Since it is possible to send data with different QoS using a single bulk endpoint, you might want to prioritize the transfers by their QoS latency (medium latency transfers processed before high latency transfers, for instance). This kind of prioritization is implemented inside PHDC µC/OS-II and µC/OS-III RTOS layer. Table - QoS Based Scheduler Priority Values shows the priority value associated with each QoS latency (the lowest priority value will be treated first).
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If no QoS based priority management is implemented, the OS will then resume the tasks in the order of their OS priority. In this example, the task that has the higher OS priority, A, will be resumed first. However, that task wants to write data that can have very high latency (QoS priority of 3). A better choice would be to resume task B first, which wants to send data that can have medium latency (QoS priority of 1). Figure - Task Execution Order, Without QoS Based Scheduling and Figure - Task Execution Order, with QoS Based Scheduling represent this example without and with a QoS-based scheduler, respectively.
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