 RTX51 Tiny User's Guide | |
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RTX51 Tiny User's Guide
Overview Real-Time Programs Theory of Operation
Timer Tick Interrupt Tasks Task Management Events Task Scheduler Round-Robin Task Switching Cooperative Task Switching Idle Task Stack Management Configuring RTX51 Tiny Using RTX51 Tiny Examples Function ReferenceEvents
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 the os_wait function. 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 task has a Ready flag which may be set by other tasks (with the os_set_ready and isr_set_ready functions). A task that is waiting for a timeout, interval, or signal may be started by setting its ready flag.
Each event has an associated event flag that RTX51 Tiny maintains. The following event selectors may be used with the os_wait function to specify what to wait for:
| Event Selector | Description |
|---|---|
| K_IVL | Wait for the specified interval. |
| K_SIG | Wait for a signal. |
| K_TMO | Wait for a specified timeout. |
When the os_wait functio returns, the events that occurred are specified by the return value:
| Return Value | Description |
|---|---|
| RDY_EVENT | The task's ready flag was set. |
| SIG_EVENT | A signal was received. |
| TMO_EVENT | A time-out has completed or an interval has elapsed. |
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.
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