Posted on January 20, 2018 at 15:33USB can be very tricky to comprehend. A good place to start is
http://www.beyondlogic.org/usbnutshell/usb1.shtml#Introduction
. Apart from that you could read USB specification, but that is not so light reading. There is no, to my knowledge easy tutorial for the USB for the beginners. The best thing to do is just take some basic USB code and debug it.
Unlike UART or SPI or CAN, the USB has a lot of things on the low level that need to be done just to send a couple of bytes of data. Fortunately some of them are generated by CubeMX automatically.
There a few key parts of USB protocol.
1. USB Descriptors - these are data structures that describe how the device is implemented (how many interfaces it has, how many configurations, USB classes of the interfaces, etc.)
2. Endpoints - these are virtual channels for sending and receiving data to and from the device. Depending on the class of the device there can be 1 or more endpoints assigned to it.
3. Device classes - There are some standard device classes such as Mass Storage, CDC (Virtual Com Port), Audio Class etc., that help the host to find appropriate driver and in most cases the host can just use the generic driver, ie. the Mass Storage Class device can be automatically recognized and used without any special driver
4. Host driver - Every device should have compatible driver on the host side, which can be problem when writing your own device class
That being said, why do you need isochronous device? Unless you are making a Video or Audio device, thera are nott many host drivers that support isochronous transfer which means you would need to write your own host driver.
My suggestion is to start small with CDC class driver generated from cube and continue from there.
Regards
