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FreeRTOS Tutorial 6 || Structured Queue || Memory Allocation || STM32
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Apr 10, 2020
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View Video Transcript
0:07
hello everyone welcome to controllers
0:11
Tech in my previous video about free RT
0:15
OS I covered how to send or receive data
0:18
using q AK you can only hold the data of
0:22
same type if we want to transfer the
0:26
data of different types we have to use
0:28
structure q and in this video we are
0:31
going to discuss about it we will start
0:34
by creating the project in cube ide
0:37
[Music]
0:42
select the controller you are using give
0:50
some name to the project and click
0:53
finish
0:56
[Music]
0:59
in the cube MX first of all I am
1:03
selecting external crystal for the clock
1:09
[Music]
1:14
go to cysts and select the time-base
1:18
anything other than cystic I am
1:21
selecting timer six you are to is to
1:24
communicate with the computer
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[Music]
1:40
select the free Artie OS version one and
1:43
leave everything as it is
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[Music]
1:55
this default task will be created and we
1:59
will deal with it later now go to the
2:02
clock setup the crystal is 8 megahertz
2:04
and I want the controller to run at 180
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megahertz
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click Save to generate the project
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[Music]
2:24
I am NOT going to use the CMC's API so
2:31
go to see MCH file and copy all these we
2:36
will include them directly in our
2:38
project comment out the CM sis file we
2:46
will remove the default task related
2:47
functions which were generated by
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default
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[Music]
3:02
let's start with the coding now first it
3:11
find the Q handler next we need to
3:20
define the task handlers I will be using
3:24
to sender tasks and one receiver task
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like I said in the beginning that we
3:36
will be sending different data types to
3:39
the same queue to do that we need to
3:42
create a structure of all those data
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types I am creating this structure which
3:48
have a pointer to the character an
3:49
integer and an unsigned 16-bit integer
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let's call it my struct these will be
4:01
required to inside the main function we
4:09
first need to create a queue that can
4:12
hold the structure type this queue can
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store two elements which are of the type
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my struct
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these string will be printed based on if
4:38
the queue was created or not
4:46
after creating queue we will create the
4:49
tasks
4:58
looks like I forgot to define the task
5:01
functions let's define them now
5:13
these functions are where the
5:15
task-related code will be written
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[Music]
5:27
X tasks create takes the following
5:30
parameters task function some name of
5:34
the task stack depth the parameter to
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the task the priority of this task and
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the handler of this task note that I am
5:47
using same priority of two for both the
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sender tasks receive a task have lower
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priority after creating the tasks we
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will start the scheduler now let's write
6:06
the codes for these tasks first the
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sender one task I am declaring a pointer
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to my struct this is to convert the
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delay to ticks when the control enters
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the task this string will be printed on
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the console now before assigning the
6:29
data we must allocate the memory for
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this pointer to the structure
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[Music]
6:38
to do so we will use PV port malloc
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function it's defined in the portable
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dot H file it's takes size as the
6:52
parameter there is also V port free to
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free the allocated memory I am guessing
6:59
you are already familiar with the malloc
7:01
function PV port malloc is also the same
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but you can consider it as safer when
7:07
using the free RTOS the size of memory
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we need is same as the size of my struct
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[Music]
7:22
now we will load the data to the
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structure
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[Music]
7:43
and then send this data to the queue
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[Music]
7:54
XQ cent takes the following parameters
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the handler of the queue the address of
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the data and the amount of time to wait
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if the queue is full
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if the data is successfully sent to
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queue it will return PD pass
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[Music]
8:18
and this string will be printed to the
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console let's make it a bit more
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interesting index 1 will be incremented
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by 1 each time the control enters this
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task these values will be modified based
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on this index 1 value and at last this
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task will go into suspension for 2
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seconds
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similarly send a task 2 will also send
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the data to the queue every 2 seconds
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[Music]
9:00
now let's write the receiver task
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[Music]
9:09
our PTR to struct is another pointer to
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my struct this is where the received
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data will be stored converting three
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seconds to tix this string will be
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printed when the control enters the
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receiver tasks now we will receive the
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data from the queue xq receive takes the
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following parameters the handler of the
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queue address of the variable where the
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data should be stored and the wake time
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in case the queue is empty it will
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return pd pass if the data is received
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from the queue here we will allocate new
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memory location to store the string I am
10:02
expecting the size of string could be
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100 bytes whenever you are using s print
10:08
F in the free rtos make sure you
