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Find file Copy path. Cannot retrieve contributors at this time. Raw Blame History. Start by reading the FAQ page "My application does not run, what could be wrong? Rest of task code. The first block is used to hold the queue's data structures.
Therefore xQueue1 is now a handle to a valid queue. The item is queued by copy, not by reference. Output the character now. Otherwise NULL is returned. You signed in with another tab or window. Reload to refresh your session. You signed out in another tab or window. All rights reserved. Full license text is available on the following. Start by reading. Have you.
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For example, a call to xQueueCreate. For example, a call to. This allocates the storage required by the. Each item on the queue must be. If the queue cannot be created then 0 is. If a queue is.09 FreeRTOS Tutorial: Queues part1
If a queue is created using.For most of the functionalities that we are going to use in this tutorial, you can check the. We will start our setup function by opening a serial connection, in order to be able to get the output of our testing program.
This will be our regular Arduino function. The arguments to this function are the following :. TaskCode : In this argument, we need to pass a pointer to the function that will implement the task. We will create two functions, TaskOne and TaskTwowhich we will define latter and will be passed in this argument.
TaskName : The name of the task, in a string. StackDepth : The size of the stack of the task, specified as the number bytes. There is no simple way of determining the size of the task , although some calculations can be made.
In this simple example, we will pass a value that is big enough. Parameter : Pointer to a parameter that the task function can receive. In this case, for simplicity of the code, we will not use it, so we pass NULL in the argument. Priority: Priority of the task. We will create both tasks with the same priority. TaskHandle: Returns an handle that can be used for latter reference of the task on calls to functions for example, to delete a task or change its priority .
Also, for this simple example, we are not going to use it, so it will be NULL. For now, we will assume that the tasks will be created without any problem, so we are not going to do any error checking. Naturally, for a real case scenario application, we would need to do that to confirm the tasks were created. So, check bellow the full setup function, already with the calls create the two different tasks.
Now, we only need to specify the functions for the tasks. Remember that we want to create a task implemented by function TaskOne and other implemented by function TaskTwo.
Note that task are implemented with regular functions and they only need to follow a predefined function prototype . Check an example bellow. A very important thing to take in consideration is that this function should not return. So, they must not contain a return statement or execute until the end of the code . Instead, they should be explicitly deleted . This function receives as input the handle of the task to be deleted  remember the previously mentioned argument of the xTaskCreate that we are not going to use.
Other that these particularities, we are going to implement the two functions in a very simple way. Check the full code for this tutorial bellow, with both our tasks implemented.This will allow us to store more complex messages in queues, facilitating the process of inter-task communication.
This will allow us to store more complex messages in queues, facilitating the process of inter- task communication. In our program, we will focus on the process of inserting and consuming items from the queue. Thus, we will create a simple data struct, create some variables of that data type, insert them in the queue and then consume them.
Our data struct will represent an IoT sensor measurement. In a real application use case, we could have, for example, one task or multiple obtaining measurements from different devices and then sending them to a dispatcher task that would send the measurements to the cloud. The first thing we are going to do is declaring our struct. As mentioned, we will create a testing struct that represents an IoT sensor measurement, just for demonstration purposes.
For a more detailed tutorial about using structs on the Arduino environment, please consult this blog post. Our struct will be equal to the one presented on the mentioned tutorial and will have three fields: a device ID, a measurement type and a measurement value.
The first two members will be of type int and the third will be of type float. Moving on to the Arduino setup function, we will open a serial connection, in order to output the results of our program and obtain them on the Arduino IDE serial monitor when testing the code.
This function receives as first input the maximum number of items that the queue can hold and as second input the size, in bytes, of an element of the queue . All the elements of the queue should have the same size. For the first argument, we will pass the value 10, which means that the queue can hold, at most, 10 items at a single time. You can test with other value if you want. The size of each item will be equal to the size of the structure we have previously declared. To get its value, in bytes, we can use the sizeof function.
This type corresponds to the type of the global variable we declared at the beginning of the program and so we will assign result of the function to that variable. Thus, we will do an error checking a print a message in case the queue was not created. Moving on to the Arduino loop function, we will start to insert items on the queue. We will do this in a loop with 10 iterations, which corresponds to the size of the queue. In each iteration, we will create a variable with the type of our struct and assign values to its fields.
We will assign the current iteration value to the deviceId field, so it varies for each message. As first argument, the function receives the queue handle we previously obtained. As second argument, it receives a pointer to the item we want to insert. Note that even tough we are passing a pointer to the item, it will actually be copied into the queue , not just referenced.
In our case, it means that the whole struct will be copied into the queue. For larger data structures, it may be a better option to use the queue to store references to those structures, but that is a more advanced use case that we will not cover here. The last argument corresponds to the maximum amount of time the task should block waiting for space to become available on the queue, in case it is full, to be able to insert the item . Nonetheless, we will design or program flow in such a way that ensures this never happen.
Now that we have an insertion loop, we will also design a similar consumption loop, to get the inserted items and print their values to the serial port.If you've got a moment, please tell us what we did right so we can do more of it. Thanks for letting us know this page needs work. We're sorry we let you down. If you've got a moment, please tell us how we can make the documentation better.
