title: main.c:19: undefined reference to `usbInit' & undefined reference to `usbPoll'
body: <p>I faced with this error in building my project using v-usb library.followed is my code :</p>
  
  <pre><code>#include &lt;avr/io.h&gt;
  #include &lt;avr/interrupt.h&gt;
  #include &lt;avr/wdt.h&gt;
  
  #include "usbdrv.h"
  
  
  
  
  #include &lt;util/delay.h&gt;
  
  USB_PUBLIC uchar usbFunctionSetup(uchar data[8]) {
      return 0; // do nothing for now
  }
  
  int main() {
  
  uchar i;
  
  wdt_enable(WDTO_1S); // enable 1s watchdog timer
  
  usbInit();
  
  usbDeviceDisconnect(); // enforce re-enumeration
  for(i = 0; i&lt;250; i++) { // wait 500 ms
      wdt_reset(); // keep the watchdog happy
      _delay_ms(2);
  }
  usbDeviceConnect();
  
  sei(); // Enable interrupts after re-enumeration
  
  while(1) {
      wdt_reset(); // keep the watchdog happy
      usbPoll();
  }
  
  return 0;
  }
  </code></pre>
  
  <p>and this is relative part in usbdrv.h:</p>
  
  <pre><code> #ifndef USB_PUBLIC
  
   #define USB_PUBLIC
  
   #endif
  
  USB_PUBLIC void usbInit(void);
  
  USB_PUBLIC void usbPoll(void)
  </code></pre>
  
  <p>can someone help me?</p>