LittleFS and Flash Memory - Notes and Lessons

The LittleFS filesystem is used to provide a layer on top of the raw flash memory module (block device) which allows for files/folders, and other standard filesystem features (reading, appending, etc.).

Flash Memory Module

• Chip: MT29F1G 1Gib (128MiB)
  • NAND FLASH
  • Datasheet: https://www.farnell.com/datasheets/3151163.pdf
• SPI DMA is faster.
• The MT29F1G chip requires that the CS line be driven to inactive between writes, otherwise the chip/system goes unresponsive.

LittleFS

• Solid filesystem once everything is implemented right.
• Uses Copy-on-Write. Thus, modifying a file takes a long time as its block(s) get copied.

LittleFS Configuration

• metadata_max is an important configuration variable.
  • Decrease the time metadata compaction operations take (operation is very slow).
  • Required to prevent watchdog trigger loop (i.e., prevents extremely-long writes).
  • See: https://github.com/littlefs-project/littlefs/issues/1079#issuecomment-2720048008
  • Alternative/additional option described in issue: Call lfs_fs_gc() periodically during idle.
  • Default value is the entire blocksize. We lower it to: .metadata_max = 1024 * 8