On Fri, Dec 23, 2022 at 11:41:03PM +0000, Dmitrii Pasechnik wrote: > On Fri, Dec 23, 2022 at 09:52:50AM -0500, Alan Stern wrote: > > On Fri, Dec 23, 2022 at 12:58:41PM +0000, Dmitrii Pasechnik wrote: > > > On Thu, Dec 22, 2022 at 04:24:55PM -0500, Alan Stern wrote: > > > > A bit off to the side from the main point of this thread, but... > > > > > > > > On Thu, Dec 22, 2022 at 10:32:09AM +0000, Dima Pasechnik wrote: > > > > > > > > > > > > > > > On 20 December 2022 19:57:05 WET, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > > > > > >> USB Interfaces: MSD, CDC, HID, WebUSB > > > > > > > > > > > >Which agrees with the information on the web site. I have no idea what > > > > > >WebUSB is supposed to be. > > > > > > > > > > WebUSB is a JavaScript API, supported by Chromium -derived browsers (Firefox not there yet) > > > > > > > > > > https://en.wikipedia.org/wiki/WebUSB > > > > > > > > The Wikipedia article agrees with you that WebUSB is a JavaScript API. > > > > As such, it is used for communication between web browsers and > > > > JavaScript programs. > > > > > > No, it's used by browsers (which run JavaScript code in them) to > > > communicate with USB hardware. Or, if you like, > > > standalone JavaScript programs to communicate with USB hardware. > > > Let me copy from the wiki here: > > > > > > --------------------------------- > > > A Universal Serial Bus, or a USB is an industry standard [...] > > > WebUSB is a set of API calls that enable access to these hardware > > > devices from web pages. WebUSB is developed by the World Wide Web > > > Consortium(W3C).[1] The webUSB API provides a safe, and developer > > > familiar means of communication to edges devices from web pages. The > > > webUSB API integrates into existing USB libraries and shortens the > > > development cycle for integrating new devices into the web environment > > > by not needing to wait for browser support for these devices. > > > > > > Early versions of webUSB came out around as an alternative to Flash, > > > Chrome Serial, and other custom approaches to connecting browsers to > > > hardware. WebUSB aims to solve the four goals of any interface being; > > > fast to make, cross platform, look good, accessibility. > > > > > > > Not for communication between programs and USB > > > > devices. So I don't understand why a USB device needs to be concerned > > > > about it. > > > > > > I hope the above explains. > > > > Actually, it's ambiguous. > > > > The article says that WebUSB is an API used by JavaScript programs when > > they want to interact with a USB device. Which means it is something > > that JavaScript programs can know about and interact with. Fine. > > > > But the article doesn't say what happens on the device's side of the > > conversation. Does the WebUSB framework use some special messages when > > communicating with a USB device, so it will only work with devices which > > support WebUSB's protocol, or does it use plain ordinary USB messages > > which any USB device will support? > > > > To put it another way, do USB devices need to have specialized firmware > > in order to be compatible with WebUSB, or will WebUSB work with all USB > > devices? If the latter is true then why does the BBC micro:bit device > > have a special WebUSB interface? Does the extra interface provide some > > sort of device-specific information which WebUSB can make use of but > > which isn't essential? > > here is what I could find about the device side of WebUSB: https://web.dev/build-for-webusb/ > Basically, WebUSB support offers some extras, e.g. one can get a > specific pop-up with a URL in it (supplied by the board) in the web browser as > the device is plugged in the USB port. > > Also, on the software side, this: https://developer.chrome.com/articles/usb/ > is more informative than the Wikipedia article. > And here is how WebUSB-capable device is meant to talk ot the machine > it's plugged in: https://wicg.github.io/webusb/#webusb-platform-capability-descriptor Those are very helpful, thank you. Interestingly, none of those documents mentions anything about having a special WebUSB interface in the configuration. The WebUSB information on a device is accessed using standard or vendor-specific control messages with the device (not an interface) as recipient. So the question of why the micro:bit has a WebUSB interface remains a mystery... Alan Stern
