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List:       libusb-devel
Subject:    Re: [Libusb-devel] How to send/receive data using gadgetfs bulk
From:       Alan Stern <stern () rowland ! harvard ! edu>
Date:       2011-12-15 19:09:21
Message-ID: Pine.LNX.4.44L0.1112151400370.1644-100000 () iolanthe ! rowland ! org
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libusb-devel is not the appropriate mailing list for this discussion, 
as gadgetfs has no connection with libusb.  If you have further 
questions, please send them to <linux-usb@vger.kernel.org>.

On Thu, 15 Dec 2011, Winson Yung wrote:

> Thanks Alan, indeed I re-used the file handles (for en1in-bulk and
> en1out-bulk) opened by ep_config, but first write to source_fd just
> got stucked forever.

It won't return until the host reads the data you are trying to send.

> Also, in the ep_config(), the comment says 1 for fs or hs, 2 for fs +
> hs like the following code:
> 
> 	/* one (fs or ls) or two (fs + hs) sets of config descriptors */

Read it more closely.  It doesn't say "1 for fs or hs, 2 for fs + hs".  
It says one set of descriptors for fs or ls, and two sets of 
descriptors for fs + hs.

> 	*(__u32 *)buf = 1;	/* tag for this format */
> 	memcpy(buf + 4, fs, USB_DT_ENDPOINT_SIZE);
> 
> 	if (HIGHSPEED)
> 		memcpy(buf + 4 + USB_DT_ENDPOINT_SIZE, hs, USB_DT_ENDPOINT_SIZE);
> 
> 	status = write(fd, buf, 4 + USB_DT_ENDPOINT_SIZE
> 			+ (HIGHSPEED ? USB_DT_ENDPOINT_SIZE : 0));
> 
> Should the code be written like this?
> 
> 	if (HIGHSPEED) {
> 		*(__u32 *)buf = 2;	/* tag for this format */
> 		memcpy(buf + 4 + USB_DT_ENDPOINT_SIZE, hs, USB_DT_ENDPOINT_SIZE);
> 	}

No, it shouldn't; it should be written the way it _is_ written.  If you
want to run at high speed, you must provide two sets of descriptors:
one for full speed and one for high speed.  This is required by the
USB-2.0 spec: Any device capable of connecting at high speed must also
be capable of connecting at full speed.

> Since I was trying to use the highspeed bulk xfer, I tried changing
> tag format to 2, and I got this error:
> 
> simple_source_thread config ep1in-bulk error 22 (Invalid argument)
> simple_sink_thread config ep1out-bulk error 22 (Invalid argument)

That's not surprising, since 2 is not a valid tag value.

Alan Stern


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