MMC Card Reader Development

This wiki describes the development of the MMC Card Reader Project

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

• SD Card connector
• SPI interface to main board

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