Group EventGroup
Modules
| Type | Name |
|---|---|
| module | EventGroupHandle_t |
| module | xEventGroupClearBits |
| module | xEventGroupClearBitsFromISR |
| module | xEventGroupCreate |
| module | xEventGroupGetBits |
| module | xEventGroupGetBitsFromISR |
| module | xEventGroupSetBits |
| module | xEventGroupSetBitsFromISR |
| module | xEventGroupSync |
| module | xEventGroupWaitBits |
Detailed Description
An event group is a collection of bits to which an application can assign a meaning. For example, an application may create an event group to convey the status of various CAN bus related events in which bit 0 might mean "A CAN message has been received and is ready for processing", bit 1 might mean "The application has queued a message that is ready for sending onto the CAN network", and bit 2 might mean "It is time to send a SYNC message onto the CAN network" etc. A task can then test the bit values to see which events are active, and optionally enter the Blocked state to wait for a specified bit or a group of specified bits to be active. To continue the CAN bus example, a CAN controlling task can enter the Blocked state (and therefore not consume any processing time) until either bit 0, bit 1 or bit 2 are active, at which time the bit that was actually active would inform the task which action it had to take (process a received message, send a message, or send a SYNC).
The event groups implementation contains intelligence to avoid race conditions that would otherwise occur were an application to use a simple variable for the same purpose. This is particularly important with respect to when a bit within an event group is to be cleared, and when bits have to be set and then tested atomically - as is the case where event groups are used to create a synchronisation point between multiple tasks (a 'rendezvous').