Bind failure when passing an sc_fifo_in port through 2 hierarchies to a dymanic process


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Apologies for the poorly worded Title...

I am experiencing an odd (to me) issue when constructing a model in which I have a hierarchy more than 1 level deep. ie: I have an sc_module instantiated within another sc_module, and I am attempting to bind an sc_fifo_in (also an out, but I've simplified to a single port for a testcase) from a testbench through the first sc_module to a second. The lowest-level module within the hierarchy has no static process defined by the constructor but instead spawns dynamic processes only which process the fifo.

I can make this code work by either:

  • defining a static process and not using the dynamic process (not ideal for my actual application as I have multiple of these to spawn)
  • only have a single level of hierarchy such that I'm not passing the sc_fifo_in port through an sc_module to the second

I created 3 examples on EDA Playground rather than posting 70+ lines of code here. If anyone prefers to see the code here instead, I'm happy to paste it.

Here is the first example which works (only a single hierarchy level and using a dynamic process only): Working example

Here is a second example which works (two levels of hierarchy and uses a static process only): Working example

Here is the second example which fails (two levels of hierarchy and uses a dynamic process only): Failing example

I have been trying to determine what I am doing wrong all day, and I have drastically simplified my actual code down to this very simple (not terribly interesting) example. In the Failing case, SystemC reports error E112 - port is not bound (I am building with SystemC 2.3.4).

I assumed that there was an issue with not having a static process in my BottomHier module and only having a dynamic process, but when I remove the TopHier level as in my first Working Example above, the code compiles and binds ok. And the second example demonstrates that I can successfully pass an sc_fifo_in port through 2 sc_modules without issue. 

Is there some limitation I am experiencing when attempting to pass the sc_fifo_in through the TopHier module and binding it to the BottomHier module related to the use of a dynamic process? I simply want TopHier to be a pass-through in this example.

I appreciate any advice here.

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The root cause of the problem is the following: in your constructor your are trying to call a function of the sc_fifo_in_if which is not yet bound when having a hierarchical binding.

Why is then example 2 woring? There is a difference in your example 2 (working with static process) and 3 (non-working): you use a thread in example 2 and a methoid in example 3. To react on the event in example 3 you need to access the interface during construction (where it is not being bound) while in example 2 the thread accesses the port during simulation (where the port is bound.

I see 3 options:

  • use sc_fifo_in::data_written() which returns an sc_event_finder instead of an event (this would be the correct way)
  • use a dynamic thread instead of a dynamic method
  • spawn your method in the end_of_elaboration() call, port are then bound
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Thank you very much not only for the quick reply but also the great information. I do have a followup question.

You state that I use a method in example 3 vs. a thread in example 2. In my spawn options I did not define the process as a method. And given that the read() function is a blocking function, I believe that the process_fifo_in process is actually a thread. Can you please clarify if I am incorrect?

Regardless of that, I was able to make both suggestion 1 and and suggestion 3 work.

Is there a preference for spawning the processes in before_end_of_elaboration vs. end_of_elaboration?

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Actually you are right, sc_spawn_options default is SC_THREAD.

For spawning there is no preference or even difference. But for your ports there is a difference: only in end_of_elaboration ports are completely bound and you can access the events of the associated channel. If you do this in before_end_of_elaboration() you will run into the same problems you had initially Pls. check also the LRM wrt this.

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