A useful feature of the esp32 is the ability to use some of the flash memory as a file system. This is accessed using standard 'read' and 'write' commands (amongst others) and data can also be written to he 'disk' space from a PC.
Multiple files can be used - and it ideal for loggers / html pages etc. Data is non-volatile, so is stored between restarts / power cycles etc. Note that directories are not supported.
I wrote a small program that accesses this - here it initialises the SPIFFS data area (and formats it if needed) - and displays the size and used space. Then in this tiny example it writes the text file twi.h to UART. (twi.h was written to the storage from windows)
Anyone any comments - ideas. As it stands it can easily be converted to a component. I think some directory operations (getting the list of files for example) are possible.
I've added several macros - to open, close and read/write strings or data as an array - a natural addition would be macros to read / write a byte of data. Also Seek.
To test.
The esp32 needs to have a SPIFFS partition allocated. In the program directory (in my case r:\spiffs) write the following as partitions.csv
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# Name, Type, SubType, Offset, Size, Flags
# Note: if you have increased the bootloader size, make sure to update the offsets to avoid overlap
nvs, data, nvs, 0x9000, 0x6000,
phy_init, data, phy, 0xf000, 0x1000,
factory, app, factory, 0x10000, 1M,
storage, data, spiffs, , 0xF0000,
Then point the idf to the new partitions table using idf.py menuconfig (under partition table - set to custom and point Custom csv to your file)
Now when you compile and upload the program it will allocate the data as per partitions.csv
If you upload the program now and watch the UART output - it will format the SPIFFS area.
Creating and uploading the spiffs data area.
Copy all the files to a directory and then use mkspiffs (note I had to find a copy (and there is one in the Arduino IDE directories (but not in the espressif framworks))
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mkspiffs.exe -c . -b 4096 -p 256 -s 0xF0000 spiffs.binThe data is uploaded using esptool
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esptool -p COM4 -b 512000 write_flash 0x110000 spiffs.binThe simple program only outputs a text file (files support the usual C file modes "r", "w", "a" and "rb", "wb", "ab"') - this is hardcoded as twi.h - adjust to suit. File writing also works okay.. Please test and report on the other functions...
Martin