sd卡读写（fat文件系统）——sd example阅读

改mss后import example

主要是用fat的函数读写sd

fat文档：http://elm-chan.org/fsw/ff/00index_e.html

　　（1）f_mkdir清空sd卡，抄的时候记得把这个删掉。

　　（2）文件读写用的assic码，比如写的1，读出来%d的话是49，所以要处理一下字符串，可以用c的库函数atoi等。注意，读出来是有\r的，所以空白字符要滤掉的有：13，10，32

string/array to int/float
C/C++语言提供了几个标准库函数，可以将字符串转换为任意类型(整型、长整型、浮点型等)。

● atof()：将字符串转换为双精度浮点型值。
● atoi()：将字符串转换为整型值。
● atol()：将字符串转换为长整型值。
● strtod()：将字符串转换为双精度浮点型值，并报告不能被转换的所有剩余数字。
● strtol()：将字符串转换为长整值，并报告不能被转换的所有剩余数字。
● strtoul()：将字符串转换为无符号长整型值，并报告不能被转换的所有剩余数字

 　　(xil_printf除去了浮点的所有功能，转浮点的时候中间测试要用printf，不然%f输不出来（唉）)

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*版权这里可以忽略
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/*****************************************************************************/
/**
*这里的注释很重要，不能忽略
* @file xilffs_polled_example.c
*
*
* @note This example uses file system with SD to write to and read from
* an SD card using ADMA2 in polled mode.轮询读写adma2
* To test this example File System should not be in Read Only mode测试要求：文件系统不能只读
* To test this example USE_MKFS option should be true.zynq上需要选ues_mkfs
*

* This example was tested using SD2.0 card and eMMC (using eMMC to SD adaptor).
*
* To test with different logical drives, drive number should be mentioned in
* both FileName and Path variables. By default, it will take drive 0 if drive
* number is not mentioned in the FileName variable.板子选项里sd口有两个，需要选和对应
* For example, to test logical drive 1
* FileName =  "1:/<file_name>" and Path = "1:/"
* Similarly to test logical drive N, FileName = "N:/<file_name>" and
* Path = "N:/"
*
* None.
*
* <pre>
* MODIFICATION HISTORY:
*
* Ver   Who Date     Changes
* ----- --- -------- -----------------------------------------------
* 1.00a hk  10/17/13 First release
* 2.2   hk  07/28/14 Make changes to enable use of data cache.
* 2.5   sk  07/15/15 Used File size as 8KB to test on emulation platform.
* 2.9   sk  06/09/16 Added support for mkfs.
*
*</pre>
*
******************************************************************************/

/***************************** Include Files *********************************/

#include "xparameters.h"    /* SDK generated parameters */
#include "xsdps.h"        /* SD device driver */
#include "xil_printf.h"
#include "ff.h"
#include "xil_cache.h"
#include "xplatform_info.h"

/************************** Constant Definitions *****************************/


/**************************** Type Definitions *******************************/

/***************** Macros (Inline Functions) Definitions *********************/

/************************** Function Prototypes ******************************/
int FfsSdPolledExample(void);

/************************** Variable Definitions *****************************/
static FIL fil;        /* File object */
static FATFS fatfs;
/*
 * To test logical drive 0, FileName should be "0:/<File name>" or
 * "<file_name>". For logical drive 1, FileName should be "1:/<file_name>"
 */
static char FileName[32] = "Test.bin";//文件名
static char *SD_File;//申请指针
u32 Platform;//后面用来存平台的信息

#ifdef __ICCARM__
#pragma data_alignment = 32 //数据位数，后面根据平台信息变大小
u8 DestinationAddress[10*1024*1024];//读出数据
u8 SourceAddress[10*1024*1024];//源数据
#pragma data_alignment = 4 
#else
u8 DestinationAddress[10*1024*1024] __attribute__ ((aligned(32)));
u8 SourceAddress[10*1024*1024] __attribute__ ((aligned(32)));
#endif

#define TEST 7

/*****************************************************************************/
/**
*调用方法，想起了OO
* Main function to call the SD example.
*
* @param    None
*
* @return    XST_SUCCESS if successful, otherwise XST_FAILURE.
*
* @note        None
*
******************************************************************************/
int main(void)
{
    int Status;

    xil_printf("SD Polled File System Example Test \r\n");//这个是板子打出来的，要接串口

    Status = FfsSdPolledExample();
    if (Status != XST_SUCCESS) {
        xil_printf("SD Polled File System Example Test failed \r\n");
        return XST_FAILURE;
    }

    xil_printf("Successfully ran SD Polled File System Example Test \r\n");

    return XST_SUCCESS;

