英创嵌入式主板精简ISA总线时序及基本编程方法

精简ISA总线信号

英创公司的嵌入式主板产品，如ESM7000、ESM335x等，均配置有精简ISA总线接口，基本的精简ISA总线由8位地址数据总线（分时复用）+ 4条控制信号组成，通过异步操作的读写总线周期，来实现对外部逻辑单元的控制。精简ISA总线的最大优点是硬件接口简单、应用程序接口简单，读写速度可达4MB/s，特别适合在嵌入式系统中使用。实现主板与用户专用接口电路的控制与数据传输。

精简ISA总线核心的12条信号线定义如下：

信号名称	信号功能简要说明
ISA_AD0	地址数据总线，LSB
ISA_AD1	地址数据总线
ISA_AD2	地址数据总线
ISA_AD3	地址数据总线
ISA_AD4	地址数据总线
ISA_AD5	地址数据总线
ISA_AD6	地址数据总线
ISA_AD7	地址数据总线，MSB
ISA_RDn	总线数据读控制信号，低电平有效
ISA_WEn	总线数据写控制信号，低电平有效
ISA_ADVn	总线地址锁存控制信号，低电平有效
ISA_CSn	总线周期片选控制信号，低电平有效

上表的12条信号直接从ESMARC主板引出，再配置上总线复位信号和中断信号（通常由主板的GPIO信号来实现），就可驱动各种接口单元了。

精简ISA总线时序

基本的总线时序包括读总线周期和写总线周期。以下时序来自ESM7000嵌入式主板的精简ISA总线，ESM335x的精简ISA总线时序也完全同样的，其扩展外设逻辑电路可直接互换。

异步读总线周期时序

异步写总线周期时序

对异步读写操作，一个完整的读写操作时间包括上述的总线操作周期和总线周期间隔，大约在240ns – 250ns，对应着4MB/s – 4.2MB/s的数据读写速度。锁存的地址也是8-bit，对应精简ISA总线的寻址能力是256个8-bit寄存器，这对绝大多数嵌入式应用已足够使用。

WinCE平台编程方法

ESM7000和ESM335x均支持Windows CE平台（WEC7），对精简ISA总线配置了相应的驱动程序。用户的应用程序只需通过对其驱动程序进行操作，即可实现对ISA总线的读写操作。为方便应用调用，封装了几个基本操作函数：

HANDLE  ISA_Open( LPCWSTR lpDevName )
{return CreateFile(lpDevName,            // name of deviceGENERIC_READ|GENERIC_WRITE,         // desired accessFILE_SHARE_READ|FILE_SHARE_WRITE,   // sharing modeNULL,                               // security attributes (ignored)OPEN_EXISTING,                      // creation dispositionFILE_FLAG_RANDOM_ACCESS,            // flags/attributesNULL);
}BOOL    ISA_Close( HANDLE hISA)
{return CloseHandle( hISA );
}BOOL    ISA_ReadUchar(HANDLE hISA, DWORD dwPortOffset, PBYTE pBuf)
{DWORD dwBufSize = sizeof(BYTE);DWORD dwNbBytesRead = 0;*pBuf = (BYTE)(dwPortOffset & 0xFF);return ReadFile(hISA, pBuf, dwBufSize, &dwNbBytesRead, NULL);
}BOOL    ISA_WriteUchar(HANDLE hISA, DWORD dwPortOffset, BYTE ucValue)
{WORD  wValue;DWORD dwBufSize = sizeof(WORD);DWORD dwNbBytesWritten = 0;wValue = (WORD)(dwPortOffset & 0xFF);wValue = (wValue << 8) | ucValue;return WriteFile(hISA, &wValue, dwBufSize, &dwNbBytesWritten, NULL);
}BOOL    ISA_ReadWord(HANDLE hISA, DWORD dwPortOffset, WORD* pBuf)
{DWORD dwBufSize = sizeof(WORD);DWORD dwNbBytesRead = 0;*pBuf = (WORD)(dwPortOffset & 0xFE);return ReadFile(hISA, pBuf, dwBufSize, &dwNbBytesRead, NULL);
}BOOL    ISA_WriteWord(HANDLE hISA, DWORD dwPortOffset, WORD wValue)
{DWORD dwValue;DWORD dwBufSize = sizeof(DWORD);DWORD dwNbBytesWritten = 0;dwValue = (dwPortOffset << 16) | wValue;return WriteFile(hISA, &dwValue, dwBufSize, &dwNbBytesWritten, NULL);
}

