熟悉USB固件开发的高手进来看看，在线等

  void main(void)
{
   DWORD   i;
   WORD   offset;
   DWORD   DevDescrLen;
   DWORD   j=0;
   WORD   IntDescrAddr;
   WORD   ExtDescrAddr;

   // Initialize Global States
   Sleep = FALSE;               // Disable sleep mode
   Rwuen = FALSE;               // Disable remote wakeup
   Selfpwr = FALSE;            // Disable self powered
   GotSUD = FALSE;               // Clear "Got setup data" flag

   // Initialize user device
   TD_Init();

   // The following section of code is used to relocate the descriptor table.
   // Since the SUDPTRH and SUDPTRL are assigned the address of the descriptor
   // table, the descriptor table must be located in on-part memory.
   // The 4K demo tools locate all code sections in external memory.
   // The descriptor table is relocated by the frameworks ONLY if it is found
   // to be located in external memory.
  pDeviceDscr = (WORD)&DeviceDscr;
   pDeviceQualDscr = (WORD)&DeviceQualDscr;
   pHighSpeedConfigDscr = (WORD)&HighSpeedConfigDscr;
   pFullSpeedConfigDscr = (WORD)&FullSpeedConfigDscr;
   pStringDscr = (WORD)&StringDscr;

   if ((WORD)&DeviceDscr & 0xe000)
   {
      IntDescrAddr = INTERNAL_DSCR_ADDR;
      ExtDescrAddr = (WORD)&DeviceDscr;
      DevDescrLen = (WORD)&UserDscr - (WORD)&DeviceDscr + 2;
      for (i = 0; i < DevDescrLen; i++)
         *((BYTE xdata *)IntDescrAddr+i) = 0xCD;
      for (i = 0; i < DevDescrLen; i++)
         *((BYTE xdata *)IntDescrAddr+i) = *((BYTE xdata *)ExtDescrAddr+i);
      pDeviceDscr = IntDescrAddr;
      offset = (WORD)&DeviceDscr - INTERNAL_DSCR_ADDR;
      pDeviceQualDscr -= offset;
      pConfigDscr -= offset;
      pOtherConfigDscr -= offset;
      pHighSpeedConfigDscr -= offset;
      pFullSpeedConfigDscr -= offset;
      pStringDscr -= offset;
   }

   EZUSB_IRQ_ENABLE();            // Enable USB interrupt (INT2)
   EZUSB_ENABLE_RSMIRQ();            // Wake-up interrupt

   INTSETUP |= (bmAV2EN | bmAV4EN);     // Enable INT 2 & 4 autovectoring

   USBIE |= bmSUDAV | bmSUTOK | bmSUSP | bmURES | bmHSGRANT;   // Enable selected interrupts
   EA = 1;                  // Enable 8051 interrupts

#ifndef NO_RENUM
   // Renumerate if necessary.  Do this by checking the renum bit.  If it
   // is already set, there is no need to renumerate.  The renum bit will
   // already be set if this firmware was loaded from an eeprom.
   if(!(USBCS & bmRENUM))
   {
       EZUSB_Discon(TRUE);   // renumerate
   }
#endif

   // unconditionally re-connect.  If we loaded from eeprom we are
   // disconnected and need to connect.  If we just renumerated this
   // is not necessary but doesn't hurt anything
   USBCS &=~bmDISCON;

   CKCON = (CKCON&(~bmSTRETCH)) | FW_STRETCH_VALUE; // Set stretch to 0 (after renumeration)

   // clear the Sleep flag.
   Sleep = FALSE;

   // Task Dispatcher
   while(TRUE)               // Main Loop
   {
      if(GotSUD)            // Wait for SUDAV
      {
         SetupCommand();          // Implement setup command
           GotSUD = FALSE;            // Clear SUDAV flag
      }

      // Poll User Device
      // NOTE: Idle mode stops the processor clock.  There are only two
      // ways out of idle mode, the WAKEUP pin, and detection of the USB
      // resume state on the USB bus.  The timers will stop and the
      // processor will not wake up on any other interrupts.
      if (Sleep)
          {
          if(TD_Suspend())
              {
              Sleep = FALSE;            // Clear the "go to sleep" flag.  Do it here to prevent any race condition between wakeup and the next sleep.
              do
                  {
                    EZUSB_Susp();         // Place processor in idle mode.
                  }
                while(!Rwuen && EZUSB_EXTWAKEUP());
                // Must continue to go back into suspend if the host has disabled remote wakeup
                // *and* the wakeup was caused by the external wakeup pin.
                
             // 8051 activity will resume here due to USB bus or Wakeup# pin activity.
             EZUSB_Resume();   // If source is the Wakeup# pin, signal the host to Resume.      
             TD_Resume();
              }  
          }
      TD_Poll();
   }
}


其中DeviceDscr 这个变量是由谁赋值的
   if ((WORD)&DeviceDscr & 0xe000)他的意思是说：“DeviceDscr 这个变量的值与0xe000按位与，可不懂，为什么要这么做啊”。
请高手指点啊。

e000是外部数据ram的起始地址，这个条件是说如果descriptor table一开始被存储在外部存储器，那么将这部分数据转移到内部ram，这里要注意指针的变化，其实看懂了就很简单。