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lab12 [2019/01/11 09:21]
dan.tudose [The Event Timer] 		lab12 [2019/01/11 09:27] (current)
dan.tudose [Processes]
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 This tutorial will show how to make use of timers in Contiki. It will also give a basic into to events. This tutorial will show how to make use of timers in Contiki. It will also give a basic into to events.
 +
 +===== Processes =====
 +
 +All Contiki programs are processes. A process is a piece of code that is executed regularly by the Contiki system. Processes in Contiki are typically started when the system boots, or when a module that contains a process is loaded into the system. Processes run when something happens, such as a timer firing or an external event occurring.
 +
 +Code in Contiki can run in one of two execution contexts: cooperative or preemptive. Code running in the cooperative execution context is run sequentially with respect to other code in the cooperative context. Cooperative code must run to completion before other cooperatively scheduled code can run. Preemptive code may stop the cooperative code at any time. When preemptive code stops the cooperative code, the cooperative code will not be resumed until the preemptive code has completed. The concept of Contiki's two scheduling contexts is illustrated above.
 +
 +Processes always run in the cooperative context. The preemptive context is used by interrupt handlers in device drivers and by real-time tasks that have been scheduled for a specific deadline. 
 +
 +An example process that receives events and prints out their number:
 +<code C>
 + #include "contiki.h"
 + 
 + PROCESS(example_process, "Example process");
 + AUTOSTART_PROCESSES(&example_process);
 + 
 + PROCESS_THREAD(example_process, ev, data)
 + {
 +   PROCESS_BEGIN();
 + 
 +   while(1) {
 +     PROCESS_WAIT_EVENT();
 +     printf("Got event number %d\n", ev);
 +   }
 + 
 +   PROCESS_END();
 + }
 +</code>
 +
 +The complete reference on Contiki processes can be found [[https://github.com/contiki-os/contiki/wiki/Processes|here]].
 +
 Contiki provides three kinds of timers: Contiki provides three kinds of timers:
   * **Simple timer:** The timer library provides functions for setting, resetting and restarting timers, and for checking if a timer has expired. An application must "manually" check if its timers have expired, meaning that this library does not post an event when the timer expires, so we must implement a routine that checks the timer for expiration.    * **Simple timer:** The timer library provides functions for setting, resetting and restarting timers, and for checking if a timer has expired. An application must "manually" check if its timers have expired, meaning that this library does not post an event when the timer expires, so we must implement a routine that checks the timer for expiration. 
lab12.1547191289.txt.gz · Last modified: 2019/01/11 09:21 by dan.tudose

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