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allocate the memory like this otherwise
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s printf will cause hard fall to error
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this string will be stored in the PTR
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pointer location
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and we will send this string to the UART
11:05
[Music]
11:12
after sending free the location of the
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PTR that we just created we must also
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free the memory that we allocated in
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both the sender tasks so we will use V
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port free and the argument will be the
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our PTR to struct this way the memory
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will be free for the pointer which was
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received by the queue and the other
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pointer will be safe I will demonstrate
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this in a while we also need to include
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the SD d i/o for the s printf and string
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dot H for the string related functions
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let's build this code now there are no
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errors so we will debug the code I am
12:01
using Hercules for the serial console
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let's run this now I am going to let it
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run for a while
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[Music]
12:35
so the queue was created successfully it
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entered the sender to task sent the data
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to the queue and task dot suspended
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somehow the data is not printing
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properly here so we will just look at
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the received data data from sender one
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is printed data from sender two again
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from sender one with new counter value
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of two and large value increased same
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result from the sender to task let's run
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it freely as you can see the values are
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printing from both the tasks also the
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counter is increasing and so is the
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large value send a one sender two now
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let's see how the memory allocation
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works
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[Music]
13:42
reset the debugger
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[Music]
13:52
I will put a breakpoint here and here
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and here
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[Music]
14:12
note that I am watching this in the
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variables tab and not in the live
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expression we hit the first breakpoint
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keep an eye at the PT artis struct it's
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showing zero right now when I stepped
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over this function memory gets allocated
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for the PT artis struct the location for
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this memory is heat plus 1964 we will
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just consider it as 1964 let's run the
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code again we hit another breakpoint in
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send a to task step it over the memory
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PT artis struct is now 1988
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[Music]
15:15
[Music]
15:20
now we hit the breakpoint in the
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receiver task note the PTR variable
15:31
the memory allocated for it is 2012 also
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our PTR to struct have the data from
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memory 1964 which is associated with
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sender 1 PTR to struct right now
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[Music]
15:54
[Music]
15:59
[Music]
16:06
let's add another breakpoint here we
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have already freed the memory of PTR so
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2012 location is free now if we step
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over this sender one PTR to struct is
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also freed now if we run the code now we
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hit the sender 1 breakpoint again as the
16:27
memory 1964 was free it will be
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allocated to sender one again let's run
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it we hid the sender to breakpoint the
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memory 1988 is already occupied and next
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free slot is 2012 here 2012 will be
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allocated for the sender to PTR 2 struct
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guys this is just the memory allocation
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as the queue already have two waiting
17:00
elements so send a to can't send the
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data to the queue right now we are in
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the receiver task right now note that
17:09
our PTR 2 struct have the data from the
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memory location of 1988 which was
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allocated to sender to task before PTR
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was allocated the memory of 2036 and was
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freed in the previous step after running
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this statement memory location of 1988
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which was associated with the sender to
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task is also freed again we are in the
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sender 1 task the lowest slot available
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right now is 1988 and this will be
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allocated to the sender 1 PTR 2 struct
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this is how the memory allocation works
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as I mentioned we free the memory after
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receiving the data and this way only the
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memory allocated to the pointer that we
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received gets free and other data
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remains safe this is it guys I hope you
18:06
understood the concept of structured
18:08
queue and how to use the memory
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allocation in free RT OS
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you can download the code from the link
18:16
in the description leave comments if you
18:19
have doubts be safe and don't step out
18:23
of your home have a nice day
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