EECE 276 – Embedded Systems1EECE 276Embedded SystemsTask communication:Queues, mailboxes, pipesEECE 276 – Embedded Systems2Task communicationO Tasks need to communicate:O Shared data structure: QueueO Operations: (RTOS services)» Queue Initialize(int size): create and set up for size» Void Enqueue(Queue q,void* item): block if full, else put» Void* Dequeue(Queue q): block if empty, else getO Multiple tasks use it: mutual exclusion is enforcedProducerTaskConsumerTaskEECE 276 – Embedded Systems3Task communicationO Mailboxes: » Similar to queues, (usually) has a single element and two states: empty/full» If multiple tasks are waiting for a mailbox, the highest priority one gets the messageO Pipes:» Streams of data » Typically use fwrite()/fread() operations» Arbitrary length and data formatEECE 276 – Embedded Systems4Using queuesProducerTaskConsumerTaskQueue1-to-1:ProducerTaskConsumerTaskQueue1-to-many:ConsumerTaskHighest priority task gets the dataEECE 276 – Embedded Systems5Using queues, mailboxesProducerTaskConsumerTaskQueueMany-to-1:ProducerTask(Non-deterministic) Merge of dataMBox1MBox2ConsumerTaskProducerTaskDouble buffer:EECE 276 – Embedded Systems6Problems with queues, etc.O If of finite size, task may block/receive error if full/emptyO Passing pointers as queue elements: data becomes shared (“ownership” changes)O The sender and the receive must agree on the format/meaning of the data passed » void* is not a very good ideaO Memory management: running out of memory space leads to disasters (or
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