fs: File system functions

The file system functions offers support for standard Windows FAT16/32 format 8.3 file systems. This provides applications with the opportunity to have an almost unlimited storage capacity for extensive data logging, databases, user configurations, etc.

By using standard SD-CARD technology or USB drives, it is straightforward to exchange data with any Windows PC (or any other FAT16/32-compatible platform).

Media	ID	Drive
SD-CARD	0	A:
Internal drive	1	B:
Project drive	2	P:
USB drive	3	U:

The drives are addressed by using the drive name A:, B:, P: or U:, for example "B:\DOC\MYLOG.TXT".

	•fsMediaPresent	Determines if the media is present.
	•fsMediaWriteProtected	Determines if the media is write-protected.
	•fsMediaOpen	Opens a media.
	•fsMediaClose	Closes a media.
	•fsMediaQuickFormat	Formats a media.
	•fsMediaEject	Ejects a media.
	•fsMediaSize	Retrieves the size of the media.
	•fsMediaFree	Retrieves the amount of the free space on the media.
	•fsStatusLEDEnable	Enables or disables status-LED.

	•fsDirCreate	Create a new directory.
	•fsDirChange	Change directory.
	•fsDirCurrent	Retrieves current directory path.
	•fsDirCatalog	Lists all directory items (files and directories).
	•fsDirDelete	Deletes a directory.

	•fsFileCreate	Creates a new file.
	•fsFileOpen	Opens an existing file.
	•fsFileExists	Determines if a file exists.
	•fsFileRename	Renames a file.
	•fsFileMove	Moves a file.
	•fsFileDelete	Deletes a file.
	•fsFileStatus	Retrieves status of an opened file.
	•fsFileGetCreateTime	Retrieves the time of file creation.
	•fsFileGetSize	Retrieves the size of a file.
	•fsFileSeek	Moves the file pointer.
	•fsFilePosition	Gets the current file pointer position.
	•fsFileRead	Reads a block of data from the file.
	•fsFileReadString	Reads a string from the file.
	•fsFileWrite	Writes a block of data to the file.
	•fsFileWriteString	Writes a string to a file.
	•fsFileWriteStringNL	Writes a string that includes a line break at the end to a file.
	•fsFileClose	Closes a file.
	•fsFileFlush	Flushes cached write operations to the media.

The firmware does everything possible to maintain the consistency of the file system. It is ensured that shutting down an operation or performing a controlled reset will automatically be handled by the firmware so that the file system is shut down in a consistent state.

Media removal without the use of fsMediaEject or hardware reset should be avoided as this can result in an inconsistent state of the file system and, in a worst case scenario, even loss of data.

In case of an uncontrolled shutdown, or reinserting a non-ejected media, the firmware will automatically check and repair the file system. As this phase can take some time, the file system will be unavailable until the completion of the operation. The file system API will return a -22 (media is busy) error code during this phase.

In case of a repair operation, the fault entry "Drive X: has been repaired due to unexpected shutdown." will be present in the fault log after the repair has completed, where X is the letter of the media.

The implementation of the FAT format 8.3 file system has the following limitations:

•The file name is restricted to a maximum length of 8 characters plus the 3 file type characters. The "." separator is not included.

•The file name must not contain spaces or special characters. "-" or "_" are both allowed, though.

•A file with a long file name can be accessed with the "~" character, e.g. "Long Filename.txt" is accessed as "LONGFI~1.TXT".

•A directory name must not contain "." or any other special characters as stated above.

•It supports standard SD-CARDs (non-SDHC) with a capacity of up to 2 GB and SD-CARDs (SDHC) with a capacity of up to 32 GB.

•If more than one partition is present on the media, the file system will use the first.

•There is a separate working directory for each thread. When the thread is first started, the working directory is the root of the drive.

The capacity of the internal drive of an NX32L devices ranges from 61 MB to 4 GB and utilizes different types of flash technology.

The total number of writable bytes are limited for any flash technology and is calculated as follows:

TBW is the Total Bytes Written before exceeding the guaranteed endurance of the device.

CAP is the size of the partition where the wear-leveling is performed by the system or media controller. This size will often be different than the size of the internal drive due to compression and other data at the same partition.

WAF (Write Amplification Factor) is between 4 and 8, that depends on the applications write behavior.

For example, large sequential writes produce a lower WAF, while random writes of small data blocks produce a higher WAF. Typically WAF is set to 8.

Device	Capacity (CAP)	Program/Erase (PE)
RTCU NX-200 / NX-400 / NX-900	270 MB	100000
RTCU LX5 pro / LX5 eco	180 MB	80000
RTCU LX4 pro	61 MB	80000
RTCU LX2 pro	4000 MB	3000

Device	Calculation	TBW (MB)
RTCU NX-200 / NX-400 / NX-900	(270*100000) / 8	3375000
RTCU LX5 pro / LX5 eco	(180*80000) / 8	1800000
RTCU LX4 pro	(61*80000) / 8	610000
RTCU LX2 pro	(4000*3000) / 8	1500000

For example, a workload featuring 500 MB of daily write usage cycle will reach end of life as follows:

Device	Calculation	Duration
RTCU NX-200 / NX-400 / NX-900	3375000 / 500	6750 days = ~18 years
RTCU LX5 eco / LX5 pro	1800000 / 500	3600 days = ~9 years
RTCU LX4 pro	610000 / 500	1220 days = ~3 years
RTCU LX2 pro	1500000 / 500	3000 days = ~8 years

The above table shows that care must be taken for write data intensive applications and on the RTCU LX4 pro it is recommended to use an SD-CARD for such applications.

The size of the internal flash drive is specified in the data sheet and/or technical manual of the device in question.

When using the internal flash drive, it must be observed that the flash memory technology used is the same as used for Persistent Memory and Datalogger storage. For this reason, there is a limited number of write operations possible, and the following must therefore be observed:

•The file system will automatically perform wear leveling - thus swapping heavily used sectors in the flash with lesser used sectors.

Using a device with 4 MB or 8 MB internal flash drive the wear leveling, combined with the effective write throughput, basically means that there is no write endurance limitations to be observed.

For devices with a small internal flash drive of 512 KBytes the write endurance limitation must however be observed.
512 KBytes translates into initially 1020 usable sectors, each sector can be rewritten a minimum 100,000 times before wear-out occurs.

The following number of write operations can be expected on the Internal Flash drive:

•With a file OPEN, WRITE and CLOSE operation on the same 512 bytes file, a total number of approx. 51 million write operations can be made.

•With a file CREATE, WRITE and CLOSE operation on a 512 bytes file, a total number of approx. 25.5 million write operations can be made.

•With a file OPEN, WRITE and CLOSE operation on the same 1024 bytes file, a total number of approx. 34 million write operations can be made.

•With a file CREATE, WRITE and CLOSE operation on a 1024 bytes file, a total number of approx. 20.4 million write operations can be made.

Writing every 10 seconds, 24 hours a day, will allow CREATE, WRITE and CLOSE operations on a 1024 bytes file for more than 6 years!

The Intellisync Project Drive is read-only from VPL, and does not support directories. To write to the project drive, it must be synchronized using e.g. the RTCU IDE, using User files. It is not possible to read VSX files from the project drive.