beremiz

Add retain basic implementation on GNU/Linux

2018-06-07, Andrey Skvortsov
976841968d74
Add retain basic implementation on GNU/Linux

Retain is saved in file and backup of this file is done every time.
File isn't saved on every PLC cycle to avoid high I/O load.
By default, retain is saved every second and on PLC stop/shutdown.
It's possible to override retain flush period by using CFLAGS option
in project's settings. For example, for 0.5 seconds period
use "-DFILE_RETAIN_SAVE_PERIOD_S=0.5".
IEC 61131-3
===========
IEC-61131 is a normative document provided by the standards organization IEC
(International Electrotechnical Commission) and describing a standard for
implementing programmable controllers.
The part 3 of this document (commonly named IEC 61131-3) specifies syntax and
semantics for programming language for programmable controllers. Beremiz
implements all the languages described in this document.
http://www.iec.eu
PLCopen TC6
===========
PLCopen is a vendor- and product-independent worldwide association defining
international standards for various topics related to control programming.
For this purpose, PLCopen has 6 technical committees.
The goal of the sixth committee (TC6) is to define a standard file format,
based on XML, for exchanging programmables controllers programmed using
IEC 61131-3 languages. Beremiz uses this file format for saving the PLC
programs of projects.
http://www.plcopen.org