Title: Online SDL flowchart making tool, easy to draw professional SDL flowchart, online SDL diagram design online drawing

What is the SDL

SDL (Specification and Description Language), which defines a Specification and Description Language, is a modeling Language for describing real-time systems. SDL diagrams illustrate the process of modeling the specification and description languages. It can be widely used in automotive, aviation, communication, medical and telecommunications fields.

The SDL diagram has three parts:
  • The system definition
  • block
  • process

The system definition defines the main nodes (blocks) of the system, such as the client and the server, and the block diagram shows more detail. The flow shows the processing steps in each block. Refer to state machines and UML.

The structure of the SDL

  • The overall design of the system is called the system, and everything outside the system is called the environment. There is no specific graphical representation of the system, but a block representation can be used if desired.
  • A proxy is an element in the architecture of a system. There are two kinds of proxies: blocks and processes. The system is the outermost block.

block

A block is a structural element and does not imply any physical implementation on the target. A single block can be further decomposed into multiple blocks to handle large systems. The block symbol is a solid rectangle with its name in the middle

Process

A process is basically the code that will be executed. It is a finite state machine based task with an implicit message queue to receive messages. Multiple instances of the same process can run independently. The number and maximum number of instances that appear at system startup are declared in parentheses following the process name. The full syntax for the procedure notation is: < process name >[(< number of instances at startup >,< maximum number of instances at startup >)] If omitted, the default value for the number of instances at startup is 1, and the maximum number of instances is infinite.



Architecture

The overall structure can be thought of as a tree, and the leaves are the process.

First, a process has an implicit message queue to receive messages listed in the channel.

The process describes a finite state machine based on extensions. The process state determines how the process behaves when it receives a particular stimulus. A transition is the code between two states. The process can hang on its message queue or semaphore, or run such as execute code. Information stimuli from the environment or from another agent to an agent are called signals. Signals received by the process agent are first put into the queue (input port). When the state machine is in a wait state, if the first signal in the input port is enabled for that state, the state machine begins to transition to another state.

Start

The start symbol represents the starting point of the process execution

State

The name of the process state is written in the status symbol

Stop

A process can end with a stop symbol.

Message input

The message input symbol represents the type of message expected in the SDL-RT state. It always follows an SDL-RT status symbol, and if it receives that symbol, the symbol after the input is executed. The syntax in the message input symbol is as follows:

Message output

Message output is used to exchange information. It asynchronously puts data into the receiver’s message queue.

<parameter value> [(<parameter value> {,<parameter value>}*)] TO_XXX... ` ` `! [online] SDL diagram design "online SDL diagram design" (https://www.freedgo.com/public/themes/freedgo/uml/output.png) # # Message save one process may be intermediate state, New requests cannot be processed until the work in progress is complete. These new requests should not be lost, but should be retained until the process reaches a stable state. The concept of saving has been introduced, which basically holds information until it is processed.

The symbol syntax is: <message name> `

Continuous signal

A continuous signal is an expression that is evaluated immediately after a process reaches a new state. It evaluates before any message is entered or saved.

Action

Action symbols contain a set of instructions written in C code. The syntax is the syntax of C.

Decision

A decision symbol can be thought of as a C switch/case.

Semaphore take

When a process attempts to acquire a semaphore, it uses the semaphore to obtain the symbol.

Semaphore give

To give a semaphore, the syntax in “semaphore gives SDL-RT graphic symbols” is :< semaphore name >

Timer start

The syntax in the Startup Timer SDL-RT graphic symbol is :< timer name >(< time value > in the scale count)

Timer stop

To cancel the timer, the syntax in “cancel the timer SDL-RT graphic symbol” is :< timer name >

Task creation

To create a process, the syntax for creating a process symbol is:

<process name>[:<process class>] [PRIO <priority>]

Procedure call

The procedure call notation is used to call an SDL-RT procedure. Syntax SDL graphical notation in procedure calls is standard C syntax:

[<return variable> =] <procedure name>({<parameters>}*);

Connectors

Connectors are used to split a transition into sections so that the diagram remains clear and printable, bringing different branches together at the same point.

Transition option

Branches of the symbol have true or false values. The actual branch is defined when the expression is defined, so the equivalent C code is :#ifdef <expression>

Comment

Comment notation allows you to write any type of informal text and concatenate it to the desired symbol. Comment symbols can be unconcatenated if needed.

Extension

The extension symbol is used to complete the expression in the symbol. An expression in an extension symbol is treated as part of an expression in a concatenation symbol. Therefore, grammar is one of the linking symbols.

Procedure start

This symbol is dedicated to the program diagram. It indicates the process entry point.

Procedure return

This symbol is dedicated to the program diagram. It means the end of the program.

Text symbol

This symbol is used to declare variables of type C.

Additional heading symbol

This symbol is used to declare an SDL-RT specific heading

Example on Behavior

In a state (such as idle), the procedure pulls the first signal from the queue, which is one of the types indicated in the input symbol (in this case, code, containing information from the panel’s card ID and PIN). The idle state is followed by an input symbol that describes the consumption of the signal code. In the transformation after receiving the code signal, it uses the variable CUR_PANEL to remember which panel the signal came from, and then sends the code to the central unit for verification. The next state is validation. In state validation, the controller will accept only normal or abnormal. If it works, it will open the door by calling the program “Open the door.”

SDL vs State Machine Diagram

A chocolate vending machine is an automatic machine that, with the appropriate code inserted, can serve different types of chocolate.

State Machine

A finite state machine consists of a finite number of states, one of which is the initial state, to which multiple transitions connect. In the vending machine (the state diagram example), the circles below represent states and the arrows represent transitions. Each arrow is decorated with an input to trigger the transformation (before the slash) and a list of possible outputs (after the slash).

The Corresponding SDL Diagram

There are many ways to create a network topology. If you choose to draw a network topology online, you are recommended to use the online mapping site Freedgo Design. Freedgo Design, which can be accessed at https://www.freedgo.com. Freedgo Design online mapping website is a multi-type graphic design software, software content comes with rich geometric template, can be used to draw professional network topology, swimlane diagram, influence diagram, SDL diagram, approval diagram, accounting network topology diagram, etc., provide rich examples of network diagram, easier to get started

Now let’s take a look at how to make SDL diagrams using Freedgo Design.

Step 1: Visit https://www.freedgo.com and register a user first. After successful registration, login to the home page

Step # # # 2: visit https://www.freedgo.com/draw-… , enter the drawing page, or from the top of the home page menu click to start making.

Go to the graphics page and clickfile -> New from the type -> The flow chart -> SDL figure

Alternatively, click on the legend, find the flowchart -> SDL diagram in the legend, and select a similar legend to make changes

The software provides a variety of connection styles. In this SDL diagram, you can choose a normal right-angle connection line. On the connection line, you can also enter text for further explanation.

### Step 3:

Topology tool has a rich set of features, users can close the graphics for monochrome fill, gradient fill, text size and position color adjustment. After the pattern filled network topology, the appearance level has been improved a lot.

More examples of basic flow Refer to [illustrations] (https://www.freedgo.com/new/s…