What is the exchange protocol of the usb com port?

Question

Drivers

Hello.
Using libusb, I'm trying to implement my own driver for the usb-com adapter, using the popular ft232 as an example.
I'm trying to receive data, for this I poll the endpoint, data comes in response, but before each portion there are bytes 0x31 and 0x60 - they definitely do not belong to the data. From this I conclude that these are some kind of "managers".
Are these bytes specific to the specific chip, or is it some kind of protocol? Where can you read about it?
PS speed settings, flow control has not yet been done, i.e. as the chip is connected, the polling for incoming data begins.

Answer 1

Greetings.
ft232 - it has its own driver and this driver creates a VCP (virtual com port), so when exchanging via usb there will be additional bytes, not like a racially correct CDC adapter.
See libFTDI sources, google ftdi_read_data_cb