Re: usb 1-3: Product: BBC micro:bit CMSIS-DAP not recognised

[Dmitrii Pasechnik <dima.pasechnik@cs.ox.ac.uk>]

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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@rowland.harvard.edu> 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

HTH,
Dmitrii

> 
> Alan Stern

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