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精簡ISA總線是英創工控主板的特色之一，我們基于ISA總線推出了多串口、多網口、多CAN 接口等擴展模塊，我們的很多用戶也基于ISA總線設計了自己的專有擴展單元并取得了成功。為了充分發揮ISA總線的性能，對于ISA總線的訪問，我們除了提供最基本的設備驅動API操作函數外，還先后增加了ISA總線的塊讀寫操作方法和ISA總線的DMA操作方法。當ISA總線以DMA方式進行數據傳輸時，在最大限度的利用ISA總線帶寬的同時，又減少了ISA操作占用CPU的時間，所以利用DMA是進行批量數據傳輸時的首選方式。

在實際的應用中，除了成批量的數據訪問外，也可能會存在對外設進行頻繁的字或字節訪問。英創主板的ISA總線周期通常在200ns左右，而應用程序調用一次設備驅動程序API(WriteFile，ReadFile)花費的時間卻需要數微秒的時間，這顯然大大降低了對外設單字（或單字節）的訪問效率。為了解決這一問題，我們利用了WinCE的虛擬地址映射技術，在ISA驅動程序中實現了在使用ISA的應用進程地址空間內分配一段虛擬地址空間，并將其與ISA接口的物理地址空間進行了綁定。簡單來講就是實現了在WinCE應用程序中可以直接訪問ISA總線的外設地址空間，從使用的角度看，我們實現了以下5個函數。ISAMmMap用于獲得ISA總線的基地址，其余4個函數分別為字讀/寫和字節讀/寫操作函數。

HANDLE ISAMmMap(HANDLE hISA); // 映射ISA總線物理地址空間
BYTE ISARead8(HANDLE hMmMap, DWORD dwPortOffset); // 讀單字節
void ISAWrite8(HANDLE hMmMap, DWORD dwPortOffset, BYTE ucValue); // 寫單字節
WORD ISARead16(HANDLE hMmMap, DWORD dwPortOffset); // 讀單字
void ISAWrite16(HANDLE hMmMap, DWORD dwPortOffset, WORD wValue); // 寫單字

下面是上述5個函數實現的源代碼，在ISAMmMap函數中調用DeviceIoControl，通過IOCTL_VIRTUAL_COPY_EX命令獲取ISA總線的基地址。

// Function: Get the base address of ISA Port
// Input: hISA: Handle of ISA1:
// Return: Base address of the ISA Port
HANDLE ISAMmMap(HANDLE hISA)
{
DWORD dwMemBase;
if(DeviceIoControl(hISA, //打開“ISA1:”返回的Handler
IOCTL_VIRTUAL_COPY_EX, // IOCTL命令碼
NULL,0, // 不使用輸入參數
&dwMemBase, sizeof(DWORD), // 得到ISA基地址
NULL, NULL))
return (HANDLE)dwMemBase;
return NULL;
}
// Function: read a byte from a port on ISA bus
// Input: hMmMap: Base address of the ISA Port
// dwPortOffset = 0, 1, .. 255, address of port on ISA
// Return: the byte data read
BYTE ISARead8(HANDLE hMmMap, DWORD dwPortOffset)
{
WORD *pPortAddr;
WORD wValue;
dwPortOffset &= 0xff;
dwPortOffset <<= 1;?????????????? // D[0..7] <=> A[1..8] in AD-muxed mode
pPortAddr = (WORD*)((DWORD)hMmMap + dwPortOffset);
wValue = *pPortAddr;
return (BYTE)wValue;
}
// Function: write a byte to a port on ISA bus
// Input: hMmMap: Base address of the ISA Port//
// dwPortOffset = 0, 1, .. 255, address of port on ISA
// ucValue = the byte data to be written
void ISAWrite8(HANDLE hMmMap, DWORD dwPortOffset, BYTE ucValue)
{
WORD *pPortAddr;
dwPortOffset &= 0xff;
dwPortOffset <<= 1;?????????????? // D[0..7] <=> A[1..8] in AD-muxed mode
pPortAddr = (WORD*)((DWORD)hMmMap + dwPortOffset);
*pPortAddr = (WORD)ucValue;
}
// Function: read a word from a port on ISA bus
// Input: hMmMap: Base address of the ISA Port
// dwPortOffset = 0, 2, 4, .. 254, address of port on ISA
// Return: the word data read
WORD ISARead16(HANDLE hMmMap, DWORD dwPortOffset)
{
DWORD *pPortAddr;
DWORD dwValue;
dwPortOffset &= 0xFE; // 2-byte alignment
dwPortOffset <<= 1;?????????????? // D[0..7] <=> A[1..8] in AD-muxed mode
pPortAddr = (DWORD*)((DWORD)hMmMap + dwPortOffset);
dwValue = *pPortAddr;
// the high-byte of data is at value[23..16]
return (WORD)(((dwValue >> 8) & 0xFF00) | (dwValue & 0xFF));
}
// Function: write a word to a port on ISA bus
// Input: hMmMap: Base address of the ISA Port
// dwPortOffset = 0, 2, 4, .. 254, address of port on ISA
// wValue = the word data to be written
void ISAWrite16(HANDLE hMmMap, DWORD dwPortOffset, WORD wValue)
{
DWORD *pPortAddr;
DWORD dwValue;
dwPortOffset &= 0xFE; // 2-byte alignment
dwPortOffset <<= 1;?????????????? // D[0..7] <=> A[1..8] in AD-muxed mode
pPortAddr = (DWORD*)((DWORD)hMmMap + dwPortOffset);
dwValue = wValue;
// dispatch high-byte of data to value[23..16]
*pPortAddr = ((dwValue << 8) & 0x00ff0000) | (dwValue & 0x000000ff);
}

