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STM32 FreeRTOS Series Part 1: Mastering Tasks & Priorities in STM32CubeIDE
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Sep 27, 2019
Welcome to **Part 1** of our STM32 FreeRTOS series! In this tutorial, we dive into the essentials of integrating FreeRTOS with STM32CubeIDE. You'll learn how to: * Set up FreeRTOS in STM32CubeIDE * Create and manage tasks * Assign task priorities for efficient multitasking * Utilize the FreeRTOS kernel for real-time applications([mongoose.ws][1]) **🔗 Download the Project Code:** Access the complete project code and configuration files here: [ https://controllerstech.com/introduction-to-free-rtos-in-stm32/] **📺 Continue Your Learning:** Dive deeper into FreeRTOS with Part 2 of this series: [https://youtu.be/k_fHypOMk9s] #STM32 #FreeRTOS #STM32CubeIDE #EmbeddedSystems #RealTimeOperatingSystem #Microcontrollers #TaskManagement #EmbeddedDevelopment #STM32Tutorial #FreeRTOSSTM32
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0:08
hello
0:09
everyone welcome to controllers Tech
0:13
today in this video I am going to
0:15
introduce you guys to the concept of
0:19
R A realtime operating system is a very
0:23
important part of embedded
0:25
systems the main idea behind our to is
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to perform multiple tasks at the same
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time today I will show you the benefit
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of using an OS how to create tasks in
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freeer and how to handle
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priorities I am using stm32 Cube ID and
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I will start by creating a project in
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Cube MX
1:18
I am choosing version one because it is
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supported by majority of the
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microcontrollers in the setting leave
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everything as it is make sure that the
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preemption is in
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enabled we will use preemption based
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scheduling in which a higher priority
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task can take control from a lower one
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you can Google about it go to tasks and
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cues Tab and here you will see a
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predefined
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task here you will see some details
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about it its name priority level stack
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size entry
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function I will explain all these along
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the video
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I will create one task here and another
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one in the program
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itself I am going to name it as task 2
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its priority will be normal stack size
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is
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128 and entry point will be task 2 in it
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everything else unchanged and task is
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created this is it for the free rtos
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part the rest of the setup is as
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usual I am also using you up to show the
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importance of priority
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levels let's set the clock for the
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maximum clock
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and everything is done click save so we
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got a warning saying that we shouldn't
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use CIS tick with the AR
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toes so go to sis and change the time
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base to any timer
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I am also using these two pins as output
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to demonstrate some stuff click save now
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and code should
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generate open the main. C
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file first I will explain some r related
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things OS thread ID stored the unique ID
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of the thread all the operations that we
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will do related to any thread will
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require this
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ID next the entry points of the thread
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that we created are
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defined these are basically the main
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functions of the
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tasks you have to write your task
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related code in it next inside the main
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function the main task is created
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first the task is defined and then it is
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created o thread death takes the
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following
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arguments the first is the name of the
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task then the entry point of the
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task then the priority of the
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task then the instance and the stack
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size once the task is defined we need to
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create it using OS thread create
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function
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and after successful creation the thread
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ID is stored in the relevant variable
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that we defined in the beginning at last
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OS kernel start is
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called after this point the scheduler
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will overtake and the control does not
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reach beside this line I will
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demonstrate that in a while if you
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scroll down you will see that the entry
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points are defined here like I said we
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have to write our code in these
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functions I will do that in few
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minutes but let me start by writing the
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code inside the while loop so here I
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will try to toggle PA a0 and pa1 after
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some delay
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so compile the
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code there are no
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errors let's debug
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it choose SDM 32
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application we don't need to modify
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anything just choose okay
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[Music]
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fine let's run it and see so as expected
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there is no movement on the
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oscilloscope like I mentioned once the
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kernel starts the shedul takes over and
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the control doesn't reach the while
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loop so I will comment out the line here
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so the colonel don't
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start let's run the program
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again yeah so we have a wave with time
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period of around 5
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milliseconds actually what I wanted to
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do is to generate a wave of 1
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millisecond on PA a0 pin and another
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wave with the period of 2 milliseconds
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on pa1 pin but obviously it's not going
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to happen by simply writing in a while
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loop so here comes the RTO
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in the default task I am going to toggle
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the pin pa0 with a period of 1
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millisecond and in the task two toggle
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the pin pa1 with a period of 2
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milliseconds at this point scheduler
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know what I
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want and it's going to schedule the
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entire process in a way that every task
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gets the time they the defined for let's
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compile and run it
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right now the pin is connected to pa0
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and you can see that the period is 1
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millisecond now I am switching the PIN
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to pa1 and the period changes to 2
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milliseconds so here both the tasks even
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with a delay as small as 1 millisecond
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can run simultaneously
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this is the benefit of using our T over
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a simple
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programming but obviously this is not it
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let's see the basic most types of
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problems that we face with the
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RT let me explain you the role of
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priorities now first I will Define a
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function to send some data to the
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uart this function is supposed to run
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only in the default
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task I will Define another function to
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send data to you art and this one will
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run into task two before proceeding any
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further I will create another task here
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to do so first we have to create a
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thread ID for the
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task then we have to create an entry
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function for the
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task I will name it as task three in it
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next inside the main function we have to
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define the thread
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first so OS thread def is used and the
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parameters will be the name of the task
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the entry point of the task the priority
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instance and at last the stack
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size then we will create the thread and
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assign the ID to the task 3
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handle and at last write some code in
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the entry function of the task make sure
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that you write everything in a while
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loop these tasks are not defined to
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handle return so you should always have
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everything inside an infinite
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Loop just like the other two I am also
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going to write one you out function for
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the third
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task it's time to write our code now so
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the default task is going to send the
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data to the uart every 1
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second and task two is going to send the
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data every 2
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seconds let's compile this and see how
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the RT handles this
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situation as you can see that each task
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is printing every second but this is not
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what we opted for we wanted the default
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task to print every second and tasked
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two to print every 2
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seconds let's test this between the
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default task and the task three which
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runs every 3 seconds
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okay as you can see the default task
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prints twice and then in the third
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second both default and task three
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prints together here the code works all
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right because the delay is
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large but what if the time delay is same
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for all the
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tasks so here I will use all three tasks
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to transmit with the same delay of 1
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second let's compile the code and debug
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it as you can see even though the data
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is being transmitted it's not what we
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were looking
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for every task Waits 3 seconds to
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transmit again but we wanted all of them
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to transmit every 1
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second this happens because they all are
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sharing the same
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art to avoid these situ situations with
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the shared resources we will use the
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priorities currently they all have the
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same
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priorities I will change the priority of
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task two to the above normal and the
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task one to below normal so finally we
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have three tasks all with different
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priorities and sharing the same resource
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let's see what happens
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now as you can see now that all three of
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them are printing at the same time and
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every 1
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second this is exactly what we were
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looking for also note that tasked two
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prints first then default task and at
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last task three the reason behind this
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is the task 2 priority is highest as it
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is above normal then default task which
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is normal and at last task three which
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is below normal so they are executed in
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the same order as their
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priorities this is it
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guys I hope you understood some basic
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concepts here this was just the
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introduction about what our to is on how
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to handle some basic function in it I
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recommend that you read about our
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to we will continue this series of
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tutorials time to time you can download
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the code from the link in the
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description
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