MATLAB REAL-TIME WORKSHOP EMBEDDED CODER - S Manuel d'utilisateur télécharger pdf (Page 35)

Some blocks have overflow protection. Blocks like Gain block can saturate the

output if the latter increases or decreases the desired maximum or minimum

values. This is not preferred for code protection since it gives an extra amount of

code lines which takes extra time from the CPU. At the same time it is practical

for critical blocks in the model where the user expect overflow.

Real-Time Workshop Embedded Coder has a convenient way for adding custom

code to the generated code. The user can write custom code to be included in the

header file or the C file of the generated code. The user can write the C-code in

the Custom Code pane of the Configuration Parameters dialog. Another way to

incorporate existing code in the generated code is to use Legacy Code Tool. This

tool transforms an existing C code into C MEX S-function for inclusion in the

Simulink model. If the user does not want to build an S-function from scratch, an

S-function can be built automatically by converting a subsystem into an S-

function. Legacy Code Tool can then be used to include the desired custom code

instead of the S-function used in the Simulink model.

A reference model principle can be used in designing a model in Simulink where

some subsystems are designed as separate models and then added as a model

reference to any kind of design. This results in subsystem saving for reuse in

different projects.

6.3 Fixed-Point Support

Fixed-point is used in microprocessors to represent floating values and a loss of

accuracy often occurs. Scaling is used to convert the real floating value to a fixed-

point value and vice versa.

A value can be, for example, represented as an 8-bit unsigned integer, which

correspond to a range between 0 and 255 (= 12

−

). If the represented value is

between 50 and 150 then almost 60% of the unsigned integer range is unused and

all decimals are ignored when they occur, see Figure 7 below.

Figure 7: Representing a value without scaling

For example the integer representation of 75.7 is, according to the representation

above, 75. A loss of 0.7 can be large depending on the design and the type of the

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MATLAB REAL-TIME WORKSHOP EMBEDDED CODER - S Manuel d'utilisateur Page 35