[libusb] Example code for libusb novice users

[<jfp...@fa...>]

Greetings,
After several attempts at using the libusb functions, I am now able to
communicate with the hardware
I'm developing.  A big 'thank you' to all the libusb developers.

I'm offering my basic code as a help to other libusb beginning users,
particularly to those who, like myself, may not be
'professionally fluent' in C.  In the source files in the installed
examples/ directory, there's quite a jump in complexity from listdevs.c
to, for instance, dpfp.c.  My code fits in between, and if someone
would choose to include it in the examples/ directory, perhaps with
some editing, that is OK with me.

BTW, I did find the example files at libusb.org, but their existence
could be made more obvious.  Just a suggestion.

So here's my code.  Comments welcomed.  Thanks again,
John Parsons
(If there's another preferred method to post code, please let me know.)

// filename: hellodev.c
// Minimal routine to transfer data to/from a simple USB device
// using libusb-1.0.9 functions.
// This example uses interrupt data transfers.
// Developed and run on an Ubuntu 12.0.4 system, with libusb-1.0
// and libusb-1.0-dev packages installed via Synaptic Package
// Manager.

// Compile command used:
// gcc hellodev.c -o hellodev $(pkg-config --cflags --libs libusb-1.0)

// Run command:  sudo ./hellodev
//  ** Note **
//  Must be root in order to successfully open a device.

#include <stdio.h>
#include <sys/types.h>
#include <libusb.h>

// Adjust the following values to match the actual device in use:
#define VID_MINE   0x265f
#define PID_MINE   0xfcb2
#define INTERFACE_NUM   0
#define EPNUM_IN   0x81   // IN endpoint number
#define EPNUM_OUT  0x01   // OUT endpoint number

#define DOUT_LENGTH 1    // number of bytes of OUT data
#define DIN_LENGTH  16   // number of bytes of IN data

int main (void)
{
   libusb_device **list;
   libusb_device_handle *devh = NULL;
   ssize_t dcount, i;
   int r, transferred;
   uint8_t dout[DOUT_LENGTH], din[DIN_LENGTH];

   dout[0] = 0x52;   // example data out (to be sent to device)

   r = libusb_init(NULL);   // the NULL parameter causes a
                            // default context to be created
   if(0 == r) {
      printf("Success libusb_init\n");

      //Get list of connected devices and how many there are.
      dcount = libusb_get_device_list(NULL, &list);   

      printf("Got device list, dcount = %d\n", dcount);

      if(0 < dcount) {  // If 1 or more devices were found...
         devh = libusb_open_device_with_vid_pid(NULL, 0x265f, 0xfcb2);
         if (NULL != devh) {
            printf("Found my device\n");
            r = libusb_claim_interface(devh, INTERFACE_NUM);
            if(0 == r) {
               printf("Successfully claimed interface...\n");

               // Send data to device
               r = libusb_interrupt_transfer(devh, EPNUM_OUT, dout,
                    DOUT_LENGTH, &transferred, 500);
               if(0 == r) {
                  printf("Data sent successfully, transferred = %d\n",
                          transferred);
               }
               else {
                  printf("Send data failed r = %d, transferred = %d\n",
                           r, transferred);
               }

               // Request data from device...
               // This example device requires that a 'send data'
               command
               // byte (0x57) be sent to it, then it will send back 16
               bytes.
               dout[0] = 0x57;
               r = libusb_interrupt_transfer(devh, EPNUM_OUT, dout,
                    DOUT_LENGTH, &transferred, 500);
               if(0 == r) {
                  printf("'send data' cmd OK, transferred = %d\n",
                  transferred);
               }
               else {
                  printf("'send data' cmd failed r = %d, transferred =
                  %d\n",
                          r, transferred);
               }

               // Now actually get the data...
               r = libusb_interrupt_transfer(devh, EPNUM_IN, din,
               DIN_LENGTH,
                    &transferred, 500);
               if(0 == r) {
                  printf("Data received OK, transferred = %d\n",
                  transferred);
               }
               else {
                  printf("Data request failed r = %d, transferred =
                  %d\n",
                           r, transferred);
               }

               // Release interface when transfers are complete...
               r = libusb_release_interface(devh, INTERFACE_NUM);
               if(0 == r) {
                  printf("OK, libusb_release_interface returned 0\n");
               }
               else {
                  printf("Error, libusb_release_interface returned
                  %d\n", r);
               }
            }
            else {
               printf("Sorry, unable to claim interface, r = %d\n", r);
            }
            libusb_close(devh);   // must close device before exiting
         }
         else {
            printf("Sorry, libusb_open_dev... returned NULL\n");
         }
         libusb_free_device_list(list, 1);   // must free devices before
         exiting
      }
      else {
         printf("Sorry, unable to get device list, dcount = %d\n",
         dcount);
      }
      libusb_exit(NULL);      // 'de-initialize' the default context
   }
   else {  // libusb_init error
      printf("Sorry, libusb_init returned r = %d\n", r);
   }

   // Print the data that was sent by the device...
   printf("Received bytes:\n");
   for(i = 0; i < DIN_LENGTH; i++) {
      printf(" %02x", din[i]);
   }
   printf("\n  Ciao.\n");
} // main