VxWorks下关于PCI驱动部分的一些程序

VxWorks下关于PCI驱动部分的一些程序，有几个地方我不是很明白。请指点！
其实也不算是驱动部分了，请看看吧
UINT32 address;
//----------------------------------------------------------
// check for PCI device
//----------------------------------------------------------
    if (pciFindDevice (fVendorId, fDeviceId, getIndex(),
                   &busNumber, &deviceNumber, &functionNumber) != OK)
    {
        fDiscoveryOk = false;
        return;
    }
    //------------------------------------------------------
    // determine device interrupt
    //------------------------------------------------------
    unsigned int intLine;
    pciConfigInLong(
        busNumber, deviceNumber, functionNumber, PCI_INT_LINE_OFFSET, &intLine);

    // Set the IRQ number for interrupts from the PCI device.
    intLine &= 0x000000ff;
    fIrq = (unsigned long)intLine;
    //------------------------------------------------------
    // determine device I/O and memory base addresses
    // NOTE:  some devices define offset 0 to be memory base,
    //        while others define it as the I/O base.
    //------------------------------------------------------
    pciConfigInLong(
        busNumber, deviceNumber, functionNumber, PCI_BAR_0_OFFSET, &address);
    cout << \"pciConfigInLong method returned address \" << address << endl;
    //------------------------------------------------------
    // actual start address
    //------------------------------------------------------
    address &= 0xfffffff0; // Clear out the status bits in the lower nibble

    address |= 0x20000000; // Endianness
        // Set BAR0 for the 3212 chip so we can access configuration registers.
        fBar[0] = address;
        //----------------------------------------------------------------------
        // Get base address for MAC address space (PCI base address for local
        // space 0
        //----------------------------------------------------------------------
        pciConfigInLong(
            busNumber, deviceNumber, functionNumber, PCI_BAR_1_OFFSET, &address);
    
        address &= 0xfffffff0; // Clear out the status bits in the lower nibble
    
        address |= 0x20000000; // Endianness
        // Set BAR1 for the 3212 chip so we can access configuration registers.
        fBar[1] = address;
我觉得奇怪，为什么BAR0同时是memory和I/O地址呢？
address |= 0x20000000; // Endianness还有这一句是指置状态位吗？