Difference between revisions of "Detailed SDL tutorial"

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(Created page with "= OpenGEODE - SDL Tutorial = == Introduction == SDL is a complex language and the complete specifications are available on the ITU-T website : https://www.itu.int/rec/T-REC...")
 
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== Introduction ==
 
== Introduction ==
  
SDL is a complex language and the complete specifications are available on the ITU-T website : https://www.itu.int/rec/T-REC-Z.100
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SDL is a rich language and the complete specifications are available on the ITU-T website : https://www.itu.int/rec/T-REC-Z.100
  
 
There are several major revisions of the language:
 
There are several major revisions of the language:
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* SDL2010 - the baseline of the current version (latest version is from 2019)
 
* SDL2010 - the baseline of the current version (latest version is from 2019)
  
OpenGEODE does not stick to one version of the standard. It tries to provide the most useful and most known features of SDL and skips the ones that are not compatible with real-time systems.
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In this page we list the features of SDL supported by OpenGEODE and explain how to use them.
  
The basis can be summarized as being SDL92 (including Process, Process Types) + Textual Algorithms (For loops)
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== SDL scope of OpenGEODE ==
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 +
One important features of SDL is the possibility to describe a system made of components that communicate through messages. This description can be nested: a block can contain other blocks that eventually contain actual state machines.
 +
 
 +
This is not directly supported by OpenGEODE because it is done in TASTE using the AADL language.
 +
The semantics are nearly similar, with the following differences:
 +
 
 +
1. SDL does not allow to specify a cyclic message in this view (periodic activation has to be done using timers inside state machines)
 +
However TASTE allows it in the Interface View:
 +
 
 +
:[[File:ClipCapIt-210118-083557.PNG]]
 +
 
 +
 
 +
In this example, the interface named "monitor" is cyclic. A period has to be specified for it.
 +
 
 +
2. In SDL all messages are asynchronous. Direct function calls are possible between two state machines (remote procedure calls) but this communication is hidden from the diagram.
 +
In TASTE, synchronous calls are expressed in the Interface View:
 +
 
 +
:[[File:ClipCapIt-210118-084101.PNG]]
 +
 
 +
Synchronous calls are immediately executed (blocking calls) and can be either protected (mutual exclusion between messages) or unprotected (executed immediately no matter what).
 +
 
 +
3. In SDL all active functions are state machines
 +
In TASTE it is possible to implement them in different languages: SDL, but also Simulink, C, C++, Ada, and even VHDL.
 +
TASTE generates the glue code between the functions.
 +
 
 +
4. In SDL, communication is done via messages (called signals) that are defined at system level. This means that a signal name is unique across the system.
 +
When sending a message, it is possible in SDL to specify the recipient in case several can receive the same signal name. Broadcast and multicast are also supported.
 +
In TASTE, the interfaces are defined at function level. Two functions can therefore have the same interface name but with different semantics (different parameters). It is possible to rename the interface at the sender side,

Revision as of 07:54, 18 January 2021

OpenGEODE - SDL Tutorial

Introduction

SDL is a rich language and the complete specifications are available on the ITU-T website : https://www.itu.int/rec/T-REC-Z.100

There are several major revisions of the language:

  • SDL88 - the first public version
  • SDL92 - major update adding object orientation
  • SDL96 - minor update fixing issues of SDL92
  • SDL2000 - major update introducing new concepts (agents, exceptions, parallel and nested states)
  • SDL2010 - the baseline of the current version (latest version is from 2019)

In this page we list the features of SDL supported by OpenGEODE and explain how to use them.

SDL scope of OpenGEODE

One important features of SDL is the possibility to describe a system made of components that communicate through messages. This description can be nested: a block can contain other blocks that eventually contain actual state machines.

This is not directly supported by OpenGEODE because it is done in TASTE using the AADL language. The semantics are nearly similar, with the following differences:

1. SDL does not allow to specify a cyclic message in this view (periodic activation has to be done using timers inside state machines) However TASTE allows it in the Interface View:

ClipCapIt-210118-083557.PNG


In this example, the interface named "monitor" is cyclic. A period has to be specified for it.

2. In SDL all messages are asynchronous. Direct function calls are possible between two state machines (remote procedure calls) but this communication is hidden from the diagram. In TASTE, synchronous calls are expressed in the Interface View:

ClipCapIt-210118-084101.PNG

Synchronous calls are immediately executed (blocking calls) and can be either protected (mutual exclusion between messages) or unprotected (executed immediately no matter what).

3. In SDL all active functions are state machines In TASTE it is possible to implement them in different languages: SDL, but also Simulink, C, C++, Ada, and even VHDL. TASTE generates the glue code between the functions.

4. In SDL, communication is done via messages (called signals) that are defined at system level. This means that a signal name is unique across the system. When sending a message, it is possible in SDL to specify the recipient in case several can receive the same signal name. Broadcast and multicast are also supported. In TASTE, the interfaces are defined at function level. Two functions can therefore have the same interface name but with different semantics (different parameters). It is possible to rename the interface at the sender side,