QSPIFileSystem Class Reference

Access the filesystem on an QSPI flash using SPIFI. More...

#include <QSPIFileSystem.h>

Detailed Description

Access the filesystem on an QSPI flash using SPIFI.

One way to utilize the 8MByte of QSPI FLASH on the LPC4088 QuickStart Board is to place a file system on it. The QSPIFileSystem is using the FileSystemLike interface making using it is as simple as:

 #include "mbed.h"
 #include "QSPIFileSystem.h"

 QSPIFileSystem qspifs("qspi");
  
 int main() {
     if (!qspifs.isformatted()) {
         qspifs.format();
     }

     FILE *fp = fopen("/qspi/myfile.txt", "w");
     if (fp != NULL) {
         fwrite("Hello World!", 12, 1, fp);
         fclose(fp);
     }
 }

The file system can be formatted to a specific size in increments of 1MByte and will allways be placed at the top of the address range. For the 8 MByte memory on the LPC4088 QuickStart Board this means:

                    0x28000000                                               0x28800000
                         |------|------|------|------|------|------|------|------|
 qspifs.format(1)        |   available for program                        |  FS  |
                         |------|------|------|------|------|------|------|------|
                                                                                  

                         |------|------|------|------|------|------|------|------|
 qspifs.format(2)        |   available for program                 | FileSystem  |
                         |------|------|------|------|------|------|------|------|
                                                                                  

                         |------|------|------|------|------|------|------|------|
 qspifs.format(7)        | PROG |                 FileSystem                     |
                         |------|------|------|------|------|------|------|------|
                                                                                  

                         |------|------|------|------|------|------|------|------|
 qspifs.format(8)        |                       FileSystem                      |
                         |------|------|------|------|------|------|------|------|
 

The file system must be placed at the top of the memory because the linker scripts places your program at the bottom of the memory (if needed).

The file system is using one or more blocks (each the size of one erase block) per file. Each file is stored in a sequence of blocks. If a file is written to so that it's size will occupy more than one block and the block after is already used by a different file the entire file will be moved, like this:

                   |-------|-------|-------|-------|-------|-------|-------|
 Before            |///////| FILE1 | FILE2 | FILE3 |///////|///////|///////|
                   |-------|-------|-------|-------|-------|-------|-------|
                                                                            

 After writing     |-------|-------|-------|-------|-------|-------|-------|
 to FILE2          |///////| FILE1 |///////| FILE3 |     FILE2     |///////|
                   |-------|-------|-------|-------|-------|-------|-------|
 

Note: As each file takes up at least one block it will limit the total number of files that can be stored on the file system. The formula for this is roughly

          max_num_files = fs_size_in_bytes / erase_block_size
 

For the SPI flash on the LPC4088 QuickStart Board it means

          max_num_files = 8MByte / 4KByte = 2048
 

Some of the blocks are used to store the table of content (TOC) at the very end of the spi flash. The TOC will contain a list of all blocks on the flash (even those not used by the file system) and will mark each block as "reserved","in use" or "free". For a file system that is 4MByte on a 8MByte flash half of the blocks will be marked as "reserved".

Note: The file system will not store any date/time information.

Note: The file system will not store any file attributes (hidden/system/read only).

Note: The file system stores the absolute path of each file (path + file name) in the file's first block's first 256 bytes. Folders are never stored themselves. This has the drawback that the file system cannot hold empty folders.

Definition at line 112 of file QSPIFileSystem.h.

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