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everyone welcome to controllers tech
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this is yet another video in the usb
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and today we will see how to use
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communication class in usb
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i will show the working of both host and
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for the host i am using discovery f411
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and stm32f103 for the device
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let's start by creating a project for
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like i mentioned i am using discovery
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give some name here and click finish
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i will clear the pin outs first
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i am selecting the external crystal for
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in the usb otg setup set the mode as
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and also enable the v bus host is
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responsible to give the power to the
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and that's why we need the v bus to do
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you can see two pins for the usb and one
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bus got selected here this here is the
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schematics for this board
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as you can see v bus is connected to
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here which can be controlled from the pc
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pin when we pull the pc 0 to low
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the enable pin gets activated and so
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does the voltage to the v
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so i will set the pc 0 to low here
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now go to usb host and select the class
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as the communication host class
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click yes if there is a prompt
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you can see the v bus automatically took
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the pc0 as the solution
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now let's go to the clock setup
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it's already configured here so i don't
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click save to generate the project
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open the usb host.c file
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here we have different states for the
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usb and we need to use them in our
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i will copy this and the usb handle in
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make sure you define them as the
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let's include the usbcdc.h file
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as we need to use some of the functions
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you can browse the file like this
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here we have maximum limit for the
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and then we have all these functions
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that we will be using in our project
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i am going to define a smaller buffer
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size since i am only expecting a small
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we have some more variables here
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these are the transfer and the receive
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i have defined in cdc typedef here to
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switch between different states for the
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actually we won't need the send state i
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when the host is idle
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here is the cdc handler
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it will switch between different cdc
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if the state is idle it will stop the
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then copy the string into the transfer
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buffer and then transmit the data
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here the value will keep changing with
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if the data transmission is successful
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the state will change to receive
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and the variable will increment in the
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host will receive the data from the
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device and store it in the rx buffer
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here the data size is the size of the rx
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but it will only copy the amount the
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now we will wait for a second and switch
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the stake to idle for the next transfer
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in the while loop we will first check if
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the usb is ready for communication
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and if it is then call the cdc handle
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for processing the requests
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that's all for the host part now let's
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create another project for the cdc
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i am using stm32f103c8
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for the device give some name to the
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and click finish first of all
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i am selecting external crystal for the
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select this and serial wire debug
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now select the usb device and you can
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see the two pins got selected here
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and in the settings select communication
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and leave everything to default
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let's configure the clock now
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it has already configured it i will just
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push it to the max anyway
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that's all for the setup click save to
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here we will write our code in the usbd
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first of all we have to deal with the
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as you can see there are seven bytes
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let's create a buffer to store these
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cdc receive will be called whenever the
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and in the receive function we will
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transmit the same data back to the host
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i have defined a new length function
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because this function takes 16-bit
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whereas we have the pointer to a 32-bit
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no errors here so flash it to the board
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the flashing is done now let's go back
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i am going to put a break point here in
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the transmit function
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also i have added the rx buffer to the
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before starting it let's take a look at
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here you can see there is a usb
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connected between the host
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and the device also the device is not
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powered from anywhere
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else as the host will be responsible to
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that's basically all for the connection
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let's run it now it hit the break point
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that means the usb is ready for the
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it hit again and now we have received
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the data from the device
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the value in the data is incrementing as
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let's remove the break point and let it
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seems like it got stuck
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let's reset it and run again
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it's working pretty fine now
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there seems to be some extra characters
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i don't know where they are coming from
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i'll check and update if i make any
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anyway the code works well for the rest
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this is it for this video i hope you
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understood the process for both
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the host and the device you can download
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the code from the link in the
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keep watching and have a nice day ahead