打开设备文件Handle

HANDEL hISA = ISA_Open( _T("ISA1:"));
if( hISA == INVALID_HANDLE_VALUE) {// error processing
}

读操作

    DWORD   dwPortOffSet = 0;  // 0x00 .. 0xFFBYTE    ucValue;WORD    wValue;BOOL    bRet;// read a bytebRet = ISA_ReadUchar(hISA, dwPortOffSet, &ucValue);// read a wordbRet = ISA_ReadWord(hISA, dwPortOffSet, &wValue);

写操作

    DWORD   dwPortOffSet = 0;  // 0x00 .. 0xFFBYTE    ucValue = 0x55;WORD    wValue = 0x55aa;BOOL    bRet;// write a bytebRet = ISA_WriteUchar(hISA, dwPortOffSet, ucValue);// write a wordbRet = ISA_WriteWord(hISA, dwPortOffSet, wValue);

关闭设备文件Handle

ISA_Close(hISA);

Linux平台编程方法

ESM7000和ESM335x均支持Linux平台（Linux-4.x.x），对精简ISA总线配置了相应的驱动程序。在为用户的应用程序封装的函数中，除支持常规的端口读写外，同时支持了Linux特有的mmap操作，以提高读写速度。封装函数如下：

unsigned char *isa_base = NULL;
unsigned int  map_size = 4096;// return >= 0: return file handle
// return < 0: return failed code
int isa_open()
{int fd;fd = open("/dev/em_isa", O_RDWR);if(fd < 0) {return fd;}isa_base = (unsigned char*)mmap(0,map_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);if (isa_base == MAP_FAILED) {printf("%s mmap failed\n", __func__);isa_base = NULL;close(fd);return -1;}return fd;
}int isa_close(int fd)
{if(isa_base != NULL) {munmap(isa_base, map_size);isa_base = NULL;}return close(fd);
}// offset: port address in isa bus
unsigned char isa_read(int fd, unsigned int offset)
{unsigned char val_b;int           rc;offset &= 0xff;if(isa_base != NULL) {unsigned short int val_w;val_w = *((unsigned short int*)(isa_base + (offset << 1)));val_b = (unsigned char)(val_w & 0xff);return val_b;}val_b = offset;rc = read(fd, &val_b, sizeof(unsigned char));if(rc < 0) {// read errorprintf("%s failed %d\n", __func__, rc);}return val_b;
}// offset: port address in isa bus
void isa_write(int fd, unsigned int offset, unsigned char val_b)
{unsigned short int val_w;int                rc;offset &= 0xff;if(isa_base != NULL) {val_w = val_b;*((unsigned short int*)(isa_base + (offset << 1))) = val_w;return;}val_w = ((offset & 0xff) << 8) | val_b;rc = write(fd, &val_w, sizeof(unsigned short int));if(rc < 0) {// write errorprintf("%s failed %d\n", __func__, rc);}
}// offset: port address in isa bus
unsigned short int isa_read16(int fd, unsigned int offset)
{unsigned short int val_w;int                rc;// 2-byte alignment is required for offsetoffset &= 0xfe;if(isa_base != NULL) {unsigned int val;val = *((unsigned int*)(isa_base + (offset << 1)));val_w = (unsigned short int)((val >> 8) | (val & 0x00ff));return val_w;}val_w = (unsigned short int)offset;rc = read(fd, &val_w, sizeof(unsigned short int));if(rc < 0) {// read errorprintf("%s failed %d\n", __func__, rc);}return val_w;
}// offset: port address in isa bus
void isa_write16(int fd, unsigned int offset, unsigned short int val_w)
{unsigned int val;int          rc;// 2-byte alignment is required for offsetoffset &= 0xfe;if(isa_base != NULL) {val = val_w;val = ((val << 8) & 0x00ff0000) | (val & 0x000000ff);*((unsigned int*)(isa_base + (offset << 1))) = val;return;}val = (offset << 16) | val_w;rc = write(fd, &val, sizeof(unsigned int));if(rc < 0) {// write errorprintf("%s failed %d\n", __func__, rc);}
}

打开设备文件Handle

//open file
int fd = isa_open();
if(fd < 0) {//open file failedprintf("open file = %d\n", fd);return fd;
}

读操作

    unsigned int offset = 0x00;unsigned int value;// read a bytevalue = isa_read(fd, offset);// read a wordvalue = isa_read16(fd, offset);

写操作

    unsigned int offset = 0x00;unsigned int value = 0x55aa;// write a byte, lower bytevalue = isa_write(fd, offset, value);// write a wordvalue = isa_write16(fd, offset, value);

关闭设备文件Handle

    isa_close(fd);