怎么无法申请DMA缓冲区？

小弟正在做一块高速数据采集卡的论文，用的是ISA接口，DMA传输。我用VTOOLSD作了个驱动程序，但每次在装载时，当运行到保留一块DMA缓冲区（即调用VMDABuffer::reserve(...)时），系统就锁死不动。请问这是怎么回事，该如何解决。谢谢！
附程序如下：

// WAH002.h - include file for VxD WAH002

#include <vtoolscp.h>

#define DEVICE_CLASS Wah002Device
#define WAH002_DeviceID UNDEFINED_DEVICE_ID
#define WAH002_Init_Order UNDEFINED_INIT_ORDER
#define WAH002_Major 1
#define WAH002_Minor 0

#define MY_IRQ 10
#define MY_DMA 6


class MyHwInt : public VHardwareInt
{
public:
MyHwInt() : VHardwareInt(MY_IRQ,0,0,0){};
virtual VOID OnHardwareInt(VMHANDLE);
};

  

class Wah002Device : public VDevice
{
public:
virtual BOOL OnSysDynamicDeviceInit();
virtual BOOL OnSysDynamicDeviceExit();
virtual DWORD OnW32DeviceIoControl(PIOCTLPARAMS pDIOCParams);
};

class MyDMAChannel : public VDMAChannel    // VDMAChannel类定义
{
public:
MyDMAChannel() : VDMAChannel(6) {}
virtual VOID handler(VMHANDLE hVM);
};
class MyBuffer : public VDMABuffer      // VDMABuffer类定义
{
public:
MyBuffer(PVOID regionAddress, DWORD regionSize) : VDMABuffer(regionAddress, regionSize){}
};


// WAH002.cpp - main module for VxD WAH002

#define DEVICE_MAIN
#include \"wah002.h\"
Declare_Virtual_Device(WAH002)
#undef DEVICE_MAIN

#include \"apcx.h\"

MyHwInt* pMyIRQ;
PVOID CallBackApc = 0;
THREADHANDLE TheThread = 0;
MyDMAChannel* pMyDMA;
MyBuffer* pMyBUF;
DWORD errCode;
PVOID region;
DWORD size;
DWORD MAX_TRANSFER_PAGES=4096;
DWORD MAX_PHYS_ADDR=0x1000000;


VOID MyHwInt::OnHardwareInt(VMHANDLE hVM)
{
    _outp(0x304,0x00);
    sendPhysicalEOI();
    VWIN32_QueueUserApc(CallBackApc, NULL, TheThread);
}



VOID MyDMAChannel::handler(VMHANDLE hVM)   // 重载handler成员函数
{
  VDMAChannel::handler(hVM); // let VDMAD do all the work
}

BOOL Wah002Device::OnSysDynamicDeviceInit()
{
pMyIRQ = new MyHwInt();
if ((pMyIRQ==NULL) || !pMyIRQ->hook()) return FALSE;
pMyDMA = new MyDMAChannel();
if ((pMyDMA==NULL) || !pMyDMA->hook()) return FALSE;
VDMABuffer::reserve(MAX_TRANSFER_PAGES,
                             (PVOID)MAX_PHYS_ADDR);
return TRUE;
}

BOOL Wah002Device::OnSysDynamicDeviceExit()
{
if (pMyDMA) delete pMyDMA;
if (pMyIRQ) delete pMyIRQ;
return TRUE;
}

DWORD Wah002Device::OnW32DeviceIoControl(PIOCTLPARAMS pDIOCParams)
{
DWORD status;
switch (pDIOCParams->dioc_IOCtlCode)
{
case DIOC_OPEN:
_outp(0x303,0x00);
status = 0;
break;
case DIOC_CLOSEHANDLE:
if (pMyBUF) delete pMyBUF;
status = 0;
break;
case REGISTER:
CallBackApc = pDIOCParams->dioc_InBuf;
TheThread = Get_Cur_Thread_Handle();
status = 0;
break;
case DMASET:    //设置DMA通道
region = pDIOCParams->dioc_InBuf;
size= pDIOCParams->dioc_cbInBuf;
pMyBUF = new MyBuffer(NULL,size);
if (pMyBUF->m_createError == 0)
{
pMyDMA->setRegion(pMyBUF, FALSE, NULL, size, pMyBUF->m_physAddress);
pMyDMA->setPhysicalState(Get_Cur_VM_Handle(),DMA_type_write | DMA_block_mode);
pMyDMA->physicalUnmask(Get_Cur_VM_Handle(),FALSE);
pMyIRQ->physicalUnmask();
status = 0;
}
else status = -1;
break;
case READ:    //把buffer的数据拷贝到region
pMyBUF->copyFrom(region, size, 0, errCode);
//重新设置DMA缓冲区
pMyDMA->setRegion(pMyBUF, FALSE, NULL, size, pMyBUF->m_physAddress);
pMyDMA->setPhysicalState(Get_Cur_VM_Handle(),DMA_type_write|DMA_single_mode);
pMyDMA->physicalUnmask(Get_Cur_VM_Handle(),FALSE);
status = 0;
break;
default:
status = -1;
}
return status;
}

//apcx.h

#define REGISTER  CTL_CODE(FILE_DEVICE_UNKNOWN, 1, METHOD_NEITHER, FILE_ANY_ACCESS)
#define DMASET    CTL_CODE(FILE_DEVICE_UNKNOWN, 2, METHOD_NEITHER, FILE_ANY_ACCESS)
#define READ      CTL_CODE(FILE_DEVICE_UNKNOWN, 3, METHOD_NEITHER, FILE_ANY_ACCESS)

不需要VDMABuffer::reserve，直接用VDMABuffer即可。