ESP32 FreeRTOS: Connecting edp_http_client to UART with uart_echo Example

Question

Hi. I'm dabbling in ESP32 and starting to adopt FreeRTOS. My goal is to connect the edp_http_client examples to the UART. I am attaching the whole project below. For now, I've created a simple program based on uart_echo to see how to call several different processes (cutting out everything that...

khoam · Accepted Answer

. In the FreeRTOS documentation it states: Tasks are normally implemented as an infinite loop, and must never attempt to return or exit from their implementing function. Your my_task () function should therefore look like this, for example: Code: C / C++Log in, to see the code . Source .

Anonymous · Accepted Answer

Task, despite being a normal function from the C point of view, has no right to return via return from a function. If it is not needed, it should be removed using the appropriate function. The system will release its context etc. Such a function is vTaskDelete. Of course you have to set INCLUDE_vTaskDelete to 1 in the configuration file.

In addition, if you delete a task, you must remember that the idle task gets the CPU time, because the deletion takes place right there.

Additionally, the task itself cannot return via return.

If you want a task to execute only once and then delete itself

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.

Of course there are many other ways than while(1) vTaskDelay(1); I deliberately don't write about them at the moment because they either require a longer explanation or the right configuration

khoam · Accepted Answer

. Simply via vTaskSuspend() : More elegantly by using xTaskNotifyGive() and ulTaskNotifyTake(), but this is a bit more difficult: . I don't want to answer that question, because there are as many rules in the Forum as there are participants

dondu · Answer

After your comments, I added a delete shuffle and added a second task. Both increase the global variable while I moved the loop to the app_main() function: Code: C / C++Log in, to see the code . The result is: . Why is it that although the variable length is global the results are every 2?

khoam · Answer

Below is the solution to the problem, and now read about semaphores and accessing global variables from FreeRTOS tasks . Code: C / C++Log in, to see the code .

Anonymous · Answer

I see you are trying to invent your own RTOS

governed by its own laws. (For those who understand otherwise, this is a joke).

1 I don't know what app_main , but if it's something you prefer from main after schedular starts - it's wrong. After schedular starts in min there should be nothing because this code should not execute.

2. in the still shuffle they can exit via return. This cannot be the case.

3) If multiple threads refer to the same object then you need to ensure some synchronisation. In this case you must ensure that only one thread has exclusive access to the variable.

4. if you assume that the function that starts the shuffle is another shuffle, and you only want 2 of them to start, then you also need to synchronise this. Because you may find that you are starting many more shuffles than they are deleting.

Nobody does it that way anyway. Note that even just deleting the shuffle is optional in freeRTOS - many applications never do this.

In addition, deleting tapes does not release the memory used by the task. This has to be done "manually" (if the task has allocated something dynamically, of course).

khoam · Answer

. Another I don't know, but I'll comment style statement. Please refer to the ESP-IDF documentation, where it is described how the app_main is constructed. . This can be the case and is correct. The task is deleted. Please take a look at the example from the FreeRTOS documentation: . Please keep these kinds of puppyish remarks to the participants Added after 1 [hour] 14 [minutes]: . And if it does not allocate (as in the case of the code shown in post #4) then this (releasing memory) is done automatically during the Idle task. Added after 1 [minute]: . That is, you may or may not do this depending on what you want to do e.g. in the case of ESP32 such a restart is required to reassign a task to another core. Added after 50 : . This is why the mutex was used in the code in post #5 - xSemaphoreCreateMutex(). Added after 1 [hour] 9 [minutes]: .An alternative way to use a mutex in this case is to use the atomic type atomic_int : Code: C / C++Log in, to see the code .

dondu · Answer

Is everything OK now? Code: C / C++Log in, to see the code . The result is correct because my_task runs every second and my_task_2 runs every 5 seconds: Code: HTML, XMLLog in, to see the code .

khoam · Answer

. So the code should also be correct . You have changed the strategy: you no longer create shuffles in app_main every time, i.e. in the normal way . In the function assigned to tasks, vTaskDelete(NULL) is redundant at the moment, unless you exit the while(1) loop with e.g. some break.

dondu · Answer

. I meant whether it complies with FreeRTOS rules . Yes, yes, I read the link you pointed to vTaskDelete(). If I needed one task to pause the other for a while, what would need to be done?

