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doc/manual/connectors.rst
author Andrey Skvortsov <andrej.skvortzov@gmail.com>
Sun, 06 Jan 2019 01:22:46 +0300
changeset 2499 68f4f2d4516b
parent 1455 4ba27ed51e48
permissions -rw-r--r--
use pregenerated CRC32 lookup tables for retain on Win32 and GNU/Linux

This code could be possible reused on low-end targets with limited RAM.

code to generate lookup table:
[---------------------------------------------------------------------]

/* CRC lookup table and initial state. */
uint32_t crc32_table[256];

/* Generate CRC32 lookup table. */
void GenerateCRC32Table(void)
{
unsigned int i, j;
/* Use CRC-32-IEEE 802.3 polynomial 0x04C11DB7 (bit reflected). */
uint32_t poly = 0xEDB88320;

for (i = 0; i <= 0xFF; i++)
{
uint32_t c = i;
for (j = 0 ; j < 8 ; j++)
c = (c & 1) ? (c >> 1 ) ^ poly : (c >> 1);
crc32_table[i] = c;
}
}

void main(void)
{
GenerateCRC32Table();
int j=0;
for(int i=0; i<256; i++) {
printf("0x%08X, ", crc32_table[i]);
if (++j >= 8) {
j = 0;
printf("\n");
}
}
}
[---------------------------------------------------------------------] 
Beremiz and Beremiz_service connectors 
======================================

To connect a PLC, Beremiz provides 2 types of connectors :
 * a Pyro connector
 * a WAMP connector

To configure the connection, you have to set the *URI_location* in your project Config tab according to this documentation. 

The Pyro connector
----------------------------

Pyro is an advanced and powerful Distributed Object Technology system written entirely in Python.
Beremiz_service spawns a Pyro server, serving a PLCObject (see runtime/PLCObject.py). Therefore, Beremiz acts as a Pyro client.

TODO:: link to PLCObject API documentation

URI_location :
 * LOCAL:// is a facility that starts the PLC service locally and connect Beremiz to it via Pyro.
   This is intended for use in development stage.
 * PYRO://<ip:port> normal connection to a remote PLC. PLC default port is 3000.
 * PYROS://<ip:port> SSL connection to a remote PLC, see below.

more information about Pyro can be found on http://pythonhosted.org//Pyro/1-intro.html

===========================
Setup a Pyro SSL connection
===========================

Pyro v3 has a limited TLS/SSL support based on m2crypto. Pyro v4 had dropped it.
In order to have a full and reliable SSL, we recommand to use a TLS/SSL wrapper as nginx, stub or stunnel.

--------------------
TLS-PSK with stunnel
--------------------

In this example, we setup a simple TLS-PSK connection according to rfc4279.
This ciphersuite avoid the need for public key operations and certificate management.
It is perfect for a performance-constrained environments with limited CPU power as a PLC.


Needed :
 * stunnel >= 5.09

verify openssl support for PSK cipher::

    openssl ciphers -v 'PSK'

----------------------
Client setup (Beremiz)
----------------------

You need to choose an identity for your client, here *client1*.
generate a valid and strong key::

    $ echo client1:$(openssl rand -base64 48) > pskclient1.txt

write a stunnel client configuration file *stunnel-client.conf*::

    output = stunnel-client.log
    client = yes
    
    [beremiz]
    accept = 3002
    connect = [PLC]:3001
    PSKidentity = client1
    PSKsecrets = pskclient1.txt

start stunnel client side::

    stunnel stunnel-client.conf

You could now connect beremiz with classic URI_location = PYRO://127.0.0.1:3002

--------------------
Server setup (PLC)
--------------------

import the client key in a keyfile psk.txt, concatening all client key.

write a stunnel server  configuration file *stunnel-server.conf*::

    output = stunnel-server.log
    
    [beremiz]
    accept = 3001
    connect = 127.0.0.1:3000
    PSKsecrets = psk.txt

start stunnel server side::

    stunnel stunnel-server.conf
    
more documentation on stunnel http://www.stunnel.org/docs.html

The WAMP connector
------------------

WAMP is an open standard WebSocket subprotocol that provides two application messaging 
patterns in one unified protocol: Remote Procedure Calls + Publish & Subscribe.

Beremiz WAMP connector implementation uses Autobahn and crossbar.

URI_location :
	* WAMP://127.0.0.1:8888#Automation#2534667845

more information about WAMP can be found on http://wamp.ws/
beremiz