LUDIVIN


LUstre DIstribution Visual INterface

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Table of contents

Introduction

Reactive systems are computer systems that react continuously to their environment, at a speed determined by the latter. Synchronous languages have been designed to facilitate the programming of reactive systems. The main synchronous languages are Esterel, Lustre, Argos, and Signal.

One thing that cannot be easily taken into account in synchronous languages is long duration tasks. In Esterel, the only possibility is to use the asynchronous task mechanism (with the exec and return signals). For Lustre, we propose a different approach, which uses the automatic distribution tool ocrep. The principle is to write the Lustre program such that the long duration task is cadenced on a slow clock. The period of this clock must be at least as great as the duration of the task. Then, the distribution specifications needed by ocrep must be written such that all the slow inputs and outputs are assigned to one computing site, while all the remaining inputs and outputs (i.e., the fast ones) are assigned to another computing site. Finally, ocrep must be run with the -r option, in order to desynchronise the slow computing site and the fast one. We call this approach clock driven distribution.

The ludivin tool is a graphical user interface that allows the user to automatise the distribution process with ocrep, be it a manual distribution or a clock driven one.

Description of the ludivin tool

Ludivin is a graphical user interface written in Tcl/Tk. It is an acronym for LUstre DIstribution Visual INterface. As said above, ludivin uses the ocrep automatic distribution tool. Without going into details, ocrep takes as input:

The distribution specifications consist in a partition of the set of inputs and outputs of the program into as many sub-sets as there are computing sites. This assigns a unique computing site to each input/output. Finer specifications can be given by also assigning a computing site to local variables. Concretely, the distribution specification file contains a table of sites, with the same overall syntax as the other OC tables:

site_part        :   /* empty */
                 |   'sites:' number_of_sites site_table 'end:'
                 ;

number_of_sites  :   integer
                 ;

site_table       :   site_table site_definition
                 ;

site_definition  :   site_num ':' identifier '(' signal_list ')'
                 |   site_num ':' identifier '(' signal_list ')' '[' clock ']'
                 ;

site_num         :   integer
                 ;

Here, signal_list is a list of names of input and output signals of the OC program (they are the same as the inputs and outputs of the main Lustre node). The clock indication is optional. Its purpose is to indicate that the related computing location must run at the speed of this clock. The clock true is by convention the base clock of the program, that is, the sequence of its reactions.

FInally, the communications take place through a fully-connected network of FIFO channels. Two communication primitives are used: a sending instruction put and a receiving instruction get which blocks when the queue is empty.

Ludivin is run by invoking the command:

  ludivin

which creates and opens the following window:

The File menu has three commands:

The Ocrep menu has three commands:

Finally, the Help menu has two commands:

The dialog box openned by the Load command is the following:

Once you have selected a Lustre file, ludivin prompts you for the corresponding main node and OC file, by opening the following window:

By default, the name of the OC file is the basename of your Lustre file with the .oc suffix. If you have clicked in the Compilation checkbox, ou if you do not provide the OC file, ludivin will compile your Lustre file. Once this is done, ludivin will parse your Lustre file to compute the tree of all the clocks used in the main node. The root of this tree is always the base clock of the program, which is called true. The clock tree will also be decorated with the inputs and outputs of the main Lustre node, such that each appears next to its respective clock. It will be displayed in the following window:

For instance, here the clock tree contains the root true (with CK and RES attached to it) and a single leaf CK (with IN and OUT attached to it). This window allows you to choose the number of desired computing sites and among two distribution methods:

If you click the open *.rep button, ludivin will ask you to choose an already existing ditribution specification file:

If you do so, you will directly go to the final window. But let us proceed one thing at a time. If you choose the clock driven distribution, type the number of desired computing sites, and click the ok button, you will then have to choose a clock for each site:

To do this, click on the button left to the site, then click on one of the clock from the clock tree above. Do this for all the sites and procced by clicking the >>> button. You will then have to assign each input and output to a unique site:

The clock of a site determines the maximal frequency at which this site will run. Therefore, you can only assign to a site inputs and outputs that are at least as slow as its designated clock. For instance, here you can assign IN and OUT to either the site 0 or 1, but CK and RES can only be assigned to the site 0. Clicking on a clock in the clock tree will automatically select all the remaining inputs/outputs (this is a short cup). Clicking on an input/output will select or unselect it. Clicking on one of the clear buttons will unselect all the inpust/outputs of the corresponding site. Clicking on the reset button will reset all the distribution (after a warning). Finally, clicking on the save *.rep button will allow you to save the current state of the distribution in a chosen .rep file. This distribution does not need to be complete; that is some inputs or outputs can be left unselected at this stage.

Note that the above window reminds you that you have chosen the clock driven distribution method. In the manual distribution case, you will have the following window:

Execpt for the fact that sites have no clock, the method for assigning inputs and outputs to sites is that same as above. In both cases, once you are done, you can clik on the Start distribution button. Ludivin will then check that each input and output is assigned to exactly one computing site, and that in the clock driven case, none of the inputs and outputs assigned to it are faster that its clock. If everything is correct, ludivin will invoke ocrep with the chosen options and will print the result in a window:

The files produced by ocrep will be left in the directory containing the source Lustre file.


Getting ludivin

The ludivin tool is available for Unix architectures:

This distribution of ludivin contains the following directories:

You also need the ocrep executable (available here) and the Lustre to OC translator (available here). Enjoy!

Contributors

Related publications

Last modification: August 28th 2002