}

/*****************************************************************************/
/**
*
* File system example using SD driver to write to and read from an SD card
* in polled mode. This example creates a new file on an
* SD card (which is previously formatted with FATFS), write data to the file
* and reads the same data back to verify.
*写完读出并检查
* @param    None
*
* @return    XST_SUCCESS if successful, otherwise XST_FAILURE.
*
* @note        None
*
******************************************************************************/
int FfsSdPolledExample(void)
{
    FRESULT Res;//
    UINT NumBytesRead;
    UINT NumBytesWritten;
    u32 BuffCnt;
    u32 FileSize = (8*1024*1024);
    /*
     * To test logical drive 0, Path should be "0:/"
     * For logical drive 1, Path should be "1:/"
     */
    TCHAR *Path = "0:/";

    Platform = XGetPlatform_Info();//获得平台信息
    if (Platform == XPLAT_ZYNQ_ULTRA_MP) {//如果是ultra
        /*
         * Since 8MB in Emulation Platform taking long time, reduced
         * file size to 8KB.减大小
         */
        FileSize = 8*1024;
    }

    for(BuffCnt = 0; BuffCnt < FileSize; BuffCnt++){
        SourceAddress[BuffCnt] = TEST + BuffCnt;//给地址赋值，test应该是基地址？前面宏定义为7
    }

    /*
     * Register volume work area, initialize device
     */
    Res = f_mount(&fatfs, Path, 0);//初始化？文件系统指针（前面的静态变量），通道，模式
　　　　　　　　　　　　　　　　　　　　　　　　//fatfs在哪里赋的值？
　　　　　　　　　　　　　　　　　　　　　　　　//https://blog.csdn.net/lbaihao/article/details/75144011

    if (Res != FR_OK) { //失败
        return XST_FAILURE;
    }

    /*
     * Path - Path to logical driver, 0 - FDISK format.
     * 0 - Cluster size is automatically determined based on Vol size.
     */
    Res = f_mkfs(Path, 0, 0);//建立fat系统
    if (Res != FR_OK) {
        return XST_FAILURE;
    }

    /*
     * Open file with required permissions.
     * Here - Creating new file with read/write permissions. .
     * To open file with write permissions, file system should not
     * be in Read Only mode.
     */
    SD_File = (char *)FileName;//FileName是之前的常量"Test.bin"

    Res = f_open(&fil, SD_File, FA_CREATE_ALWAYS | FA_WRITE | FA_READ);//新建读写文件并打开，给指针fil
    if (Res) {
        return XST_FAILURE;
    }

    /*
     * Pointer to beginning of file .
     */
    Res = f_lseek(&fil, 0);//移到文件开始位
    if (Res) {
        return XST_FAILURE;
    }

    /*
     * Write data to file.写数据
     */
    Res = f_write(&fil, (const void*)SourceAddress, FileSize,
            &NumBytesWritten);//源数据要是const，第二个参数是buf，写的内容
    if (Res) {
        return XST_FAILURE;
    }

    /*
     * Pointer to beginning of file .
     */
    Res = f_lseek(&fil, 0);
    if (Res) {
        return XST_FAILURE;
    }

    /*
     * Read data from file.读数据
     */
    Res = f_read(&fil, (void*)DestinationAddress, FileSize,
            &NumBytesRead);
    if (Res) {
        return XST_FAILURE;
    }

    /*
     * Data verification 比较读写内容是否一致
     */
    for(BuffCnt = 0; BuffCnt < FileSize; BuffCnt++){
        if(SourceAddress[BuffCnt] != DestinationAddress[BuffCnt]){
            return XST_FAILURE;
        }
    }

    /*
     * Close file.关文件
     */
    Res = f_close(&fil);
    if (Res) {
        return XST_FAILURE;
    }

    return XST_SUCCESS;
}

 本次的sd就是把文件拷到sd上，命名。然后用open打开，读到数据，用dma写到ddr上。结束后用dma取出，写回到sd卡上。