On Fri, Jun 08, 2001 at 03:34:39PM +0100, Jerram, Simon wrote:
> Is there a decent specification available for this? If not...
>
> The Documentation for the URB API referrs to usb_control_msg
> as being a converter for the old API, and that it is a good
> exapmle on how to use the URB one. To an extent it is,
> but simply looking at it without any documentation on how
> you're supposed to use it doesn't help. The USB Programming
> guide is no help: it merely points to the routine with no
> indication of how it works, neither are any of the
> drivers I've looked at which are sparse on the code level
> documentaion and comments.
AFAIK there was no written documentation for the synchronous wrappers...
> OK.
>
> Now I want to send a control msg to which i expect a response.
>
> I use usb_control_msg which completes OK. But I can't tell where
> the response goes. Isn't usb_control_msg supposed to be synchronous?
int usb_control_msg(struct usb_device *dev, unsigned int pipe,
__u8 request,
__u8 requesttype,
__u16 value,
__u16 index,
void *data, <----- this is the data after the setup stage, either
written or read (depends on the requesttype)
__u16 size, <----- number of bytes you want to write/read after setup
int timeout)
Usually, you have only a setup stage, thus size and data can be 0, the setup
data is explicitely given with request*/value/index/size. When the
control_msg-call for a read completes successfully, you can expect your data
to be in data...
You should use only kmalloc-ed memory for that, stack space/heap/etc is
unreliable and may fail in future kernels.
> Do I need to use usb_control_msg again with an appropriate buffer to
> recieve the response? Or does it get placed in a structure that
> I should declared when I sent the control message? Tracing this through
> puts me at a dead end: the wake_up point simply seems to return the funtion.
I hope that helps a bit....
--
Georg Acher, [EMAIL PROTECTED]
http://www.in.tum.de/~acher/
"Oh no, not again !" The bowl of petunias
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