On Monday 11 February 2008, Jean-Christophe Dubois wrote:
> On Saturday 09 February 2008 13:44:22 David Brownell wrote:
> >
> > Plus, as I noted, in the case of CDC-derived devices it *can't* compute
> > those values before bind().
>
> For my education, could you please elaborate a bit on why the CDC-derived
> devices *can't* compute those values before bind().
They use two interfaces (and potentially more):
- Control ... the one passed to probe(), possibly with one interrupt
endpoint used to send status to the host. Descriptors are coupled
to this interface, including the "union" descriptor (more below).
- Data ... the one with in/out endpoints (and sometimes, altsettings).
CDC Union descriptors are used to couple data interfaces to control
interfaces. The bind() is what parses the CDC descriptors then, among
other things, figures out which data interface to use ... and thus,
nothing before bind() can figure out which endpoints to use.
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