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V4

pC/SFS

In very small devices, there is often not even the possibility to add a normal (parallel) NVM memory to store various data and information.    A very small file system for serial NVM storage devices would be the right solution.    Running FAT-FileSystems on these very small memory is possible, but it can cost a lot of code- and RAM-memory.

   The (small) Serial-File-System presented here is based on simple concatenated blocks whose elements (DIR / FILE) are referenced by a 32bit hash of their name and where the number of max. entries per directory must be defined.    By using a 32bit hash as a name, the file system can be massively simplified, but there are therefore no references to the names of the entries. The hash of each entry must be unique within its directory.    Since a 32bit hash value can not be guaranteed to be unique in itself - that is, if two names have the same hash value - several 32bit hash algorithms are usable, but the selection must be set at compile time.
This file-system handles all names of directories/files as hash over a STRING, so special characters can be used in the names.

reserved names-elements:

.. - one directory back
/  - on the beginning of the Path: for from ROOT
./ - on the beginning of the Path: for from current DIR (optional)
/  - in middle of the Path: as separation for directory/file-names

The whole file-system works case-sensitive !
Various serial NVM memory devices (SPI & I2C) are tested as hardware (MRAM, FRAM, ReRAM, EEPROM). Additional the file system can run too on parallel memory like RAM, FRAM, MRAM or EEPROM. Ideal are all types that support byte-wise writing by internal buffering of sectors/pages, but this can also be done by the low-level hardware driver.
The use of serial flash memory was not provided due to the sector size of ≥ 64kB, the necessary buffering of such an update, as well as the long programming time of an entire page.
When using EEPROM, it is important to remember that 1.000.000 cycles are already quite a lot, but this also indicates a finite lifetime,
In addition, the SerialFileSystem do not respect hot spots (high-update files) or transactions.


memory consumption of the pC/SFS V1.14b:

ROM: approximately 8 kBytes on a 32bit CPU
RAM: approximately 124 bytes global + 42..64 bytes per user + 32 bytes * SFS_HANDLES
         plus approximately 180 bytes stack

tested NVM memory:

MRAM	Everspin MR25H40
FRAM	Ramtron FM25H20, Ramtron FM24V10, Cypress CY15B104Q, Fujitsu MB85RS1MT, Fujitsu MB85RC256, ...
ReRAM	Fujitsu MB85AS4MT
nvRAM	Cypress CY14B101Q2
EEPROM	Microchip 25AA1024, Microchip 25AA1024, Atmel AT25M01, Atmel AT25256, Atmel AT24CM02, STM M95M01, STM M24M02, STM M95512, ONsemi CAT25M01, ONsemi CAT24M01, ...
running on hosts like: ARC-EM, ARMv8-M, FE310, GD32VF103, STM32F1xx, STM32F4xx, SAM3Sxx, SAMD21xx, SAMD51xx, SAML10, SAML11 ... plus Win32 & Linux

But no mechanisms of the File-sharing are deposited. So a file can be opened simultaneously from many users to reading but only from one user to writing.
As file attributes Write-Only and Read-Only are available.

download pC/SFS 1.14b (as ZIP)

Releases:

0.80a	first alpa-Release
0.81a	code for create & delete link can be disabled
0.90a	handling of file attributes completed and code uses found config values from file system if compatible to base settings
0.95b	internal function SFSChange_Entry() harmonised and the use of it readjusted
0.96a	SFS_GetEntry() added, but only the hash of the name can be returned instead the name itself - and optional LOCK/UNLOCK added in LLdriver to protect serial communication against timeouts
1.01b	parallel memory and I2C memory support added, rename of LL-driver files to split between SPI, I2C and parallel memory
1.02a	correction in internal SFSChange_Entry() for incorrect SFS_ChangeDir("/") handling
1.10c	correction in internal SFSMem_Alloc() & SFSCreate_Entry() on creation of a DIR
1.12b	optional extension SFS_RemoveDirTree() added and link handling corrected
1.13a	feature switch SFS_AUTO_CLOSE added
1.14b	feature switch SFS_DEEP_FORMAT added and SFS_PATHNAME central for all strings added, internal functions as static as far as possible

Services of the pC/SFS version 1.14b (abbreviation)
This here presented function overview only serves as short overview.
For detailed information, you please look in Reference-Manual about pC/SFS.

SFS-Control:	Description
SFS_Init	Initialization of the File-System
SFS_GetRev	It returns a pointer on SFS revision
SFS_Flush	saves the SFS as image into a Windows/Linux file
SFS_Format	Format the drive

User:	Description
SFS_BecomeUser	As User announce
SFS_CloseUser	As User cancel

Directories:	Description
SFS_CreateDir	Create a directory
SFS_RemoveDir	Remove a directory
SFS_RemoveDirTree	Remove a directory and all his sub-elements
SFS_RenameDir	Rename a directory
SFS_ChangeDir	Change current path
SFS_ChangeDirTemp	Change current path temorary
SFS_BackDirTemp	returns from temporary path

Files:	Description
SFS_CreateFile	Create a file
SFS_RemoveFile	Remove a file
SFS_RenameFile	Rename a file
SFS_AttribFile	Change the attributes of a file
SFS_GetFileAttrib	It returns the attributes of a file
SFS_GetFileSize	It returns the current size of a file
SFS_GetMaxFileSize	It returns the max size of a file
SFS_OpenFile	Open a file in "mode"
SFS_CloseFile	Close the opened file
SFS_SeekFile	Place the pointer in opened file absolutely
SFS_TellFile	It returns the pointer in opened file
SFS_SetEOF	Set EndOfFile in opened file to actual R/W-pointer
SFS_ReadFile	Read data from opened file
SFS_WriteFile	Write data into opened file
SFS_GetErrNo	read the error-code from Open, Read, Write ...

Links:	Description
SFS_CreateLink	Create a Link to a directory or file
SFS_RemoveLink	Remove a Link

Entries:	Description
SFS_GetEntry	It returns all infos of the given entry (dir/file/link) into a struct

Error-Codes:

Name	Decimal_Value
SFS_NO_ERR	0
SFS_USR_OVF	200
SFS_DBL_USER	201
SFS_NO_USER	202
SFS_NAME_EXIST	210
SFS_NOT_EXIST	211
SFS_PATH_ERR	212
SFS_TMP_DIR	213
SFS_NO_FILE	214
SFS_FILE_RO	215
SFS_FILE_WO	216
SFS_FILE_EOF	217
SFS_NOT_EMPTY	218
SFS_FILE_OPEN	219
SFS_NO_DATA	220
SFS_WRONG_PTR	221
SFS_NO_ENTRY	222
SFS_WRONG_A	223
SFS_LINKED	230
SFS_MAX_LINK	231
SFS_LINK_ERR	232
SFS_NO_LINK	233
SFS_MEM_ERR	240
SFS_MEM_OVF	241
SFS_FORMAT_ERR	250
SFS_PORT_ERR	251