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Re: STM32 USB support
- From: Andrew Lunn <andrew at lunn dot ch>
- To: Chris Holgate <chris at zynaptic dot com>
- Cc: Simon Kallweit <simon dot kallweit at intefo dot ch>, ecos-devel at sourceware dot org
- Date: Tue, 19 May 2009 14:00:04 +0200
- Subject: Re: STM32 USB support
- References: <4A11CAAA.firstname.lastname@example.org> <4A11D861.email@example.com> <4A11E5DF.firstname.lastname@example.org> <4A129C34.email@example.com>
> >> There is a significant difference from the other USB drivers which I
> >> should probably flag up (and document). The endpoint configuration is
> >> generated dynamically from the USB descriptors. This gives a lot of
> >> flexibility and potentially allows support for multiple configurations
> >> (untested!). However, the downside is that I had to leave out devtab
> >> support since the devtab entries need to be set statically.
> > Don't you think it's possible to have both options? I haven't looked at
> > the USB subsystem or any drivers, but I think a public driver should
> > behave as the subsystem intends. Maybe the subsystem could be extended
> > for more dynamic usage though.
> The official docs say "To support this the device driver can provide a
> devtab entry for each endpoint". I took that to mean that devtab
> support was optional - and the dynamic endpoint configuration is a much
> more useful feature IMHO.
> Previously supported hardware has had fixed endpoint configurations
> which makes the static devtab entries easy to implement. However, with
> dynamic endpoint configuration, the low-level driver doesn't know
> a-priori what endpoints to generate devtab entries for - and nor should it!
The AT91 USB driver has something similar to this. It can configure
the endpoints by looking at the USB descriptors.
I don't remember how it works with respect to devtab entries.