Re: [Libusb-win32-devel] Read/write and release/claim_interface

[Stephan M. <ste...@we...>]

I don't think that your problems are cause by release/claim_interface.
These commands don't send any data to the device. They just lock
some resources (the interfaces) in the driver.

I think the problem seems to be the set_altinterface command.
Does your firmware properly handle a set_interface request? 
Does it reset the endpoint's data toggle bits when it receives 
such a request?

Stephan


> Hi
> 
> I don't understand the behavior of subsequent read/write operations when using usb_release_interface() and usb_claim_interface() between the read/writes.
> My test device is a AT90SUB1287 and loops the data from an OUT bulk endpoint to an IN bulk endpoint.
> I'm using the latest CVS source, but I had the same problem with the official libusb-win32-snapshot 20060827.
> 
> This scenario works fine:
> ****************************
> - usb_open()
> - usb_set_configuration()
> - usb_claim_interface()
> - usb_set_altinterface()
> 	- usb_bulk_write()	(multiple read/writes work fine)
> 	- usb_bulk_read()
> - usb_release_interface()
> - usb_close()
> 
> This scenario gives me a timeout error, but read/write work after some timeout errors again:
> ****************************
> - usb_open()
> - usb_set_configuration()
> - usb_claim_interface()
> - usb_set_altinterface()
> 	- usb_bulk_write()	(works fine, I get the data on the device)
> - usb_release_interface()
> **
> - usb_claim_interface()
> - usb_set_altinterface()
> 	- usb_bulk_read()		(works fine, I get the data from the device)
> - usb_release_interface()
> **
> - usb_claim_interface()
> - usb_set_altinterface()
> 	- usb_bulk_write()	(no failure (libusb), but I don't get any data on the device)
> - usb_release_interface()
> **
> - usb_claim_interface()
> - usb_set_altinterface()
> 	- usb_bulk_write()	(no failure (libusb), but I don't get any data on the device)
> 	- usb_bulk_read()		(fails, timeout error)
> 	- usb_bulk_write()	(works fine, I get the data on the device)
> 	- usb_bulk_read()		(fails, timeout error)
> 	- from now on all read/write are successful again
> - usb_release_interface()
> - usb_close()
> 
> ****************************
> 
> Is it not allowed to claim the interface again after release?
> I'm wondering why writing to the device succeeds, although I don't get any data on the device? I can write as many times as I want without getting an error from libusb. The device can buffer only one transfer.
> Strange is, that it starts working again after some subsequent write/reads.
> 
> Any hints are appreciated!
> Thanks, Andreas
> 
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