Anonymous · Answer

You can, for example, send a task to vTaskSuspend

Anonymous · Answer

this won't work because the task you want to stop has to block itself while waiting for the notification.

dondu · Answer

I reworked app_main() adding a handle when creating my_task_2 and in my_task I added pausing my_task_2 and restarting it.

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.

Result correct:

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.

The next step is to integrate the UARTU and WiFi client.

khoam · Answer

. That's why I wrote about using ulTaskNotifyTake() - please quote in full and read with understanding. Added after 2 [minutes]: . It is OK.

Anonymous · Answer

. Full quote. Tell me how you stop another task elegantly with notification? If you find such a magic way then so can a semaphore or queue I understand perfectly but due to the rules I won't comment on it. To @dondu just suspend. Any other method requires the task to lock itself. Another task can only unblock it

khoam · Answer

. I won't directly stop another task with a notification, but I can cause the target task, upon receiving such a notification, to pause itself for a period of time specified in the notification sent - this is what the Author of the thread asked about in post #10. Added after 23 [minutes]: . I think it won't be long before the Author of the thread himself starts using notifications to determine the shuffle stop time, as soon as he faces the fact that the xTaskAbortDelay() function is not implemented in the FreeRTOS version for ESP32.

Anonymous · Answer

probably not about that though . LOL. I think dondu is a better programmer and won't face this problem.

khoam · Answer

. Exactly what it is about, but the way of interpretation remains divergent and let it stay that way.

dondu · Answer

Thanks to your help, currently:
- one task receives data from UART1 while showing what it has received on the same UART,
- a second task sends data to the database via http request using the POST method, showing one by one what it does in the monitor,
- the third test increments the variable by 1 and shows its value also in the monitor.
I deactivate the other two tasks for the duration of the http request service.

Now I need to add timekeeping. With FreeRTOS, can xTaskGetTickCount() be used for this task, or something else?

PS. I have changed the topic title as it no longer corresponds to its content

.

khoam · Answer

. I use the soft timers from FreeRTOS for this task: Added after 2 [minutes]: .In the ESP-IDF itself you also have timers, of course, if you want more precise timing.

Anonymous · Answer

Yes it can.

dondu · Answer

Yes, of course I know there are timers in ESP32, but for now I'm concentrating on getting to know FreeRTOS hence the reason I'm asking about it.
I'm currently using xTaskGetTickCount(), but will familiarise myself with what you've provided.

Anonymous · Answer

But I still don't understand how to elegantly do it. The task you want to put to sleep has to poll all the time to see if there is a notification to go into a locked state- which is definitely not elegant nor in the spirit of multitasking. So bring me closer to this elegance. In addition suspended != blocked. . Also a circular method because the freeRTOS timers are used to call a callback after a certain time has elapsed. This callback in turn must notify the task. In addition, the software timers are based on the queues in freeRTOS - and these are resource intensive. So software timers are useful, but I don't know if that's what Kol dondu meant - because for timeouts, for example, they are completely unsuitable.

dondu · Answer

For the time being, I want to count down time intervals of about 15 minutes. This is needed because every such time the data is to be sent to the database. I wrote approximately because the tolerance can be as short as ±1 minute.

khoam · Answer

. The soft timer does not need to notify task. Only the timer handler is passed in the callback, and the action it further calls does not have to be related to the FreeRTOS task. Added after 1 [minute]: . . It all depends on what you want to happen after this countdown of the set time. If you want to send some data to the database, the callback in the soft timer will be appropriate.

Anonymous · Answer

If it is only to wait and so to speak it is not to unlock vTaskDelay( xDelay );

khoam · Answer

. The callback in the soft timer can also unblock the task by sending an appropriate notification.

dondu · Answer

Around the clock measurements are taken and averaged, and sent to the base every 15 minutes. I will also use Software Timers to get to know them .

Anonymous · Answer

get to know the queues better. Task sending locks onto a data queue. Task collecting data as time elapses adds to this queue which unlocks the sending task, which after sending again locks on accessing the queue

ESP32 FreeRTOS: Connecting edp_http_client to UART with uart_echo Example

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