[libusb] Data in the USB packets

[Stefano M. <s....@am...>]

Hi all,

I'm writing a console program to communicate with a USB printer and I need
to use libusb functions on Linaro Linux.
The device is correctly found by VID and PID,:

  Endpoint Descriptor:

    bLength                 7

    bDescriptorType         5

    bEndpointAddress     0x81  EP 1 IN

    bmAttributes            2

      Transfer Type            Bulk

      Synch Type               None

      Usage Type               Data

    wMaxPacketSize     0x0040  1x 64 bytes

    bInterval               0

  Endpoint Descriptor:

    bLength                 7

    bDescriptorType         5

    bEndpointAddress     0x02  EP 2 OUT

    bmAttributes            2

      Transfer Type            Bulk

      Synch Type               None

      Usage Type               Data

    wMaxPacketSize     0x0040  1x 64 bytes

    bInterval               0

 

The cmmands are simply 3-bytes array and I sent them by the bulk function:

dump( cmdPrinter, nCmdSize, "[usbxsfer] OUT:");

    

ret = libusb_bulk_transfer( devHandle, EP_OUT, 

            (unsigned char*)&cmdPrinter, nCmdSize, &wrote, timeout);

LOG4("[usbxsfer] OUT[x%02X] ret: %d - wrote: %d - pcksize=%d\n", 

    EP_OUT, ret, wrote, nCmdSize);

 

The result is good (wrote=3) and 3 bytes are sent:

[2022-08-26 18:11:55] [usbxsfer] devHandle: 0x55a8dbdac0, nCmdSize: 3

[2022-08-26 18:11:55] [usbxsfer] OUT: [3] 1D E0 0F

[2022-08-26 18:11:55] [usbxsfer] OUT[x02] ret: 0 - wrote: 3 - pcksize=3

 

After that, I try to read the reply by:

int toRead = 10;

ret = libusb_bulk_transfer(devHandle, EP_IN, (unsigned char*)bufferRx+offs,
toRead, &xferred, timeout);

LOG2("[usbxsfer] IN ret: %d - xferred: %d\n", ret, xferred);

 

The device does not execute the command (eject some labels) and does not
reply (error -7 = timeout (3 seconds)).

I installed tshark to sniff the bytes on the cable and sending '1D E0 0F'
bytes I see:

Frame 3: 67 bytes on wire (536 bits), 67 bytes captured (536 bits) on
interface 0

    Interface id: 0 (usbmon0)

        Interface name: usbmon0

    Encapsulation type: USB packets with Linux header and padding (115)

    Arrival Time: Aug 26, 2022 18:11:55.083144000 CEST

    [Time shift for this packet: 0.000000000 seconds]

    Epoch Time: 1661530315.083144000 seconds

    [Time delta from previous captured frame: 0.001053000 seconds]

    [Time delta from previous displayed frame: 0.001053000 seconds]

    [Time since reference or first frame: 0.001211000 seconds]

    Frame Number: 3

    Frame Length: 67 bytes (536 bits)

    Capture Length: 67 bytes (536 bits)

    [Frame is marked: False]

    [Frame is ignored: False]

    [Protocols in frame: usb]

USB URB

    [Source: host]

    [Destination: 5.6.2]

    URB id: 0xffffffc0774cfe40

    URB type: URB_SUBMIT ('S')

    URB transfer type: URB_BULK (0x03)

    Endpoint: 0x02, Direction: OUT

        0... .... = Direction: OUT (0)

        .... 0010 = Endpoint number: 2

    Device: 6

    URB bus id: 5

    Device setup request: not relevant ('-')

    Data: present (0)

    URB sec: 1661530315

    URB usec: 83144

    URB status: Operation now in progress (-EINPROGRESS) (-115)

    URB length [bytes]: 3

    Data length [bytes]: 3

    [bInterfaceClass: Unknown (0xffff)]

    Unused Setup Header

    Interval: 0

    Start frame: 0

    Copy of Transfer Flags: 0x00000000

    Number of ISO descriptors: 0

Leftover Capture Data: d8abcb

 

0000  40 fe 4c 77 c0 ff ff ff 53 03 02 06 05 00 2d 00   @.Lw....S.....-.

0010  cb f0 08 63 00 00 00 00 c8 44 01 00 8d ff ff ff   ...c.....D......

0020  03 00 00 00 03 00 00 00 00 00 00 00 00 00 00 00   ................

0030  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00   ................

0040  d8 ab cb                                          ...

 

This should be the packet sent to the device but I don't see my bytes! Maybe
this is the reason why the command is not executed and have no reply.

Any idea?

 

 

Ing. Stefano Mora

 



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