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C51: Reentrancy Issues With the Dallas 390 Math Accelerator

Information in this article applies to:

  • All C51 Versions


Is the Maxim (formerly Dallas Semiconductor) 390 math accelerator reentrant, e.g., can the math accelerator be used in the main C program and in an interrupt?


No. Math operations performed using the math accelerator are not reentrant. The following suggestions will help to guarantee that only one thread of execution uses the arithmetic processor.

  • Use the MODDA directive to compile either
    • Functions which are guaranteed to execute only in the main program,
    • or Functions used by one interrupt service routine.
  • Compile all remaining functions with the NOMODDA directive.



Last Reviewed: Thursday, February 25, 2021

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