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Re: STM32 USB support
- From: Simon Kallweit <simon dot kallweit at intefo dot ch>
- To: Andrew Lunn <andrew at lunn dot ch>
- Cc: Chris Holgate <chris at zynaptic dot com>, ecos-devel at sourceware dot org
- Date: Tue, 19 May 2009 17:16:47 +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> <20090519120004.GI20046@lunn.ch>
Andrew Lunn wrote:
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.
Chris, do you have any example code using your driver? I was wondering
if your approach to dynamically set the endpoint configurations should
be offered as an official alternative to the devtab entries (or we may
even get rid of the devtab entries). I may be working on USB serial and
ethernet support. The USB serial driver at least seems to be tailored
for the AT91 driver right now and cannot be used generically yet. We
could change that to use dynamic setup of endpoints, which I think would
be a great idea.