[libhid-discuss] libhid with python: help appreciated

[JamesPK]

Great - thanks for the feedback. Comments online below:

On 09/09/11 03:22, Charles Lepple wrote:
>> Hi,
>>
>> Apologies for what might be a basic libhid question.
>>
>> I'm running Ubuntu, and using libhid via Python to communicate with a 
>> HID device (and have used 'lsusb' to glean all the details of the 
>> device).
>>
>> I've started out with the example code here: 
>> http://anonscm.debian.org/viewvc/libhid/trunk/swig/test_libhid.py .I 
>> added  the vendor and product ID and the example code itself worked 
>> FINE.
>>
>> I then added some code to the example. From the 'snooping' on the 
>> communication with the device under Windows it needs a control 
>> message with an initialisation string to initialise the device, which 
>> I thought would be:
>
> Not to sound too nit-picky, but is it an actual USB control transfer, 
> or is it just a message that is being sent to the device?
>
> USB has the notion of Control endpoints (EP0 IN and OUT), and also 
> Interrupt endpoints. Not all devices have interrupt endpoints, but if 
> you post the output of 'lsusb -v' (run as root, preferably after 
> something like libhid has detached the kernel HID driver), we can see 
> which endpoints are available.

Good question - I'm not sure if its a control message required??? I 
expect it might just be a normal 'write'  message (as on double checking 
the on the windows output the 'request' filed was set as listed as 'set 
report' )

Ok - 'lsusb -v' is at base of post.

>> ret = hid_interrupt_write(hid, 0, INIT_SEQ, 8)
>> if ret != HID_RET_SUCCESS:
>>        log_error("hid_set_output_report", ret)
>>
>> But when I added the above spinet to the example and run it I get:
>> (ALL messages fine up to here)
>> ---------------------
>> NOTICE: hid_force_open(): successfully opened USB device 006/002[0].
>>  TRACE: hid_reset_parser(): resetting the HID parser for USB device 
>> 006/002[0]...
>>  TRACE: hid_dump_tree(): iterating the parse tree for USB device 
>> 006/002[0]...
>>  TRACE: hid_reset_parser(): resetting the HID parser for USB device 
>> 006/002[0]...
>>  TRACE: hid_interrupt_write(): writing interrupt report to device 
>> 006/002[0] ...
>> WARNING: hid_interrupt_write(): failed to perform interrupt write to 
>> device 006/002[0]: error submitting URB: No such file or directory
>> ---------------------
>
> Ah, I think I see what's going on: you passed endpoint 0 to 
> hid_interrupt_write() - it should be 1 or higher. Again, lsusb output 
> will pin this down.
>

Thanks.

James
-----------------------------------------------------------------
jamespk at hal:~/project/driver/hidapi$ sudo lsusb -v -d 0fde:ca01

Bus 006 Device 002: ID 0fde:ca01
Device Descriptor:
   bLength                18
   bDescriptorType         1
   bcdUSB               1.10
   bDeviceClass            0 (Defined at Interface level)
   bDeviceSubClass         0
   bDeviceProtocol         0
   bMaxPacketSize0         8
   idVendor           0x0fde
   idProduct          0xca01
   bcdDevice            3.02
   iManufacturer           0
   iProduct                1 Universal Bridge
   iSerial                 0
   bNumConfigurations      1
   Configuration Descriptor:
     bLength                 9
     bDescriptorType         2
     wTotalLength           34
     bNumInterfaces          1
     bConfigurationValue     1
     iConfiguration          0
     bmAttributes         0x80
       (Bus Powered)
     MaxPower              100mA
     Interface Descriptor:
       bLength                 9
       bDescriptorType         4
       bInterfaceNumber        0
       bAlternateSetting       0
       bNumEndpoints           1
       bInterfaceClass         3 Human Interface Device
       bInterfaceSubClass      0 No Subclass
       bInterfaceProtocol      0 None
       iInterface              0
         HID Device Descriptor:
           bLength                 9
           bDescriptorType        33
           bcdHID               1.10
           bCountryCode            0 Not supported
           bNumDescriptors         1
           bDescriptorType        34 Report
           wDescriptorLength      34
           Report Descriptor: (length is 34)
             Item(Global): Usage Page, data= [ 0x00 0xff ] 65280
                             (null)
             Item(Local ): Usage, data= [ 0x01 ] 1
                             (null)
             Item(Main  ): Collection, data= [ 0x01 ] 1
                             Application
             Item(Local ): Usage, data= [ 0x01 ] 1
                             (null)
             Item(Global): Logical Minimum, data= [ 0x00 ] 0
             Item(Global): Logical Maximum, data= [ 0xff 0x00 ] 255
             Item(Global): Report Size, data= [ 0x08 ] 8
             Item(Global): Report Count, data= [ 0x08 ] 8
             Item(Main  ): Input, data= [ 0x00 ] 0
                             Data Array Absolute No_Wrap Linear
                             Preferred_State No_Null_Position 
Non_Volatile Bitfield
             Item(Local ): Usage, data= [ 0x02 ] 2
                             (null)
             Item(Global): Logical Minimum, data= [ 0x00 ] 0
             Item(Global): Logical Maximum, data= [ 0xff 0x00 ] 255
             Item(Global): Report Size, data= [ 0x08 ] 8
             Item(Global): Report Count, data= [ 0x08 ] 8
             Item(Main  ): Output, data= [ 0x02 ] 2
                             Data Variable Absolute No_Wrap Linear
                             Preferred_State No_Null_Position 
Non_Volatile Bitfield
             Item(Main  ): End Collection, data=none
       Endpoint Descriptor:
         bLength                 7
         bDescriptorType         5
         bEndpointAddress     0x81  EP 1 IN
         bmAttributes            3
           Transfer Type            Interrupt
           Synch Type               None
           Usage Type               Data
         wMaxPacketSize     0x0008  1x 8 bytes
         bInterval               1
Device Status:     0x0000
   (Bus Powered)
--------------------------------------------