How to send queue message to multipule receiver in freeRTOS?

Question

I'm looking for a method to broadcast a message using queue in freeRTOS and i come up with different ideas but each one has a different problem.

what i have:

• the item type for the queue is a struct with an attribute to indicate if the message is a broadcast or for a specific task.
• a broadcast task that will write a message to the queue.
• a queue manager task that will peek on the queue if any new message was received and if the message has a destination then it will resume that specific task or resume all tasks if it's an broadcast.

• and for the Receiver task i come up with those ideas:

  1. if i used the receive function xQueueReceive only the first task in task-queue will read the message and remove it from queue and with this, the other tasks will not be able to read that broadcast message. in the other hand, it's the perfect why for directed message (message for a specific task).
  2. if i use the peedk function xQueuePeek the message will never be removed from queue unless i use xQueueReceive which is kinda redundant (peek and receive in the same task, meeh, ugly coding) and i can't use any other delete function because it will remove the whole queue. but that will solve the message for a specific task, and to solve the broadcast message i need to set a priority for each receive task and only the task with the lowest priority will use xQueueReceive to remove that message from queue and all receive tasks will suspend themselves after peeking or reading so they don't read again the message (i'm not sure what to do about the queue manager task because i can't suspend it and it will keep notified about a new message in queue until the last task receive it), but the whole system will need to wait for that low priority task to run to remove that message and any new message received in that time, it will not be read in the real time.

i'm still thinking about other methods like using new queue or a queue for each receive task but i'm not sure yet which method is the best one. and i don't know if there any other why to broadcast a message even without using the queue technique.

i need to tell you that this program is not for a specific project. i'm just trying to use the Queue technique in different ways. and i already found other post about broadcasting a message but it was for a specific problem where they solve it without using the queue technique. i just want to send "this is a broadcast message" to the queue and all receiver be able to read it once (just one time).

thank you.

Answer 1

Event groups are the only broadcast mechanism in FreeRTOS. You could use an event group to unblock all tasks that should read from a queue using the queue peek function, then xEventGroupSync() to know when all tasks had read the data so the data should them be removed.