Brush Electronics

This code is an implementation of the ELM Generic File System module which has been ported to the Microchip PIC24/dsPIC33 series microcontrollers with the Microchip C30, XC16 and CCS PCD compilers and the PIC18F series Microcontrollers with the CCS PCH compiler. The drivers for the PIC18 and PIC24/dsPIC33 have been extensively debugged and modified.

For the PIC18F series microcontrollers, the driver is supplied with a hybrid Data Logger application, which also features a DOS like command line interface incorporating a software real time clock (highly desirable for a file system). The data logger application, based on a real logger, was designed to record 12 bytes of data every 50ms and was tested successfully at 12 bytes per 10ms. However, the actual performance depends on many factors such as microcontroller clock speed, SPI bus speed, memory card access speed and other tasks being handled by the microcontroller. The data logger application demonstrates the concept of caching the incoming raw data while SD/MMC write operations of the data are in effect. Note that this is a proof of concept application. The marriage of the data logger function and the DOS command line interface are intended to show the developer how to use the various functions.

The file system drivers support standard (high performance) and LITE configuration modes. The standard mode implements a separate 512 byte read/write buffer for the file system and for each file. The LITE mode, enabled via a #define directive in the source code, offers all the features of the standard mode and is well suited to applications and controllers that have limited RAM available. The LITE mode shares a single 512 byte read/write buffer between the file system and all open files and is capable of supporting hundreds of files open concurrently. For high performance applications that require two or more files open concurrently, the standard mode is highly recommended.

     RAM requirements:         Standard           Lite
     File System overhead        560              560
     Per File Overhead           540               38

Subset of file specific functions:

• FRESULT f_read (FIL *fp, void *buff, WORD btr, WORD *br); // Read from a file 
  FRESULT f_close (FIL *fp); // Close a file 
  FRESULT f_lseek (FIL *fp, DWORD ofs); // Seek file pointer 
  FRESULT f_stat (char *path, FILINFO *finfo); // Get file status
  FRESULT f_opendir (DIR *scan, char *path); // Initialize to read a directory
  FRESULT f_readdir (DIR *scan, FILINFO *finfo); // Read a directory item
  FRESULT f_getfree (DWORD *nclust); // Get number of free clusters 
  FRESULT f_mountdrv (void); // Force initialize the file system 
  void f_get_error_mesg(FRESULT Mesg, char *destination); // Convert the FRESULT return code to a string 
  FRESULT f_write (FIL *fp, void *buff, WORD btw, WORD *bw); // Write file 
  FRESULT f_sync (FIL *fp); // Flush cached information of a writing file 
  FRESULT f_unlink (char *path); // Delete a file or directory 
  FRESULT f_mkdir (char *path); // Create a directory 
  FRESULT f_chmod (char *path, BYTE value, BYTE mask); // Change file attriburte  
  FRESULT f_rename ( char *path_old, char *path_new); // Rename a file / directory
  FRESULT f_open (FIL *fp, char *path, BYTE mode); // Open or create a file

For the PIC24/dsPIC33 series microcontrollers, the driver is supplied with a sample application which features a DOS like command line interface.

Sample CLI commands:

• CREATE name – create the file ‘name’ 
  DATE [dd/mm/yy] – set / display time  
  COPY src dst – copy file ‘scr’ to ‘dst’ 
  DIR – list directory 
  DUMP name – hex dump file ‘name’ 
  EXPLORE – explores the SD card data structure 
  INIT – initialise the SD card file system data structures 
  LOG [START|STOP] – display / change logging status 
  MD name – create directory ‘name’ 
  RESET – reset the PIC Microcontroller 
  STATUS – display system status 
  TIME – set / display time  
  TYPE name – list contents of text file ‘name’
  DELETE name – delete the file ‘name’

Aside from hardware and software challenges, the integration of SD and MMC cards in embedded systems is not without headaches. Licenses for integration of SD Cards or MMC Cards into products may be required from Microsoft, IBM, the SD Card Association (for SD Cards) and the Multimedia Association (for MMC Cards).

Microsoft has been granted patents covering the File Allocation Table (FAT) file system. These patents pertain to the integration of long file names with legacy DOS file names in the same data structure. In order to avoid infringing on Microsoft’s patents in this area, our software does not support long file names nor does it support formatting the media. IBM holds patents pertaining to extended file system attributes. Our code does not support extended file attributes.

It is up to the purchaser of this software to ascertain for themselves if licenses are required from any or all of these or other organizations for the integration of the media or our software into their products. In the event licenses are required from any of these or other organizations, it is up to the purchaser of this software to acquire, at their own cost, such licenses directly from the license holders.