Arduino Protothreads by Example

Question

I am trying to get Arduino working with Protothreads and wanted to confirm I have the basic setup correct. If I have understood the API correctly, then the following code should be what I need to start 2 concurrent threads from inside an Arduino program:

#include <pt.h>
static struct pt t1, t2;
void setup() {
 PT_INIT(&t1);
 PT_INIT(&t2);
}
void loop() {
 doSomething(&t1, 500);
 doSomethingElse(&t2, 500);
}
static int doSomething(struct pt *pt, int interval) {
 PT_BEGIN(pt);
 sleep(100);
 PT_END(pt);
}
static int doSomethingElse(struct pt *pt, int interval) {
 PT_BEGIN(pt);
 sleep(250);
 PT_END(pt);
}

Does anyone see anything that jumps out at them as missing or wrong?

• Majenko: What is sleep() ?

Answer 1

Check this example: rather than sleep(), it uses PT_WAIT_UNTIL

 while(1) {
 PT_WAIT_UNTIL(pt, millis() - timestamp > interval );
 timestamp = millis();
 doSomething();
 }

That should be the proto-thread way of waiting: PT_WAIT_UNTIL will make sure that your thread sleeps in a way that allows other threads to run.

The rest looks fine, but I have not tried to run the code.

• Zhe Hu: Just to add to the understanding (or confusion), PT_WAIT_UNTIL blocks the execution or "yield" to the other threads. You can see its difference from sleep which blocks everyone. The while(1) "re-arms" the thread again, once dosomething() finishes. Here is some C switch-while hackery going on. (see dunkels.com/adam/pt/expansion.html)

Answer 2

Why reinvent the wheel? There are libraries that can do just that for you. For example ArduinoThread . I tried it out and did not need to keep looking further. There are also Wiring and SoftTimer but I did not try those.