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OSMemCreate() can only be called from task-level code, but OSMemGet() and OSMemPut() can be called by Interrupt Service Routines (ISRs).
Listing 17-4 shows an example of how to use the dynamic memory allocation feature of µC/OS-III, as well as message-passing capabilities (see Chapter 15, “Message Passing”Returning a Memory Block to a Partition). In this example, the task on the left reads and checks the value of analog inputs (pressures, temperatures, and voltage) and sends a message to the second task if any of the analog inputs exceed a threshold. The message sent contains information about which channel had the error, an error code, an indication of the severity of the error, and other information.
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Sometimes it is useful to have a task wait for a memory block in case a partition runs out of blocks. µC/OS-III does not support pending on partitions, but it is possible to support this requirement by adding a counting semaphore (see Chapter 13, “Resource Management” Resource Management) to guard the memory partition. The initial value of the counting semaphore would be set to the number of blocks in the partition. This is illustrated in Figure 17-5.
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