

RELIANCE EDGE


Reliance Edge is a small, portable, highly reliable power-fail safe file
system for resource-constrained embedded systems like microcontrollers.
It is written in C and provides a familiar POSIX-like file system API,
making it easy to use in your application; or an alternate minimalist
API if your application has simple storage needs. Reliance Edge is
highly configurable and can be tuned to the precise needs of your
application.


Documentation

The complete documentation for Reliance Edge is distributed separately.
It includes an API reference and detailed discussions of various aspects
of using Reliance Edge, including porting, building, configuring, and
testing. This complete documentation, called the _Developer's Guide_,
can be obtained for free from here:

http://www.datalight.com/reliance-edge

In addition this README, see doc/release_notes.md for a list of updates
to Reliance Edge and a list of known issues. There is also a quick-start
guide in the doc/ directory that describes step-by-step how to compile
and run Reliance Edge in a simulated Windows environment.


Why Use Reliance Edge?

Reliance Edge is ideal for small embedded systems with data storage
requirements, especially if there is a chance of sudden power loss or
other system failures. Compared to "raw" disk access, using a file
system like Reliance Edge removes the burden of tracking which sectors
belong to which objects, and allows data to be updated more reliably.
Compared to the FAT file system, using Reliance Edge eliminates the
possibility that file system data will be left in an inconsistent state,
corrupting the disk; Reliance Edge does not need a fsck/CHKDSK utility.
Compared to journaling file systems, Reliance Edge has less overhead and
results in less storage media wear for longer device lifetimes.

Reliance Edge uses a unique transactional model that not only prevents
file system corruption but also allows a set of changes to be made in an
atomic "all or nothing" fashion. This is very useful for applications
that make sets of interrelated changes. By using the features of
Reliance Edge, a set of changes can be incorporated into a single atomic
transaction, which is committed in its entirety or not at all even if
interrupted by power loss; this means the application does not need code
to recover from partially-finished updates.


Hardware

The typical hardware for Reliance Edge is a 32-bit microcontroller, but
other targets are possible. In its typical configurations, Reliance Edge
needs at least 4 KB to 5 KB of RAM, 11 to 18 KB of code space (on the
ROM or NOR flash), and 500 to 700 bytes of stack.

Reliance Edge is not designed for high-end embedded systems that run
complicated operating systems like Linux or Windows Embedded Compact.
Embedded systems of that variety are better served by other file
systems, like Datalight's Reliance Nitro.


Getting Reliance Edge Working

Before you can use Reliance Edge, it must be ported and configured. At a
minimum, porting includes filling-in functions so that Reliance Edge can
issue commands to your storage medium; depending on your needs, other
functions may need to be filled in as well. These functions reside in a
subdirectory in the os/ directory; see os/stub/ for a blank set of
functions. Configuring includes creating a project directory (start by
copying projects/newproj) and creating the two configuration files
(redconf.h/redconf.c) using the Reliance Edge Configuration Utility
(which can be downloaded from http://www.datalight.com/reliance-edge).

These topics are covered in much greater detail in the _Developer's
Guide_, linked above.


Using Reliance Edge

Using Reliance Edge is a simple matter of including the primary Reliance
Edge application header in your application (either include/redposix.h
or include/redfse.h) and compiling and linking against Reliance Edge
binaries. The Reliance Edge driver must be initialized before it is used
(via the red_init() or RedFseInit() functions) and then volumes can be
mounted and file and directory functions invoked. The Reliance Edge API
is documented in the _Developer's Guide_ (linked above) and also via
comments in the source code.


Licensing

Reliance Edge is an open-source project licensed under the GNU General
Public License v2 (GPLv2). Businesses and individuals that for
commercial or other reasons cannot comply with the terms of the GPLv2
license may obtain a commercial license before incorporating Reliance
Edge into proprietary software for distribution in any form. Visit
http://www.datalight.com/reliance-edge for more information. The
commercial distribution also includes extra tests and tools not
distributed with the GPLv2 version.

See LICENSE.txt for the full license terms of this distribution of the
product.


Getting Help

If you need assistance using Reliance Edge, and you have already
consulted the _Developer's Guide_, contact
RelianceEdgeSupport@datalight.com.

In the near future, a community forum or message board will be set up to
facilitate discussion of Reliance Edge and allow users to get help from
Datalight and from each other. In the meantime, please use the email
address given above.


Contributing

Contributions to Reliance Edge are welcome. Our policy is that Datalight
must own the copyright of all code incorporated into Reliance Edge; if
contributing a significant amount of code, you will be asked to file a
copyright assignment agreement. See CONTRIBUTING.txt for further details
and contribution guidelines.

To report bugs, please create a GitHub issue or contact
RelianceEdgeSupport@datalight.com.
