CODEWITHSUNDEEP
cimageusbraspberry-pilibusb
Mathew Wright
Mathew Wright

Reputation: 95

Why am I receiving 0 bytes of data from usb output from libusb bulk transfer?

I pulse a USB camera with a 5v pulse and it takes a picture. Pulsing the camera then sends a USB signal back to a raspberry pi. I'm writing a program to collect the images sent over USB. Below is my code for the function to begin taking input from the camera after it is triggered.

void opendevice()
{

libusb_device_handle* dev;
struct libusb_device_descriptor* desc;
int r;
int err;
int transfered;

   libusb_init(NULL);
   dev = libusb_open_device_with_vid_pid( NULL, 0x2a0b, 0x00f8);

      if (dev == NULL)
      {
          printf("device not found\n");
      }

      if(libusb_kernel_driver_active(dev, 0) == 1)
      {
           printf("Driver active\n");

       if(libusb_detach_kernel_driver(dev, 0) == 0)
        {

         printf("Kernel Driver Detached\n");
        }
      }

      libusb_set_configuration(dev,1);

     err = libusb_claim_interface(dev, 0);


    if(err != 0)
    {
       printf("cannot claim interface\n");
    }
     unsigned char usb_data[4];
     int size = sizeof(unsigned int) *1280 *960;
     unsigned *data;
     data = (unsigned int *)malloc(size);

    r = libusb_bulk_transfer(dev, LIBUSB_ENDPOINT_IN | 0x83, usb_data, sizeof(data), &transfered, 0); 

 if(r == 0)
  {
       printf("data has been transfered\n");
   } 
   else{ 
    printf("error code %d\n", r);
    printf("bytes transfered %d\n", transfered); 

  }

}

I locate the device detach check to see if the kernel is using it then if it is I detach it. After detaching it I claim the interface then wait for a transfer to happen inside of bulk transfer. However I never receive data from the transfer. Even when unplugging the camera from the usb port r returns value -1 and my transfer is of size 0. Can anyone tell me what I am missing here?

Let me know if you need any more information.

Upvotes: 3

Views: 1803

Answers (1)

Turbo J
Turbo J

Reputation: 7711

Your code has a buffer overflow:

     unsigned char usb_data[4]; // <---
     int size = sizeof(unsigned int) *1280 *960;
     unsigned *data;  // <-- not used!
     data = (unsigned int *)malloc(size);

    r = libusb_bulk_transfer(dev, LIBUSB_ENDPOINT_IN | 0x83, usb_data //<
    ,sizeof(data), &transfered, 0)

You probably wanted to use "data" as receiving buffer in the libusb_bulk_transfer() call, but you actually used usb_data which is only 4 bytes long.

Upvotes: 2

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