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FreeRTOS-Plus-FAT setup

FreeRTOS-Plus-FAT platform

Giving store-and-forward a real file backend. FreeRTOS-Plus-FAT covers what the adapter fills and what it leaves to you. This page is what you must supply around it.

The shape

SolidSyslogBlockStore
        │
SolidSyslogFileBlockDevice     ◀── sequence-numbered <prefix><NN>.log files
        │
SolidSyslogPlusFatFile         ◀── this adapter, over the ff_stdio API
        │
FreeRTOS-Plus-FAT core         ◀── vendor sources, you compile them
        │
your FF_Disk_t media driver    ◀── you write this

The adapter owns the middle box only. It speaks ff_stdio and never reaches the block device.

What you must provide

The FreeRTOS-Plus-FAT sources, compiled into your image. They are not clean under the conversion warnings this project builds with, so compile them under a relaxed warning set as you would the kernel itself.

An FF_Disk_t media driver for your storage hardware — the IO manager with its read and write block callbacks, the mount, format-on-first-use where no file system is present, and registration of the volume in the virtual file system. Plus-FAT ships reference drivers; its RAM disk is the clearest template.

A FreeRTOSFATConfig.h on your include path. Unlike some file systems this resolves off -I rather than needing to sit beside the sources. Set at least ffconfigBYTE_ORDER and ffconfigCWD_THREAD_LOCAL_INDEX; the defaults header fills the rest.

Kernel configuration, because Plus-FAT requires it:

  • recursive mutexes, which its locking enforces
  • event groups, used by the IO manager
  • enough thread-local storage slots — ff_stdio keeps its error state, working directory and error code in three consecutive slots from the index you configure, and its header enforces this at compile time
  • static allocation, if your media driver creates its IO manager mutex statically

Paths must be absolute

Without the working-directory option compiled in, ff_stdio accepts absolute paths only — its relative-path resolver is a pass-through. Give SolidSyslogFileBlockDevice an absolute prefix such as /STORE, so files land at the volume root as /STORE00.log, /STORE01.log. The default short filename mode is sufficient for that naming.

Durability

What the flush does and does not commit is on the platform page, under durability. Read it before choosing your sizes: it decides two settings here.

A graceful shutdown closes the file and leaves data and metadata consistent, so give the application a path that tears the logger down rather than relying on power being cut cleanly. And if the device must survive a hard cut mid-record, size your records and choose the store's discard policy with the loss window in mind.

Memory

The adapter allocates nothing; its instance comes from a static pool. Plus-FAT does allocate — the IO manager's sector cache and its internal buffers come from the RTOS heap — so size that heap for the cache you ask the IO manager for.

When it does not work

Failures report through the error handler rather than silently. Install one before you start, and read error severity for what each level is telling you — a CRITICAL at create time means the file fell back to the Null object, and nothing will be stored.