How to Implement File Systems on Embedded Flash in Your Firmware

Overview of File Systems for Embedded Flash

• Embedded systems may use NOR or NAND flash memory, each with unique characteristics impacting file systems used.

 

• SPIFFS, LittleFS, and FatFS are popular file systems for embedded environments due to their efficiency and flash-specific optimizations.

Considerations Before Implementation

• Understand the hardware-specific limitations, such as flash block size and endurance cycles.

 

• Review the memory footprint and CPU overhead that each file system library adds to ensure it fits the system constraints.

Installing the File System Library

• Download the chosen file system library (e.g., SPIFFS, LittleFS) and include it in your project correctly referencing header files and source files in your build setup.

#include <spiffs.h>
spiffs fs;

Configuring the File System

• Define the logical parameters and link them to the hardware specifics, including the flash address mapping and sizes.

 

• Modify the configuration structure provided by the library to suit your flash memory's characteristics, such as block size and page size.

spiffs_config cfg;
cfg.phys_size = 2 * 1024 * 1024; // Use a 2MB flash memory
cfg.phys_addr = 0;               // Start at address 0
cfg.phys_erase_block = 4096;     // Block size
cfg.log_block_size = 4096;
cfg.log_page_size = 256;

Mounting the File System

• Use the library functions to mount the file system. Initialize any necessary buffers or callbacks required by the library.

 

• Verify the return status after mounting to ensure the file system was initialized correctly.

spiffs_mount(&fs, &cfg, my_spiffs_work_buf,
             my_spiffs_fds, sizeof(my_spiffs_fds),
             my_spiffs_cache_buf, sizeof(my_spiffs_cache_buf), 0);

File Operations Implementation

• Implement file opening, reading, writing, and closing using the file system library APIs.

 

• Handle return statuses effectively to manage errors like file not found or no space left on the device.

 

• Consider implementing a wrapper for these operations to simplify the handling of errors and improve code maintainability.

spiffs_file fd = SPIFFS_open(&fs, "myfile.txt", SPIFFS_CREAT | SPIFFS_RDWR, 0);
// Check if fd is valid
SPIFFS_write(&fs, fd, (u8_t *)buf, buf_len);
SPIFFS_close(&fs, fd);

Formating and Maintenance

• Implement the formatting process using file system functions if the memory is corrupted or during the first boot to set up a clean system.

 

• Periodic maintenance operations such as checking the health of the file system or cleaning up unused data blocks can help maintain performance over time.

SPIFFS_format(&fs); // Format the file system

Testing and Validation

• Thoroughly test file operations under realistic usage scenarios to validate data integrity and flash wear leveling.

 

• Simulate power failures and extreme conditions to ensure the robustness of your implementation.

Optimization Tips

• For performance-critical applications, optimize read and write operations by tuning cache size and configuration parameters.

 

• Compile with optimization flags suitable for your embedded platform to decrease execution time and memory usage.