[libusb] Diagnosing Input/output error on first read from a device

[Michael B. <mic...@gm...>]

Hi there,

I'm trying to read input from a USB device.

I'm on Linux.  I connected a USB device.  I added it to udev rules to gain
permissions.  I got resource busy on set_configuration, so I did
'usb-devices' and found Driver= lines that correspond to the device and
rmmod'd them.

I probe for and unload any attached kernel driver in code.

Now I can successfully connect to the device, but doing an interrupting
receive (the first one), with any number of bytes, returns an Input/output
error.

As per usb-devices output, the device that's having the IO error is:

T:  Bus=01 Lev=02 Prnt=02 Port=00 Cnt=01 Dev#=  8 Spd=480 MxCh= 0
D:  Ver= 2.00 Cls=ef(misc ) Sub=02 Prot=01 MxPS=64 #Cfgs=  1
P:  Vendor=17cc ProdID=1310 Rev=00.46
S:  Manufacturer=Native Instruments
S:  Product=Traktor Kontrol S4 MK2
S:  SerialNumber=5C9367B8
C:  #Ifs= 7 Cfg#= 1 Atr=80 MxPwr=480mA
I:  If#= 0 Alt= 0 #EPs= 0 Cls=01(audio) Sub=01 Prot=20 Driver=(none)
I:  If#= 1 Alt= 0 #EPs= 0 Cls=01(audio) Sub=02 Prot=20 Driver=(none)
I:  If#= 2 Alt= 0 #EPs= 0 Cls=01(audio) Sub=02 Prot=20 Driver=(none)
I:  If#= 3 Alt= 0 #EPs= 2 Cls=01(audio) Sub=03 Prot=00 Driver=(none)
I:  If#= 4 Alt= 0 #EPs= 2 Cls=03(HID  ) Sub=00 Prot=00 Driver=(none)
I:  If#= 5 Alt= 0 #EPs= 0 Cls=fe(app. ) Sub=01 Prot=01 Driver=(none)
I:  If#= 6 Alt= 0 #EPs= 3 Cls=ff(vend.) Sub=f0 Prot=00 Driver=(none)

This is puzzling because a similar device, from the same company, "works
fine" with the same connect/read code:

T:  Bus=01 Lev=02 Prnt=02 Port=00 Cnt=01 Dev#=  9 Spd=480 MxCh= 0
D:  Ver= 2.00 Cls=00(>ifc ) Sub=00 Prot=00 MxPS=64 #Cfgs=  1
P:  Vendor=17cc ProdID=1120 Rev=00.0b
S:  Manufacturer=Native Instruments
S:  Product=Traktor Kontrol F1
S:  SerialNumber=D67CCB9F
C:  #Ifs= 2 Cfg#= 1 Atr=80 MxPwr=480mA
I:  If#= 0 Alt= 0 #EPs= 2 Cls=03(HID  ) Sub=00 Prot=00 Driver=(none)
I:  If#= 1 Alt= 0 #EPs= 0 Cls=fe(app. ) Sub=01 Prot=01 Driver=(none)

The only difference in the code paths is that I select interface=0 on the
latter and interface=4 on the former.

libusb_set_configuration(handle, 1);
libusb_claim_interface(handle, interface);

Am I using the wrong kind of read?  Did I forget to set a parameter?  How
would I know from the device output above?

Thanks for any light that can be shed on this!

-- 
Michael Bacarella