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Introduction
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In this chapter we shall see ports and signal types in details. |
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Accessing Ports/Signals
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In last chapter we saw how ports are declared and different types of ports. Here we will see how to access them. It is not a good idea to access ports directly, either for reading or writing. Port data types should use following methods to access them. |
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- port_name.write('value') : For writing value to port
- port_name.read() : For reading value from port
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write() and read() methods does the automatic type conversion from other data types to port data types. It is not always possible to use same data types of ports or signals inside processes. When using different data types, it is always good to use port_name.read() and port_name.write("value") to access the ports and same rule apply for signals. |
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Example : Accessing Ports/Signals
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1 #include <systemc.h>
2
3 SC_MODULE(ports_access) {
4 sc_in<sc_bit> a;
5 sc_in<sc_bit> b;
6 sc_in<bool> en;
7 sc_out<sc_lv<2> > out;
8
9 // Method to manipulate output
10 void body () {
11 // Ports should use read() method to read values
12 if (en.read() == 1) {
13 // Should use write() method of write values
14 out.write(a.read() + b.read());
15 }
16 }
17 // Method to monitor ports
18 void monitor () {
19 cout << "@" << sc_time_stamp() <<" a : " << a
20 << " b : " << b << " en : " << " out : "
21 << out.read() <<endl;
22 }
23
24 SC_CTOR(ports_access) {
25 SC_METHOD(body);
26 sensitive << a << b << en;
27 SC_METHOD(monitor);
28 sensitive << a << b << en << out;
29 }
30
31 };
32
33 // Testbench to generate test vectors
34 int sc_main (int argc, char* argv[]) {
35 sc_signal <sc_bit> a;
36 sc_signal <sc_bit> b;
37 sc_signal <bool> en;
38 sc_signal <sc_lv<2> > out;
39
40 ports_access prt_ac("PORT_ACCESS");
41 prt_ac.a(a);
42 prt_ac.b(b);
43 prt_ac.en(en);
44 prt_ac.out(out);
45
46 sc_start(0);
47 // Open VCD file
48 sc_trace_file *wf = sc_create_vcd_trace_file("ports_access");
49 sc_trace(wf, a, "a");
50 sc_trace(wf, b, "b");
51 sc_trace(wf, en, "en");
52 sc_trace(wf, out, "out");
53 // Start the testing here
54 sc_start(1);
55 a = sc_bit('0');
56 b = sc_bit('0');
57 en = 1;
58 sc_start(1);
59 a = sc_bit('1');
60 sc_start(1);
61 b = sc_bit('1');
62 sc_start(2);
63
64 sc_close_vcd_trace_file(wf);
65 return 0;// Terminate simulation
66 }
You could download file ports_access.cpp here
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Simulation Output: Accessing Ports/Signals
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SystemC 2.0.1 --- Oct 6 2006 19:17:37
Copyright (c) 1996-2002 by all Contributors
ALL RIGHTS RESERVED
@0 s a : 0 b : 0 en : out : XX
WARNING: Default time step is used for VCD tracing.
@1 ns a : 0 b : 0 en : out : XX
@1 ns a : 0 b : 0 en : out : 00
@2 ns a : 1 b : 0 en : out : 00
@2 ns a : 1 b : 0 en : out : 01
@3 ns a : 1 b : 1 en : out : 01
@3 ns a : 1 b : 1 en : out : 10
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Copyright © 1998-2014 |
Deepak Kumar Tala - All rights reserved |
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Do you have any Comment? mail me at:deepak@asic-world.com
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