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program example();
// semaphores are a unique datatype in SV semaphore want_to_print;
// this is the "shared resource", would be a bus,
// but in this case its a $display
task write_bus(int addr, int data);
$display("here is a write to the bus at addr %d", addr);
#100;
endtask
int done = 0, i = 0;
initial
begin
// here we initialize the semaphore with one token
// available to share. We could initialize
// with more, if there were an interleaved bus, for example
want_to_print = new(1);
fork
begin
// here is one parallel thread competing
while(1)
begin
// wait for some random time
#($random() % 100);
// attempt to get the one semaphore token want_to_print.get(1);
// got it!, lets use the bus
write_bus(200, $random());
i++;
// we must return the semaphore token want_to_print.put(1);
end
// here is a second parallel thread
begin
while(1)
begin
// wait for some random time
#($random() % 100);
// attempt to get the one semaphore token
//want_to_print.get(1);
// got it!, lets use the bus to the exclusion of others
write_bus(100, $random());
i++;
// we must return the semaphore token
want_to_print.put(1);
end
end
join_none
// this is main thread, running in parallel with the 2 others in
// the fork join_none.
while(i < 100)
begin
@(i);
end
// ok , now lets terminate the other 2 threads!
disable fork;
$display ("done -- out\n");
end
endprogram |
