Why does an USB CDC device require a host driver in windows?
Usually on Home windows the “driver” for a USB serial system is not more than an inf file that maps the system VID/PID to the Microsoft usbser.sys CDC/ACM driver.
Latest releases of Home windows 10 seem to have stopped insisting that every CDC/ACM have a VID/PID particular inf file, and can load the usual driver for any system that presents as a CDC/ACM system.
The benefit of getting a VID/PID particular inf file is that your system can have a vendor particular “pleasant title” which can be utilized in functions to extra simply establish your system, quite than simply showing as a generic “USB Serial Machine”.
One drawback with Microsoft’s usbser.sys driver (and Linux and Mac OS aren’t any completely different) till just lately was that when you disconnect the USB system, the motive force is unloaded even when an utility has the COM port open, and the applying should shut and reopen the port to get well when reconnected. I’ve beforehand used a customized driver (supplied by a 3rd get together), that doesn’t unload if an utility has the port open, in order that when the USB cable is reconnected, the info connection continues as regular, simply as it could if it had been an RS-232 cable. Nevertheless, once more in latest variations of Home windows 10 I’ve observed that usbser.sys seems to exhibit this behaviour in any case.
Notice that once you do present your personal driver file, and even only a customized inf file, you can be required to undergo WHQL testing to ensure that your system to be allowed on Home windows 10, or to load with out warnings on earlier variations. To do that you’ll want a USB.org assigned VID, an Prolonged Validation code-signing certificates, and both the instruments and amenities to carry out the testing, or pay a take a look at home to carry out the testing. That each one will get considerably costly, and could also be prohibitive for low quantity, low worth or non industrial merchandise.
At one time Microsoft too charged for WHQL processing submissions, however not achieve this. That’s nevertheless little mixture since on the identical time they modified to requiring an EV certificates and stopped a deal the used to have for low-cost certificates.
The benefit of WHQL qualification is your driver might be supplied by Home windows Replace.
If you’re utilizing a USB serial bridge chip quite than your personal USB stack and USB controller, then there’s a decrease value resolution. These chips may be customised with your personal VID/PID and descriptors, and the seller’s present WHQL may be related to your system so that you get all the benefits of your personal driver with out the prices. Most distributors will even assist you to use their VID and can assign you a singular PID so you may keep away from USB.org charges. I’ve used this route with each Prolific and FTDI units; it’s by far essentially the most value efficient resolution.