Installing software on the host machine for developing and debugging embedded applications for your microcontroller board. Loading the application binary image to your board, and then running the application.
Interacting with the application running on your board across a serial connection, for monitoring and debugging purposes. Browse to the IAM consoleand from the navigation pane, choose Users. Do not proceed to the Get Started section of the Espressif guides.
Instead, follow the steps below. To set up the toolchain, follow the instructions for your host machine's operating system:. Standard Setup of Toolchain for Windows.
Standard Setup of Toolchain for macOS. Standard Setup of Toolchain for Linux. Version 3. You must use the compiler that is compatible with version 3. To check the version of your compiler, run "xtensa-espelf-gcc --version". FreeRTOS supports versions 3. You can download the latest version of CMake from CMake. Both source and binary distributions are available. You can download these drivers from Silicon Labs. You can download these drivers from FTDI. After you establish a serial connection, make a note of the serial port for your board's connection.
You need it when you build the demo. If you are running macOS or Linux, open a terminal prompt.
If you are running Windows, open mingw To verify that you have Python 2. The version installed is displayed. If you do not have Python 2. On macOS or Linux, run pip install tornado nose --user and then run pip install boto3 --user.
Make sure that you use forward slashes to specify this path. For more information about SetupAWS. You must run CMake commands in a native Windows environment like cmd or powershell. If you want to consume FreeRTOS in your own CMake project, you can set it up as a subdirectory and build it together with your application. If you're using git, you can also set it up as a git submodule with the following command so it's easier to update in the future.
Here's an example of the top-level CMakeLists. To build the project, run the following CMake commands. After running CMake, you can find all available components in the summary output. It should look something like this:.A UART provides a widely adopted and cheap method to realize full-duplex or half-duplex data exchange among different devices.
ESP32 Arduino: Using structs as items in FreeRTOS queues
Each UART controller is independently configurable with parameters such as baud rate, data bit length, bit ordering, number of stop bits, parity bit etc. The overview reflects a typical programming workflow and is broken down into the sections provided below:. Setting Communication Parameters - Setting baud rate, data bits, stop bits, etc.
Setting Communication Pins - Assigning pins for connection to a device. Using Interrupts - Triggering interrupts on specific communication events. Steps 1 to 3 comprise the configuration stage. Step 4 is where the UART starts operating. Steps 5 and 6 are optional. This identification is needed for all the following function calls. UART communication parameters can be configured all in a single step or individually in multiple steps.
See the example below. Configure specific parameters individually by calling a dedicated function from the table given below. These functions are also useful if re-configuring a single parameter. Once this step is complete, you can connect the external UART device and check the communication. The function will copy the data to the Tx ring buffer either immediately or after enough space is availableand then exit.
The code below demonstrates the use of this function. Instead, it will write all data which can immediately fit into the hardware Tx FIFO, and then return the number of bytes that were written. An example of using these functions is given below. The UART controller supports a number of communication modes. There are many interrupts that can be generated following specific UART states or detected errors.
The API provides a convenient way to handle specific interrupts discussed in this document by wrapping them into dedicated functions:.
FIFO space threshold or transmission timeout reached : The Tx and Rx FIFO buffers can trigger an interrupt when they are filled with a specific number of characters, or on a timeout of sending or receiving data. To use these interrupts, do the following:. It can be used, e. The following functions are available:. The API also defines several macros. The term collision means that a transmitted datagram is not equal to the one received on the other end.
Data collisions are usually associated with the presence of other active devices on the bus or might occur due to bus errors. The collision detection feature allows handling collisions when their interrupts are activated and triggered. In the case of using circuit A or B, the RTS pin connected to the DE pin of the bus driver should be controlled by the user application.
ESP32 Arduino: Creating a FreeRTOS task
To use this mode, the software would have to disable the hardware flow control function. This mode works with all the used circuits shown below.Queues are very useful for inter-task communication, allowing to send messages from one task to another safely in terms of concurrency . You can check the queue API here.
One very important aspect to keep in mind is that the data that is inserted in the queue is copied rather that only a reference to it being stored . This means that if we send an integer to the queue, its value will be actually copied and if we change the original value after that no problem should occur. Nonetheless, we can still insert pointers to data as elements of our queue, which is useful specially if the messages to exchange are big.
In this case, the pointer will be copied to the queue, not the message itself, and thus we need to guarantee that it is not changed.
ESP32 : Inter task communication using FreeRTOS Queues
But this is a more advanced situation which we are not going to cover here. Other important behavior to keep in mind is that the insertion in a full queue or the consumption of an empty queue can be made blocking calls for a specified amount of time  this amount of time is a parameter of the API.
Although as mentioned queues are typically used for inter-task communication, for this introductory example we will insert and consume elements in the queue on the Arduino main loop function, in order to focus on the basic API calls we need to do. For this tutorial we will not need any additional libraries. Moving to the setup function, we will start by opening a serial connection, which we will use to output the results of our program.
