SelectMIO(BOOL MIO)的作用?

exe中:BOOL SelectMIO(BOOL MIO)
{
if (hPDC1000 == NULL)
{
return FALSE;
}

ULONG BytesReturned,retlength;
unsigned char Buffer,OutBuf;

if (MIO)
Buffer = 0x00; //选择的是Memory.
else
Buffer = 0x01; //选择的是IO.

if (!DeviceIoControl(hPDC1000, IOCTL_PDC1000_SELECT_8155MIO, &Buffer, 1,
NULL, 0, &BytesReturned, NULL))


sys中:


case IOCTL_PDC1000_SELECT_8155MIO:
//通过PCI9052的User0，进行选择
unsigned char Selected;
ULONG Address;
ULONG TempData;
Address = (ULONG)((PDEVICE_EXTENSION)pdx)->MemBase;
RtlCopyMemory(&Selected, pIrp->AssociatedIrp.SystemBuffer, 1);

TempData = READ_REGISTER_ULONG((ULONG *)(Address + 0x50));
if (Selected == 0x00)
{
TempData &= 0xfffffffa;
}
else if(Selected == 0x01)
{
TempData |= 0x00000006;
}

WRITE_REGISTER_ULONG((ULONG *)(Address + 0x50), TempData);

ReturnedValue = 0;
break;


SelectMIO(BOOL MIO)的作用是什么呀?看了半天没看懂.

忘了说一句:是PDC1000的驱动

sorry,硬件不太懂,我只做驱动,大概给我说一下功能就可以了.
3x.