Filesystem

Filesytem

Card detection

For detecting multi media cards, the basic programming guide of the OMAP35x technical reference manual was implemented (MMC/SD/SDIO). It should be noticed here that time is a important factor. It can happen that a SD card cannot be identified immediately, sometimes a process has to be repeated. This model includes initialization, detection, status, read and write functionality of MMCs.

FAT16

"FatFs" was used, to integrate FAT16. It is a generic FAT file system module and is completely decoupled from our system. Therefore the following functions had to be implemented to connect the module to our system:

disk_status - Get device status
disk_initialize - Initialize device
disk_read - Read sector(s)
disk_write - Write sector(s)
disk_ioctl - Control device dependent features
get_fattime - Get current time

With these functions implemented, the whole application interface can be used, including f_open, f_close, f_opendir and all the rest.

To open and read a file following routine was used. Of course it has to improved in the way of handling directories and files, but at this time, it works to read a file.

    // Fat file system object
    FATFS fs;
    fs.drv = 0;

    // Mount drive
    f_mount(&fs, "", 1);

    FILINFO fno;
    DIR dp;
    FRESULT res;
    unsigned ptr;

    // open and read root dir
    res = f_opendir(&dp, "/\0");
    if (res == FR_OK && f_readdir(&dp, &fno) == FR_OK) {
        //TODO: file only in root path!
        res = f_open(&file, fileName, FA_READ);

        if (!res) return;

        ptr = f_tell(&file); // get read-pointer
        f_read(&file, buffer, (uint32_t)bufferSize, &ptr); // read 4 byte
        *bufferSize = ptr;
        ptr = f_eof(&file); // check if eof is reached - if ptr != 0, go back
        f_lseek(&file, 0); // set read-pointer to the beginning of the file

        f_close(&file);
    }
    f_closedir(&dp);

Loader

The loader copies data from a given address and size into a temporary buffer and creates a new process. The new process starts at a fixed address:

#define CODE_START       0x00150000
#define CODE_MAIN_OFFSET 0xc

The buffered data is loaded into process space on the start address and its PC is set to the correct address. After this procedure the process state is set to READY and can be scheduled.

Work in progress

  • Detection of not only SD Card

We only implemented the detection of a SD 1.x card. Other card types or versions like a SDIO card or a SD 2.x card have to be integrated into the process of detection.

  • Write SD

Currently only blocks of MMCs can be read, but not be written. Therefore the writing function mmcsd_write_block_data has to implemented.

  • Time function

The function get_fattime has to be modified to fetch always the current time. At the moment it is using the same time.

  • Loader

Currently our loader can just handle one process, because only one buffer exists.