SystemC 22 Signal - Many Writers
Class definition of sc_signal
1
2
3
template <class T,
sc_writer_policy WRITER_POLICY = SC_ONE_WRITER>
class sc_signal: public sc_signal_inout_if<T>, public sc_prim_channel {}
- If
WRITER_POLICY == SC_ONE_WRITER,- it shall be an error to write to a given signal instance from more than one process instance at any time during simulation.
- If
WRITER_POLICY == SC_MANY_WRITERS:- a) it shall be an error to write to a given signal instance from more than one process instance during any given evaluation phase,
- b) but different process instances may write to a given signal instance during different delta cycles.
Thus, by default an sc_signal has only one writer; when declared as MANY_WRITERS, the writers can write to the signal channel at different time.
As to consumers, an sc_signal may have more than one consumers. They can all read from the signal channel at same or different time.
Code
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
// Learn with Examples, 2020, MIT license
#include <systemc>
using namespace sc_core;
SC_MODULE(MULTI) {
sc_signal<int> s1; // a single-writer signal
sc_signal<int, SC_MANY_WRITERS> s2; // a multi-writer signal
SC_CTOR(MULTI) {
SC_THREAD(writer1); // writes to s1
SC_THREAD(writer2); // writes to s1 and s2
SC_THREAD(consumer1);
sensitive << s1; // sensitive to s1
dont_initialize();
SC_THREAD(consumer2);
sensitive << s1 << s2; // sensitive to s1 and s2
dont_initialize();
}
void writer1() {
int v = 1; // init value
while (true) {
s1.write(v); // write to s1
s2.write(v); // write to s2
std::cout << sc_time_stamp() << ": writer1 writes " << v++ << std::endl;
wait(1, SC_SEC); // write every 1 s
}
}
void writer2() {
int v = -1; // init value
while (true) {
// s1.write(v); /* cannot, otherwise runtime error: (E115) sc_signal<T> cannot have more than one driver*/
wait(SC_ZERO_TIME); // needed to offset the write time. Otherwise runtime error: conflicting write in delta cycle 0
s2.write(v); // write to s2
std::cout << sc_time_stamp() << ": writer2 writes " << v-- << std::endl;
wait(1, SC_SEC); // write every 1 s
}
}
void consumer1() {
while (true) {
std::cout << sc_time_stamp() << ": consumer1 reads s1=" << s1.read() << "; s2=" << s2.read() << std::endl; // read s1 and s2
wait(); // wait for s1
}
}
void consumer2() {
while (true) {
std::cout << sc_time_stamp() << ": consumer2 reads s1=" << s1.read() << "; s2=" << s2.read() << std::endl; // read s1 and s2
wait(); // wait for s1 or s2
}
}
};
int sc_main(int, char*[]) {
MULTI consumers("consumers");
sc_start(2, SC_SEC); // run simulation for 2 s
return 0;
}
// Result:
// what happens at time 0 s:
// writer1 update value for s1 and s2
0 s: writer1 writes 1
// consumer2 triggered on s1, s2
0 s: consumer2 reads s1=1; s2=1
// consumer1 triggered on s1
0 s: consumer1 reads s1=1; s2=1
// writer2 update value again after delta cycle
0 s: writer2 writes -1
// consumer2 triggered on s2
0 s: consumer2 reads s1=1; s2=-1
// what happens at time 1 s:
1 s: writer1 writes 2
1 s: consumer2 reads s1=2; s2=2
1 s: consumer1 reads s1=2; s2=2
1 s: writer2 writes -2
1 s: consumer2 reads s1=2; s2=-2