NRF SDK Scheduler vs. Task Manager

[jtrovato]

Hello,

I am trying to setup my project's architecture and I am trying to take advantage of some of the awesome libraries in the SDK. I am a bit confused on the differences between the Task Manager and the Scheduler and what each is best suited for.

From reading the SDK 16/17 docs, it seems like the Scheduler is basically an event queue that takes execution out of low level context and into main context. Seems pretty useful for freeing up the BLE stack or other modules while servicing interrupts, but what is a situation in which this would benefit me over the normal event handling structure? Maybe if multiple interrupts are coming in at the same time those low level modules reject the second if currently servicing the first?

Next there is the Task Manger which is basically a cooperative scheduler. This seems like it is useful if you have multiple contexts that you want to run code from simultaneously. It also has the ability to wait for events or yield to the next task, which seems useful. This seems like I would need to have more than just event servicing routines in my project to make task switching useful. what situation would this be useful in? 

Both of these libraries are fancy ways to execute callbacks so what is the difference if I use Task Manager and task_events_set() in ISRs and service in specific task vs using the Scheduler and calling app_sched_event_put() from the ISR? 

Finally I am trying to structure my application such that it is as event driven as possible. That means that most of my code will be executed in response to HW or BLE interrupt/events. If this is truly the case then it seems like I would just need the scheduler to offload my peripherals,  but I noticed that the template example comes standard with the Task Manager and implements and idle task. My specific questions:

1. Can you use the Task Manager and Scheduler in tandem? Is there a use case or benefit?
2. What benefits does the Task Manager provide to architecture? Do I need to have more than just events and an idle task for the task manager to be worth keeping as the default architecture?
3. How is the idle task better than just having your main loop call everything in the idle task?
4. What is the ideal use case for the Task manager?

Thanks in advance!

[Simonr]

Hi

1. I assume you're referring to the Experimental: Task manager, and the Schedule handling library? As of writing this, I can't think of a use case where you would benefit from using both of these, as I think one or the other should be more than sufficient.

2. First off, the Task manager is still an experimental library, which indicates that it is not properly tested from our side, and may not have the same quality as you can expect from the other SDK modules. So for a thoroughly tested module, I would suggest going for the Scheduler over the Task Manager. However, if you'd like the more advanced features like the dynamic task creation, synchronization options, etc. you should go with the Task Manager.

3. The idle task ensures that you won't have to leave the task context in order to run these functions, and would be the equivalent to the main loop inside the task context.

4. Please check out the Console over Bluetooth Application which is the only example we have that runs the task manager. Here you can see how it is used to start the task manager after all initialization is done, and run the application from there. 

Please note that we're entering the summer vacation period here in Norway, so delays must be expected as we are low on staff for the month of July. Sorry about the inconvenience!

Best regards,

Simon