This function receives as first input the maximum number of elements the queue can hold at a given time and as second argument the size in bytes of each element . Note that each element of the queue should have the same size . So, we will create a queue that can hold a maximum of 10 elements and since it will contain integers, we can get the size of an integer in bytes with a call to the sizeof function. In case a problem with the allocation of the queue occurs, it will return NULL .
Thus, we will also do a NULL check on the setup function and warn the user if a problem has occured. Moving on to the main function, we will now start by inserting the values in the queue for later consumption. This function receives as first input the queue handle , which will be the global variable we declared and assigned with the result of the call to the queue creation function.
As second input, it receives a pointer to the item we want to insert remember, although we are passing a pointer, the item will actually be copied and as last argument the maximum amount of time the task should block waiting, in case the queue is full .
Nonetheless, given the way we will build the program, we will never try to insert when the queue is full, so the main loop will never block. Since our queue can hold a maximum of 10 elements, we will do a simple for loop and at each iteration we will insert the current value. Note that we are always passing a pointer to the same variable but since its actual value will be copied, there is no problem in changing it to a new value in each iteration, as we will confirm when running the code.
We will follow the same loop approach to consume the items of the queue. So, to consume an item, we simple need to call the xQueueReceive function. It will receive as first input the handle for the queue, as second input a pointer to a buffer to where the received item will be copied and finally the number of ticks to wait in case the queue is empty. As for the buffer to which the item gets copied, we need to declare a variable of type integer prior to the consumption of the item, which we will use to store the received item.
Note that upon the consumption of the item, it will be removed from the queue. In our loop to consume the elements, we will also print them to the serial port, as can be seen bellow. The full source code can be seen bellow.
We also do a null check at the beginning of the Arduino main loop to avoid operating on the queue if it has not been allocated. We also added a delay between each iteration of the main loop. To test the code, simply compile it and upload it with the Arduino IDE. Then, open the serial monitor, with a baud rate equal to the one specified in the begin function You should get an output similar to figure 1, which shows the queue inserted items being printed in each iteration of the main loop function.
Figure 1 — Output of the queue example program. Skip to content.Return pdPASS if the task was successfully created and added to a ready list, otherwise an error code defined in the file projdefs. Tasks must be implemented to never return i. This is mainly used to facilitate debugging. Values 0 or 1 indicate the index number of the CPU which the task should be pinned to. The second block is used by the task as its stack. If a task is created using xTaskCreate then both blocks of memory are automatically dynamically allocated inside the xTaskCreate function.
If a task is created using xTaskCreateStatic then the application writer must provide the required memory. If neither pxStackBuffer or pxTaskBuffer are NULL, then the task will be created and a task handle will be returned by which the created task can be referenced. See the configuration section for more information. The idle task is responsible for freeing the kernel allocated memory from tasks that have been deleted. It is therefore important that the idle task is not starved of microcontroller processing time if your application makes any calls to vTaskDelete.
Memory allocated by the task code is not automatically freed, and should be freed before the task is deleted. Passing NULL will cause the calling task to be deleted. The actual time that the task remains blocked depends on the tick rate.
For example, specifying a block period of ticks will cause the task to unblock ticks after vTaskDelay is called. It does this by specifying an absolute time rather than a relative time at which the calling task should unblock.
This function differs from vTaskDelay in one important aspect: vTaskDelay will cause a task to block for the specified number of ticks from the time vTaskDelay is called. It is therefore difficult to use vTaskDelay by itself to generate a fixed execution frequency as the time between a task starting to execute and that task calling vTaskDelay may not be fixed [the task may take a different path though the code between calls, or may get interrupted or preempted a different number of times each time it executes].
Whereas vTaskDelay specifies a wake time relative to the time at which the function is called, vTaskDelayUntil specifies the absolute exact time at which it wishes to unblock. The variable must be initialised with the current time prior to its first use see the example below. Following this the variable is automatically updated within vTaskDelayUntil. Calling vTaskDelayUntil with the same xTimeIncrement parameter value will cause the task to execute with a fixed interface period.
Passing a NULL handle results in the priority of the calling task being returned. Return The state of xTask at the time the function was called. Note the state of the task might change between the function being called, and the functions return value being tested by the calling task. A context switch will occur before the function returns if the priority being set is higher than the currently executing task.
Passing a NULL handle results in the priority of the calling task being set. When suspended, a task will never get any microcontroller processing time, no matter what its priority.
Calls to vTaskSuspend are not accumulative - i. Passing a NULL handle will cause the calling task to be suspended. A task that has been suspended by one or more calls to vTaskSuspend will be made available for running again by a single call to vTaskResume. Use of a semaphore as a synchronisation mechanism would avoid this eventuality.
After calling vTaskSuspendAll the calling task will continue to execute without risk of being swapped out until a call to xTaskResumeAll has been made. Restart the kernel. It does not unsuspend tasks that were previously suspended by a call to vTaskSuspend. Return The count of ticks since vTaskStartScheduler was called.
Return The number of tasks that the real time kernel is currently managing. This includes all ready, blocked and suspended tasks. A task that has been deleted but not yet freed by the idle task will also be included in the count. Return The text human readable name of the task referenced by the handle xTaskToQuery.