C51: FLOATING-POINT REENTRANCY IN ISR?

Information in this article applies to:

• C51 All Versions

QUESTION

The documentation states floating-point operations are fully reentrant. Does that apply to interrupt routines as well?

ANSWER

Floating point operations the compiler generates code for (+ - * /) are fully reentrant. But only a few functions in math.h are reentrant.

Those that are not reentrant must be protected from interrupts. One way this can be accomplished is to put a wrapper that disables and re-enables interrupts around the floating point math calls. For example:

#pragma disable        // Disable Interrupts for this function
float ISR_sin (float x)
{
return (sin(x));
}

MORE INFORMATION

• Refer to Math Routines in the Cx51 User's Guide.

SEE ALSO

• C51: SUPPORT FOR FLOATING-POINT NUMBERS
• C51: WHAT ARE THE LIMITS FOR FLOATING-POINT NUMBERS?
• C51: FLOATING POINT LIBRARY ROUTINES REGISTER USAGE
• GENERAL: FLOATING-POINT STANDARD

Last Reviewed: Friday, July 15, 2005