FatFs is an open-source library for File Allocation Table (FAT) file systems. This example features a memory card interface and implements the FatFs library for FAT file system access via the PIC18F56Q71 microcontroller. The microcontroller creates a demo info file and then logs the microcontroller's die temperature every 30s.
- Petit FatFs on a Memory Card with PIC18F56Q71
- This example has a smaller memory footprint, but has notable limitations as a result
- MPLAB® X IDE v6.20 or newer
- MPLAB XC8 v2.46 or newer
- MPLAB Code Configurator (MCC)
- FatFs R0.15 (Included in Project)
- PIC18F56Q71 Curiosity Nano Evaluation Kit (EV01G21A)
- Curiosity Nano Base for Click Boards™
- MICROSD Click (MIKROE-924)
- Memory Card
- Significantly improved compatability with memory cards
- Added option to print the sector data
- Added hex viewer for sector data
- Modified defines to match specification
- Reduced clock frequency from 10.4 MHz to 8 MHz for more compatability
With the power off, plug in the Curiosity Nano into the adapter board. Put the MICROSD Click in slot 1.
Before use, format the memory card as a FAT volume. FatFs does not need a file to be preloaded for this example.
- Plug in the Curiosity Nano.
- Open MPLAB X IDE.
- Click the MPLAB Data Visualizer button in the toolbar.
- Press the gear symbol on the COM port associated with the Curiosity Nano.
- Set the baud rate to 115200.
- Click the terminal button to connect the COM port to the serial terminal.
Data will print when a memory card is inserted, as shown below.
FatFs handles file system management, but does not handle communication with the memory card. The library requires the following functions to be implemented:
disk_initializedisk_readpdisk_writepdisk_statusdisk_ioctl
These functions call the memory card API to perform file system tasks.
When a memory card is inserted, a switch in the socket pulls a detection line low. The microcontroller debounces this signal, then sets a flag to initialize the memory card outside of the interrupt handler. When inserted, the card may fail to initialize due to powering on delays, but the program will retry multiple times before erroring out.
Communication with the memory card is via Serial Peripheral Interface (SPI). A series of commands are sent to the card to configure and prepare it for file read/write. For commands, the clock frequency is 400 kHz. During memory read/write, the clock frequency is increased to 8 MHz, depending on the memory card's indicated maximum. Reads and writes have a time-out to prevent an infinite waiting loop, in the event of a faulty memory card.
Pressing SW0 will cause the microcontroller to unmount the memory card, allowing it to be safely removed. This is necessary in this example due to the regular writes to the memory card. However, the lightweight example does not run write continuously, and thus does not have this restriction.
When a memory card is inserted, the program will initialize the card with the function disk_initialize. If the disk is initialized successfully, the program will look for the file DEMO.HTM. If the file does not exist, it will be automatically created and filled with links to resources about this example.
After this, the program will create or append the file LOG.CSV on the memory card. Every 30s, the program logs the current die temperature of the microcontroller, along with the sample number. LED0 toggles every time a value is logged.
Note: Since file operations occur regularly, it is recommended to press SW0 to stop file operations before removing the card.
Macro (memCard.h) |
Value | Description |
|---|---|---|
| MEM_CARD_DEBUG_ENABLE | Defined | Prints debug messages. If not defined, memory usage and performance will improve. |
| MEM_CARD_FILE_DEBUG_ENABLE | Defined | Prints file operation requests. If not defined, memory usage and performance will improve. |
| MEM_CARD_SECTOR_DEBUG_ENABLE | Not defined | Prints the sector data received from the memory card and implements a basic hex viewer for troubleshooting. If not defined, memory usage and performance will significantly improve. |
| MEM_CARD_CRC_DEBUG_ENABLE | Not defined | Prints the CRC on sector reads to the terminal. If not defined, memory usage and performance will improve. |
| MEMORY_CARD_IDLE_CLOCK_CYCLES | 10 | Number of "dummy" bytes to send between each command |
| R1_TIMEOUT_BYTES | 10 | How many bytes to wait for a valid response code |
| DEFAULT_READ_TIMEOUT | 250 | Sets the maximum length of time in milliseconds for a read operation to complete |
| DEFAULT_WRITE_TIMEOUT | 500 | Sets the maximum length of time in milliseconds for a write operation to complete |
| INIT_RETRIES | 100 | How many times to try and send the initization command to the memory card |
| FULL_RETRIES | 5 | Sets the number of times the system will attempt to initialize the memory card |
| DISABLE_SPEED_SWITCH | Not defined | If defined, the card will remain at 400 kHz speeds for all communication. This will impact performance of read/write operations. |
| CRC_VALIDATE_READ | Defined | If defined, block reads will verify the Cyclic Redundancy Check (CRC) of the data. To reject bad data, set ENFORCE_DATA_CRC. |
| ENFORCE_DATA_CRC | Defined | If defined, block reads with a bad CRC will fail |
Macro (demo.h) |
Value | Description |
|---|---|---|
| PRINT_TEMP_RESULTS | Not defined | If defined, each new log entry is also printed to the serial terminal |
| INFO_FILE_NAME | 1:/INFO.HTM | File path of the info file |
| LOG_FILE_NAME | 1:/LOG.CSV | File path of the log file |
Note: FatFs has a set of macros to modify functionality and/or memory usage. See ffconf.h for more information.
- FatFs will only create files with full capitialized names (e.g., test.txt → TEST.TXT)
- Attempting to write more than
FAT_BLOCK_SIZEbytes in one operation will cause zeros to fill the sectors between the first and last written- Work around: Split a long write into
FAT_BLOCK_SIZEbyte chunks (seeDemo_createInfoFilefor sample implementation)
- Work around: Split a long write into
This example has demonstrated how to implement FatFs on the PIC18F56Q71 family of microcontrollers to log microcontroller die temperature over a period of time.