MMC Card Reader Development

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This wiki describes the development of the MMC Card Reader Project

Contents

Architecture

  • See here for block diagram


Development Roadmap

Phase 1

  • Create fatfs wrapper for file system in freertos_posix
  • Use existing I2C EEPROM driver for development purpose

Phase 2

  • Circuit design for interfacing MMC

Phase 3

  • SPI driver for MMC

Phase 4

  • Test for normal read/write function
  • hotswap (should not hang or cause voltage dip)
  • multiple file read/write (protection)


Circuit and PCB


Software Implementation

  • Use FatFs for accessing FAT16 file system.
  • Create a FatFs Wrapper in freertos_posix as an intermediate layer to map API in stdio.h to API in FatFs, for example:
 +--------------------------------------------+
 | POSIX              fopen()                 |
 |                       |                    |
 |                      \|/                   |
 |                     open()                 |
 |                       |                    |
 |                      \|/                   |
 +--------------------------------------------+
 | FatFs Wrapper    fatfs_open()              |
 |                       |                    |
 |                      \|/                   |
 +--------------------------------------------+
 | FatFs              f_open()                |
 |                       |                    |
 |                      \|/                   |
 |                disk_initialize()           |
 |                       |                    |
 |                      \|/                   |
 +--------------------------------------------+
 | EEPROM         i2c_eeprom_open()           |
 +--------------------------------------------+


Comparison of stdio and FatFs API

  • selected list for concern
Function stdio.h FatFs Remarks
Open
 FILE * 

fopen (

 const char * filename, 
 const char * mode
 

);

 FRESULT 

f_open (

 FIL* FileObject,       /* Pointer to the blank file object structure */
 const XCHAR* FileName, /* Pointer to the file neme */
 BYTE ModeFlags         /* Mode flags */

);

  • FILE matches FIL
  • filename matches FileName
  • mode matches ModeFlags
  • stdio.h has no equivalent FRESULT
Read
 size_t 

fread (

 void * ptr, 
 size_t size, 
 size_t count, 
 FILE * stream 

);

 FRESULT 

f_read (

 FIL* FileObject,    /* Pointer to the file object structure */
 void* Buffer,       /* Pointer to the buffer to store read data */
 UINT ByteToRead,    /* Number of bytes to read */
 UINT* ByteRead      /* Pointer to the variable to return number of bytes read */

);

  • size_t matches ByteRead
  • ptr matches Buffer
  • count matches ByteToRead
  • stream matches FileObject
  • stdio.h has no equivalent FRESULT
Write
 size_t 

fwrite (

 const void * ptr, 
 size_t size, 
 size_t count, 
 FILE * stream 

);

 FRESULT 

f_write (

 FIL* FileObject,     /* Pointer to the file object structure */
 const void* Buffer,  /* Pointer to the data to be written */
 UINT ByteToWrite,    /* Number of bytes to write */
 UINT* ByteWritten    /* Pointer to the variable to return number of bytes written */

);

  • size_t matches ByteWritten
  • ptr matches Buffer
  • count matches ByteToWrite
  • stream matches FileObject
  • stdio.h has no equivalent FRESULT
Close
 int 

fclose (

 FILE * stream 

);

 FRESULT 

f_close (

 FIL* FileObject     /* Pointer to the file object structure */

);

  • int matches FRESULT
  • stream matches FileObject
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