RTX166 Tiny User's Guide

Events

Events in a real-time operating system may be used to control the execution of tasks in the program. A task may wait for an event or may set event flags for other tasks.

The os_wait function allows a task to wait for one or more events.

• The Timeout is a common event for which a task can wait. A timeout is simply a number of clock ticks. While a task waits for a timeout, other tasks may execute. Once the specified number of timer ticks elapses, the task may continue execution.
• The Interval is a variation of the Timeout. An interval is like a timeout except that the specified number of clock ticks is relative to the last time the os_wait function was invoked by the task. The Interval may be used to generate a task which is run on a regular, synchronous schedule (like once every second) regardless of how long the task takes between calls to os_wait. If the specified number of clock ticks have already elapsed (since the os_wait function was last invoked) the task is re-started immediately—no other tasks execute.
• A Signal is a simple form of inter-task communication. A task can wait for another task to send it a signal (with the os_send_signal and isr_send_signal functions).

Each event has an associated event flag that RTX166 Tiny maintains. The following event selectors may be used with the os_wait function to specify what to wait for:

When the os_wait function returns, the events that occurred are specified by the return value:

The os_wait function may wait for the following combinations of events:

• K_SIG | K_TMO: os_wait delays the task until a signal is sent to it or until the specified number of clock ticks has elapsed.
• K_SIG | K_IVL: os_wait delays the task until a signal is sent to it or until the specified interval has elapsed.

Note

• The K_IVL and K_TMO event selectors may not be combined.