为STM32移植FATFS，读取SD卡上FAT12/16/32文件系统

给stm32移植fatfs文件系统，今天终于取得阶段性胜利。只需要提供这样几个函数即可 

DSTATUS disk_initialize (BYTE); 
DSTATUS disk_status (BYTE); 
DRESULT disk_read (BYTE, BYTE*, DWORD, BYTE); 
DRESULT disk_write (BYTE, const BYTE*, DWORD, BYTE); // 如果实现只读的文件系统就不需要了。 
DRESULT disk_ioctl (BYTE, BYTE, void*); 

移植成功后，可以用如下方式读取SD卡了，实在太方便了，和PC机上编程差不了多少。 

   

 unsigned int i; 
    BYTE buffer[512];    // file copy buffer 
    FATFS fs;            // Work area (file system object) for logical drive 
    FIL fsrc;            // file objects 
    FRESULT res;         // FatFs function common result code 
    UINT br;             // File R/W count 
    USART1_Puts("Now, I'll read file 'i2c/uart.lst'.\n"); 

    // Register a work area for logical drive 0 
    f_mount(0, &fs); 

    // Open source file 
    res = f_open(&fsrc, "i2c/uart.lst", FA_OPEN_EXISTING | FA_READ); 
    if (res)  
    { 
        USART1_Puts("Can't open i2c/uart.lst for read. :-(\n"); 
        goto exit; 
    } 
     
    for (;;) { 
        res = f_read(&fsrc, buffer, sizeof(buffer), &br); 
        if (res || br == 0) break;   // error or eof 
        for( i = 0; i < br; ++i ) 
            USART1_Putc(buffer[i]); 
    } 
        
    f_close(&fsrc); 
exit: 
    // Unregister a work area before discard it 
    f_mount(0, NULL);