RTOS Task Notifications
Used As Light Weight Mailbox
RTOS task notifications can be used to send data to a task, but in a much more
restricted way than can be achieved with an RTOS queue because:
Hence the phrase ‘lightweight mailbox’ is used in preference to ‘lightweight queue’.
The task’s notification value is the mailbox value.
Only 32-bit values can be sent
The value is saved as the receiving task’s notification value, and there
can only be one notification value at any one time
Data is sent to a task using the xTaskNotify() (or xTaskNotifyIndexed())
and xTaskNotifyFromISR() (or xTaskNotifyIndexedFromISR()) API
functions with their eAction parameter set to either eSetValueWithOverwrite or
eSetValueWithoutOverwrite. If eAction is set to eSetValueWithOverwrite then the
receiving task’s notification value is updated even if the receiving task already
had a notification pending. If eAction is set to eSetValueWithoutOverwrite then
the receiving task’s notification value is only updated if the receiving task
did not already have a notification pending – as to update the notification value
would overwrite the previous value before the receiving task had processed it.
A task can read its own notification value using xTaskNotifyWait()
See the documentation for the relevant API functions for examples.
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