This chapter focuses on how tasks can synchronize their activities with Interrupt Service Routines (ISRs), or other tasks.
When an ISR executes, it can signal a task telling the task that an event of interest has occurred. After signaling the task, the ISR exits and, depending on the signaled task priority, the scheduler is run. The signaled task may then service the interrupting device, or otherwise react to the event. Servicing interrupting devices from task level is preferred whenever possible, since it reduces the amount of time that interrupts are disabled and the code is easier to debug.
There are two basic mechanisms for synchronizations in µC/OS-III: semaphores and event flags.