我們在ESM3352上，分別測試了利用地址映射方法直接訪問ISA外設地址和調用設備驅動API函數讀寫ISA地址，測得的結果是當進行字(WORD)讀寫時，應用程序直接訪問ISA外設地址比調用設備驅動API函數快10倍以上，當時行字節(BYTE)讀寫時，應用程序直接訪問ISA外設地址比調用設備驅動API函數快15倍以上。

下面是測試程序源代碼：

int _tmain(int argc, _TCHAR* argv[])
{
HANDLE hISA, hMmMap;
BYTE ucValue;
WORD wValue;
DWORD dwStartTick, dwEndTick, i, k, cnt=2000;
hISA = CreateFile(_T("ISA1:"), // name of device
GENERIC_READ|GENERIC_WRITE, // desired access
FILE_SHARE_READ|FILE_SHARE_WRITE, // sharing mode
NULL, // security attributes (ignored)
OPEN_EXISTING, // creation disposition
FILE_FLAG_RANDOM_ACCESS, // flags/attributes
NULL);
hMmMap = ISAMmMap(hISA);
if(hMmMap == NULL)
return -1;
printf("ISA read/write speed test\r\n");
printf("Memory Map VS Device Driver API\r\n");
dwStartTick = GetTickCount();
for(i=0; i for(k=0; k<256; k++)
{
ISAWrite8(hMmMap, k, 0x55);
ucValue = ISARead8(hMmMap, k);
}
dwEndTick = GetTickCount();
printf("1. Memory map BYTE read/write %d KBytes, Take time:%d ms\r\n", 256 * 2 *cnt / 1024, dwEndTick - dwStartTick);
dwStartTick = GetTickCount();
for(i=0; i for(k=0; k<256; k++)
{
ISA_WriteUchar( hISA, k, 0x55 );
ISA_ReadUchar( hISA, k, &ucValue );
}
dwEndTick = GetTickCount();
printf("2. Device driver API BYTE read/write %d KBytes, Take time:%d ms\r\n", 256 * 2 * cnt/ 1024, dwEndTick - dwStartTick);
cnt /= 2;
dwStartTick = GetTickCount();
for(i=0; i for(k=0; k<256; k++)
{
ISAWrite16(hMmMap, k, 0x55AA);
wValue = ISARead16(hMmMap, k);
}
dwEndTick = GetTickCount();
printf("3. Memory map WORD read/write %d KBytes, Take time:%d ms\r\n", 256 * 4 * cnt / 1024, dwEndTick - dwStartTick);
dwStartTick = GetTickCount();
for(i=0; i for(k=0; k<256; k++)
{
ISA_WriteWord( hISA, k, 0x55AA );
ISA_ReadWord( hISA, k, &wValue );
}
dwEndTick = GetTickCount();
printf("4. Device driver API WORD read/write %d KBytes, Take time:%d ms\r\n", 256 * 4 * cnt / 1024, dwEndTick - dwStartTick);
CloseHandle(hISA);
return 0;
}

下面是在ESM3352上兩種訪問方式的測試結果：