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program example();
// semaphores are a unique
datatype
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);
$display("here is a write to the
bus at addr %d", addr);
#100;
endtask
int done = 0, i = 0;
initial
begin
// here we initialize the
semaphore with one token
// availabe to share. We
could initialize
// with more, if there were
an interleaved bus, for
// example
want_to_print = new(1);
fork
begin
/// here is one
parallel thread competing
while(!done)
begin
// wait for some random time
#($random() % 100);
//
attempt to get the one semaphore token
want_to_print.get(1);
//
got it!, lets use the bus
write_bus(200, $random());
i++;
//
we must return the semaphore token
want_to_print.put(1);
end
end
// here is a second
parallel thread
begin
while(!done)
begin
// wait for
some random time
#($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
// here is a third
(Watchdog) parallel thread
// this is to decide when
we are done
begin
while(!done)
begin
@(i);
if
(i > 100)
done = 1;
end
end
join
$display ("done -- out\n");
end
endprogram |
