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: Thursday, February 25, 2021