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pmatheusvinhas

Getting a bit from bus

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Hey.

It's my first time with SystemC and I'm having the following problem:

I made a control matrix that generates a 12 bits control word (sc_bv<12> CON) and I'm trying to get the 10th bit of that word. On my top level cpp I did the following:

sc_signal<sc_bit<12> > bus_CON;

sc_bv<12> var_bus_CON;

var_bus_CON = bus_CON;

sc_signal<bool> busCON10;

busCON10 = var_bus_CON[10];

and after I'm connecting the ref. variable that I want with that previous signal:

programcounter.Ep( busCON10 );

And It's not working. My signal gives me hi impedance at all simulation time. A case that should happen when Ep = 0.

p.s: matrix.CON( bus_CON );

Did I make anything wrong?

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First thing you need to realize is that sc_signal<> is not a wire and it is not a data type. sc_signal<> is a channel with a non-blocking write and a blocking read. You cannot "connect" a variable to a signal. You have to explicitly make the transfer each time the value changes. There is no equivalent to a Verilog continuous assignment.

How do you know if a signal has changed? You have to explicitly watch/wait for the change using additional methods value_changed_event() or possibly posedge_event() if using sc_signal<bool> or sc_signal<sc_logic>.

Due to overloading of operator=(), the innocuous looking busCON10 = var_bus_CON[10] turns into:

busCON10.write(var_bus_CON[10].read()); which will not return a value until the end of the next delta cycle. Using a cout << busCON directly after this will yield the current delta's value.

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