精简ISA总线是英创工控主板的特色之一,我们基于ISA总线推出了多串口、多网口、多CAN接口等扩展模块,我们的很多用户也基于ISA总线设计了自己的专有扩展单元并取得了成功。为了充分发挥ISA总线的性能,对于ISA总线的访问,我们除了提供最基本的设备驱动API操作函数外,还先后增加了ISA总线的块读写操作方法和ISA总线的DMA操作方法。当ISA总线以DMA方式进行数据传输时,在最大限度的利用ISA总线带宽的同时,又减少了ISA操作占用CPU的时间,所以利用DMA是进行批量数据传输时的首选方式。
在实际的应用中,除了成批量的数据访问外,也可能会存在对外设进行频繁的字或字节访问。英创主板的ISA总线周期通常在200ns左右,而应用程序调用一次设备驱动程序API(WriteFile,ReadFile)花费的时间却需要数微秒的时间,这显然大大降低了对外设单字(或单字节)的访问效率。为了解决这一问题,我们利用了WinCE的虚拟地址映射技术,在ISA驱动程序中实现了在使用ISA的应用进程地址空间内分配一段虚拟地址空间,并将其与ISA接口的物理地址空间进行了绑定。简单来讲就是实现了在WinCE应用程序中可以直接访问ISA总线的外设地址空间,从使用的角度看,我们实现了以下5个函数。ISAMmMap用于获得ISA总线的基地址,其余4个函数分别为字读/写和字节读/写操作函数。
HANDLE ISAMmMap(HANDLE hISA); // 映射ISA总线物理地址空间 BYTE ISARead8(HANDLE hMmMap, DWORD dwPortOffset); // 读单字节 void ISAWrite8(HANDLE hMmMap, DWORD dwPortOffset, BYTE ucValue); // 写单字节 WORD ISARead16(HANDLE hMmMap, DWORD dwPortOffset); // 读单字 void ISAWrite16(HANDLE hMmMap, DWORD dwPortOffset, WORD wValue); // 写单字 |
下面是上述5个函数实现的源代码,在ISAMmMap函数中调用DeviceIoControl,通过IOCTL_VIRTUAL_COPY_EX命令获取ISA总线的基地址。
// 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, //打开“ISA1:”返回的Handler IOCTL_VIRTUAL_COPY_EX, // IOCTL命令码 NULL,0, // 不使用输入参数 &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); } |
我们在ESM3352上,分别测试了利用地址映射方法直接访问ISA外设地址和调用设备驱动API函数读写ISA地址,测得的结果是当进行字(WORD)读写时,应用程序直接访问ISA外设地址比调用设备驱动API函数快10倍以上,当时行字节(BYTE)读写时,应用程序直接访问ISA外设地址比调用设备驱动API函数快15倍以上。
下面是测试程序源代码:
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 { 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 { 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 { 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 { 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上两种访问方式的测试结果:
要实现应用程序直接访问ISA外设地址空间需要更新ISA驱动程序,需要的用户可与英创联系。
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