Renesas TM V.3.20A Especificaciones descargar pdf (Pagina 84)

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Renesas Technology, Tools FAQs

Last Updated: March 21, 2000

Document Number: 01051259_e

In the program example, variable b is over written at the line stated by [l=ReceiveByte(4);] in the compiled assembly code. Why

does this happen?

Example program Assembly code

void IntS4R(void)

{

long l;

char c,b;

b=ReceiveByte(4);

l=ReceiveByte(4);

}

void IntS4R(void)

{

long l;

char c,b;

b=ReceiveByte(4);

MOV.B #4,R1L

JSR.A $Receive

MOV.B R0L,-4H[FB]

l=ReceiveByte(4);

MOV.B #4,R1L

JSR.A $Receive

MOV.W R0,-4H[FB]

MOV.W R2,-2H[FB]

EXITD

}

This code is a result of the NC30WA optimization.

In the example program, auto variables b and l exist in different blocks (blocks in which the variable is valid). Variable b is used for

storing a return value of the function ReceiveByte. After that, b is never used. Therefore, variable b can share the same auto area

with variable l.

For this reason, if the variable active blocks do not overlap, NC30WA optimizes the stack area for more efficient processing.

When a write-access to a variable occurs, it appears that the same access happened to variable b. If variable be is in use at the same

time l is in use, the above auto-area overlay will not happen.

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Renesas TM V.3.20A Especificaciones Pagina 84

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