Configuration of synch - advanced example

Description

In this example, there are three modules: 1, 2 and 3. Module 1 is always active, but modules 2 and 3 are not. Module 1 triggers one scan of modules 2 and 3 when required.

This is set up in the matplc.conf file and in the code of module 1. Modules 2 and 3 are written as normal - MatPLC will suspend them at the beginning of the scan until module 1 triggers them.

In the matplc.conf file:

[PLC]
# We need two places...
# (places hold tokens)
place P_module2 
place P_module3        

# ... and three transitions.
# (when fired, transitions remove and insert tokens from/into places)
transition  T_module2_beg
transition  T_module3_beg
transition  T_launch_modules

# Remove a token from P_module2 when firing the T_module2_beg transition...
arc P_module2     -> T_module2_beg

# Remove a token from P_module3 when firing the T_module3_beg transition...
arc P_module3     -> T_module3_beg

# Insert a token into P_module2,
# and another into P_module3
# when firing the T_launch_modules transition...
arc T_launch_modules -> P_module2
arc T_launch_modules -> P_module3

# The only thing left is to tell each module what transitions to use for
#  the beginning and of the scan.
module2:  scan_beg = T_module2_beg
module3:  scan_beg = T_module3_beg

In the C source code of module1:

In the initialisation:

        /* initialise handle to the synchronisation point... */
        /* Don't forget to add code to check for errors when calling the 
         * following functions:
         *  - If the transition doesn't exist, INVALID_TRANSITION will be returned.
         *  - In case of errors when creating the synchpt, an 
         *     INVALID_SYNCHPT will be returned.
         */ 
        plc_transition_t transition = plc_transition_by_name("T_launch_modules");
        plc_synchpt_t synchpt = plc_synchpt_new(transition, 0, plc_synchpt_blocking);

In the body of the scan (or as appropriate):

        /* If condition occurs, fire the T_launch_modules transition */
        if (???????)
          plc_synch(synchpt);

$Date: 2005/12/08 09:13:44 $