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精簡(jiǎn)ISA總線(xiàn)是英創(chuàng)工控主板的特色之一，我們基于ISA總線(xiàn)推出了多串口、多網(wǎng)口、多CAN 接口等擴(kuò)展模塊，我們的很多用戶(hù)也基于ISA總線(xiàn)設(shè)計(jì)了自己的專(zhuān)有擴(kuò)展單元并取得了成功。為了充分發(fā)揮ISA總線(xiàn)的性能，對(duì)于ISA總線(xiàn)的訪(fǎng)問(wèn)，我們除了提供最基本的設(shè)備驅(qū)動(dòng)API操作函數(shù)外，還先后增加了ISA總線(xiàn)的塊讀寫(xiě)操作方法和ISA總線(xiàn)的DMA操作方法。當(dāng)ISA總線(xiàn)以DMA方式進(jìn)行數(shù)據(jù)傳輸時(shí)，在最大限度的利用ISA總線(xiàn)帶寬的同時(shí)，又減少了ISA操作占用CPU的時(shí)間，所以利用DMA是進(jìn)行批量數(shù)據(jù)傳輸時(shí)的首選方式。

在實(shí)際的應(yīng)用中，除了成批量的數(shù)據(jù)訪(fǎng)問(wèn)外，也可能會(huì)存在對(duì)外設(shè)進(jìn)行頻繁的字或字節(jié)訪(fǎng)問(wèn)。英創(chuàng)主板的ISA總線(xiàn)周期通常在200ns左右，而應(yīng)用程序調(diào)用一次設(shè)備驅(qū)動(dòng)程序API(WriteFile，ReadFile)花費(fèi)的時(shí)間卻需要數(shù)微秒的時(shí)間，這顯然大大降低了對(duì)外設(shè)單字（或單字節(jié)）的訪(fǎng)問(wèn)效率。為了解決這一問(wèn)題，我們利用了WinCE的虛擬地址映射技術(shù)，在ISA驅(qū)動(dòng)程序中實(shí)現(xiàn)了在使用ISA的應(yīng)用進(jìn)程地址空間內(nèi)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(jìn)行了綁定。簡(jiǎn)單來(lái)講就是實(shí)現(xiàn)了在WinCE應(yīng)用程序中可以直接訪(fǎng)問(wèn)ISA總線(xiàn)的外設(shè)地址空間，從使用的角度看，我們實(shí)現(xiàn)了以下5個(gè)函數(shù)。ISAMmMap用于獲得ISA總線(xiàn)的基地址，其余4個(gè)函數(shù)分別為字讀/寫(xiě)和字節(jié)讀/寫(xiě)操作函數(shù)。

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

下面是上述5個(gè)函數(shù)實(shí)現(xiàn)的源代碼，在ISAMmMap函數(shù)中調(diào)用DeviceIoControl，通過(guò)IOCTL_VIRTUAL_COPY_EX命令獲取ISA總線(xiàn)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(kāi)“ISA1:”返回的Handler
IOCTL_VIRTUAL_COPY_EX, // IOCTL命令碼
NULL,0, // 不使用輸入?yún)?shù)
&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?cè)贓SM3352上，分別測(cè)試了利用地址映射方法直接訪(fǎng)問(wèn)ISA外設(shè)地址和調(diào)用設(shè)備驅(qū)動(dòng)API函數(shù)讀寫(xiě)ISA地址，測(cè)得的結(jié)果是當(dāng)進(jìn)行字(WORD)讀寫(xiě)時(shí)，應(yīng)用程序直接訪(fǎng)問(wèn)ISA外設(shè)地址比調(diào)用設(shè)備驅(qū)動(dòng)API函數(shù)快10倍以上，當(dāng)時(shí)行字節(jié)(BYTE)讀寫(xiě)時(shí)，應(yīng)用程序直接訪(fǎng)問(wèn)ISA外設(shè)地址比調(diào)用設(shè)備驅(qū)動(dòng)API函數(shù)快15倍以上。

下面是測(cè)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(fǎng)問(wèn)方式的測(cè)試結(jié)果：

要實(shí)現(xiàn)應(yīng)用程序直接訪(fǎng)問(wèn)ISA外設(shè)地址空間需要更新ISA驅(qū)動(dòng)程序，需要的用戶(hù)可與英創(chuàng)聯(lián)系。

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